Patent Publication Number: US-7595613-B2

Title: Method and apparatus for electronic power control

Description:
The present application is a continuation of U.S. patent application Ser. No. 11/514,365, filed on Sep. 1, 2006, now U.S. Pat. No. 7,315,151 which is incorporated herein by reference and is a continuation-in-part of U.S. patent application Ser. No. 10/658,589, filed on Sep. 8, 2003, now issued as U.S. Pat. No. 7,102,334, which is incorporated herein by reference and is a divisional of U.S. patent application Ser. No. 10/068,287 filed Feb. 6, 2002, which is incorporated herein by reference and is also a continuation-in-part of U.S. patent application Ser. No. 09/802,809, filed on Mar. 8, 2001, now issued as U.S. Pat. No. 6,366,062, which is incorporated herein by reference and is also a divisional of U.S. patent application Ser. No. 09/241,831, filed on Feb. 1, 1999, now issued as U.S. Pat. No. 6,229,288, which is incorporated herein by reference and is also a continuation of U.S. patent application Ser. No. 08/860,878, filed on Dec. 8, 1997, now abandoned which is incorporated herein by reference and is also a continuation of PCT/US96/00286, filed on Jan. 11, 1996, which is incorporated herein by reference. U.S. patent application Ser. No. 08/860,878 is also a continuation of U.S. patent application Ser. No. 08/371,512, filed on Jan. 11, 1995, now issued as U.S. Pat. No. 5,747,972, which is incorporated herein by reference. 

   TECHNICAL FIELD 
   The invention relates to the field of electrical power conversion and control, across a wide range of current and voltages; more particularly, it relates to methods and apparatus for electronically implemented power control, more particularly, those implemented with switch mode power conversion techniques. 
   BACKGROUND OF THE INVENTION 
   An electrical power conversion circuit is a circuit in which electrical power is changed so that a power source with a voltage or current can serve a load requiring a predetermined voltage or current. In switch mode conversion circuits and power conversion techniques, power is typically changed from a supply that is higher in current or voltage to serve a load requiring lower current or voltage, or from a supply that is lower in voltage or current to a load requiring higher voltage or current. Where high conversion efficiency is made possible by design of the circuit, power output is substantially equal to power input. 
   Where voltage-ampere products (VA) are close to the same at both output and input, and assuming a fixed VA at the input, a reduction in voltage at a resistive load is necessarily accompanied by an increase in load current, and vice-versa. There are three basic classes of switch mode power converters. They include step-down (buck—see  FIG. 1 ), step-up (boost), inverting (including flyback) converters, and “duals” of these three. A “dual” version of any of the three basic class devices can sometimes be effected by a simple transform as follows: series inductors become parallel capacitors and parallel capacitors becomes series inductors. 
   Other transforms can be more involved, and the above transforms are provided as illustrative only, as will be appreciated by those skilled in the art. Dual topologies are known to have the following characteristics: a) discontinuous currents to and from the voltage sources become continuous currents to and from voltage sources; b) the DC transfer function (output voltage vs. input voltage vs. duty cycle) remains the same; and c) the dual input and output inductors can be combined together in one magnetic structure. 
   In such topologies, each converter typically consists of two switches, an inductor, and input and output filters. Nearly all conventional converters are some derivation or combination of these classes and their duals. 
   Output voltage regulation in these known converter topologies then is achieved by varying the duty cycle of the switches.  FIG. 1  shows a simple buck converter with ideal switches. In DC conversion circuits of the type generally known as buck or boost regulators, the two solid state switches typically employed are reciprocally and cyclically operated so that one switch is “on” or conducting, while the other is “off” or non-conducting, and vice-versa. Thus as the duty cycle of the modulation of the two switches is varied, so is the voltage (or current) conversion ratio varied between source and load. For example, in a buck topology, if S 1  is modulated at a given duty cycle D and S 2  is modulated exactly opposite S 1  (S 2  closed when S 1  is open and vice versa) then output voltage is given by the formula:
 
 V   out   =V   in   *D  
 
   Other known formulae similarly apply to other respective known regulator classes, as will be appreciated by those skilled in the art. This relationship holds for either polarity of V in . Theoretically then, alternating voltage on the input would manifest itself on the output according to the same relationship, assuming the use of “ideal” switches. However, as a matter of practice, in the absence of such ideal switches, conventional single stage converter implementations do not function in AC to AC conversions. In conversion circuits used to drive reactive loads such as induction motors, bi-directional energy flows resultant from four quadrant operation must also be accommodated. Simple power transformers are in common usage, though necessarily restricted to AC power conversion; however, they grow heavy and bulky as power levels increase, and they are by nature not readily variable in their conversion ratios without some kind of tap changing modification. 
   There has been some work done in the area of AC converters, but known methods suffer for one or more reasons. For instance, some employ simplistic control schemes that lead to a variety of failure modes in the switches. 
   In all real world switches, there exist timing delays and finite rise/fall times, both of which vary from device to device and over varying operating conditions. If care is not taken in a conventional two switch converter as outlined above, both switches could conduct simultaneously, with attendant high currents and excessive power dissipation which can destroy the switches. 
   Power transistors of some of the types commonly employed as switches in converter topologies (and other semiconductors similarly employed) are known to store significant amounts of charge, and if a control voltage is applied to turn one transistor off as the control voltage is being applied to turn the other transistor on, the flow of current in the first transistor would continue for sometime after the turn off control, and simultaneous conduction in both transistors would occur to cause a short across the power source, with potentially damaging current flow through the switches. 
   A simultaneous “off” condition for both transistors is also a problem, for if the first transistor is turned off before the second transistor is turned on, the series inductor in such regulating circuits (in series with the opening switch) would discharge through the opening switch and subject the switch to potentially damaging voltage. One known technique for dealing with the first phenomenon is the addition of a switching delay, or dead time, into the turn-on of each switch, after turn-off of the other switch. 
   Generally, a value for the length of the switching delay is chosen to insure that one switch is completely off before the other is enabled. In the AC circuit supposed above, however, that then results in both switches being disabled at the same time. Also as discussed above, if any current is flowing in the output inductor L 1 , then the result of both switches simultaneously disabled is a voltage spike across the switches which will likely destroy them. This spike typically has to be clamped via some snubber or clamping network, but that may result in excessive clamp power dissipation and excessive switching losses in the switches. For an example of a manifestation of this problem, and an example of this limiting solution, see U.S. Pat. No. 4,947,311, issued to Peterson. 
   Another approach to the problems described above has been through the use of resonant switching circuits that employ zero voltage or current switching techniques. These are sometimes referred to as “soft switching,” or zero voltage switched, techniques. Converters employing these techniques tend to be more efficient in theory than the “hard” switching circuits using snubbers mentioned above, but some topologies have proven difficult to control, where the resonant circuit becomes increasingly unstable at lower power ranges. In addition, such resonant circuits also have more narrowly defined operating conditions (i.e., minimum and maximum current limitations), and are therefore less robust for industrial applications, and these circuits typically trade switch losses for increased conduction losses, and require bulky resonant componentry. 
   Switching losses into an inductive load, as encountered in conventional circuits, are generally proportional to the product of turnoff time, peak current, peak voltage, and switching frequency, and can be calculated from the well known formula:
 
 P   sw =0.5 t   off   *V   peak   *I   peak *Frequency
 
where P sw  is the switching loss expressed in units of power. In a snubbed or clamped circuit, there is always a voltage rise across the snubber during dead time as long as either current or voltage is non-zero. As a result, there is always a significant switch or snubber dissipation. In addition, during high current surge conditions, the snubber may not be able to adequately limit the voltage rise, leading to potentially catastrophic device failure. These known circuits therefore have significant limits in capability of conversion, at least in terms of output power, efficiency, reliability and cost. This is especially the case with present high power semiconductor technology where higher power and lower cost devices are also generally the slowest, and therefore have inherent and unacceptably high switching losses.
 
   Recently, a variety of other topologies have been suggested for direct AC/AC converters (also sometimes simply referred to as electronic transformers). These suggested topologies have generally fallen into two types: “zero voltage switched” (ZVS) a.k.a. “soft switched” and traditional switchmode topologies, a.k.a. “hard switched”. In those topologies suggested for use in hard switched converters, it appears that the power switches are implemented either as two bidirectional switches or as four unidirectional switches. A control scheme for a two switch converter referred to above is typically some form of simple modulation (such as pulse width modulation or PWM), which schemes make use of dead times, or delays, as discussed above. 
   Where these suggested topologies are implemented with four switches, it appears the corresponding suggested control schemes diverge from one another. Venturini relates to a scheme for switch control as a “staggered commutation.” Alberto Alesina and Marco G. B. Venturini, “Analysis and Design of Optimum-Amplitude Nine-Switch Direct AC-AC Converters,” IEEE Transactions on Power Electronics, vol. 4 No. 1, Jan. 1989. Here, all four switches are required to be controlled at high speed, with both critical timing (including dead times) and level shifting required from a common controller. Cho briefly shows a different scheme which modulates two switches at high speed, but does not define any required dead times or transitions (if any are needed). Jung G. Hoe and Gyu H. Cho, “Soft-Switched Matrix Converter for High Frequency Direct AC-to-AC Power Conversion,” Int. J. Electronics, vol. 72 No. 4, pp. 669-680, 1992. Villaca employs two bidirectional, zero voltage switching (ZVS) switches operating from a simple pulse width modulator. Marco V. M. Villaco and Arnaldo J. Perin, “A New Bidirectional ZVS Switch for Direct AC/AC Converter Applications,” 0-7803-2482-x/95-IEEE Proceedings, pp. 977-983, 1995. 
   These suggested control schemes have a number of points in common: 1) they all have multiple switches operating simultaneously at high frequencies; 2) the timing between these switches is highly critical, in order to avoid cross conduction or voltage spikes from the output inductor; 3) maximum duty cycle may have to be limited to accommodate what may be required as fixed timing delays, and circuit response time to output overload can be consequently dangerously delayed; 4) they all apply high frequencies voltage waveforms to the output inductor, which frequencies are essentially the same from no load to full load and which results in a fixed core loss in the inductor with attendant significant power loss even at light load or no load operation, thus reducing conversion efficiency at light load with attendant increased electricity costs; 5) by employing an unchanging high frequency waveform, the switching frequency AC current component in the output inductor is also similar from no load to full load condition, so that at light load significant current is left circulating through power components like transistors, diodes, and filter capacitors, all with attendant significant power loss and reduced light load conversion efficiency and increased electricity costs; and 6) they all modulate multiple switches at high frequencies, which leads to high average current requirements for control circuitry, especially with large semiconductor power devices like IGBT&#39;s, MOSFET&#39;s, BJT&#39;s and MCT&#39;s. 
   In another vein, three phase power has been the mainstay of electrical power distribution for nearly a century, with three wire (also known as “delta”) distribution being common for most situations. 
   Various methods are currently employed to regulate three phase power, including tap selection, magnetic synthesizers, ferroresonant transformers, inverters and the like. 
   Other known uses for power controllers are so called static VAR compensators, which effectively add or subtract inductance or capacitance from a system, and also adaptive VAR compensators and “dynamic voltage restorers.” These known devices have shortcomings in delivering a variable capacitance or variable inductance to a system, as has been reported in the literature. 
   AC power quality is best and electrical operating efficiency is greatest when the line current is sinusoidal in wave form and in phase with the line voltage. It is well known however that electrical elements such as reactive loads shift the line current in the mains out of phase with the line voltage. This phase shift is commonly defined in terms of “power factor”, or more specifically, “displacement power factor”, where displacement power factor (referred to hereafter for sake of simplicity as PF or as power factor) is given by the well known relationship:
 
PF=cos θ
 
where θ is the degree of phase shift “lead” (or “lag”, as the case might be), also known as the phase angle, between the fundamental voltage and current. A perfect, or in-phase, relationship is equated to 1.0, while increasing degrees of phase shift are represented by power factors decreasing below unity. Power factor is also sometimes defined as the ratio of “true” power (in watts) to apparent power (in volt-amperes, or VA).
 
   Power factor is therefore a measure of relative efficiency of power transfer and energy usage, and becomes more critical with the use of heavy draw machinery and the like, such as motors. Typical induction motor power factors can range from very low at no load to around 0.85 to 0.90 (“perfect” is 1.00) at full load. Electric utility services typically add surcharges to customers with power factors below 0.90. In addition, power factor can be highly variable, depending as it does on the instantaneous total load on the power supply. Power factor correction (“PFC”) then is therefore routinely applied to compensate for bad power factor situations and, through better utilization of the existing power distribution system, to reduce the need for capital intensive additions to the power grid. Power factor correction is conventionally accomplished generally by having a series of capacitors across the line, and incrementally switching the various capacitors in and out with thyristors or relays. 
   Other conventional PFC techniques consist of a bridge of transistors that operate with a storage bank of capacitors or batteries (for example, see Wilkerson U.S. Pat. No. 5,283,726). A major disadvantage of this conventional PFC technique is that the output switches always switch to and from the DC storage bank voltage, which is above the peak power line voltage. As a result, switching losses are quite high. 
   Known automatic power factor correctors are bulky, slow and complex, and therefore only practical for large motors and groups of smaller motors. Even then, it is only the “system average” PF that is corrected, and studies show that it is preferable to correct PF at the load, rather than at the system level. For the above reasons, and other as will be appreciated by those skilled in the art, it is not practical to connect conventional PFC equipment at each load (motor). This is significant in that 60% of the electrical energy produced at this time is consumed by electric motors of 5 HP or greater in size (fully 80% of industrial consumption of electricity is for motors). Any significant reduction in electrical consumption by these motors and/or increase in their efficiency of consumption would result in huge dollar savings. 
   In addition, other elements such as rectifying power supplies and SCR&#39;s, and other non-linear sources such as computers, switchmode power supplies, welders, inverters, controlled bridge rectifiers, fluorescent lights and other lights requiring a ballast, actually alter the sinusoidal waveform of the AC line current. These non-linear devices typically only draw current when the voltage is at its peak, thus causing the harmonic distortion. This is not how the power grid was designed to work. 
   The resulting non sinusoidal current produced by these nonlinear loads can be mathematically resolved into a “fundamental” sine wave current at line frequency, with a number of harmonic waves at multiples of line frequency, with the fundamental producing the power in the load, while the so called “harmonics” only increase heat losses and decrease the system&#39;s power factor (that is, they generally lower the efficiency of the distribution system) with no net contribution to power in the load. The EPRI (Electrical Power Research Institute) estimates predict that by the year 2010, 60% of all electrical loads will be such nonlinear, solid state electronic loads, so that the majority of all future electrical loads will consist of unwanted harmonic generators. 
   This is already even true for conventional PFC techniques that, in addition to other noted disadvantages, also react themselves to exacerbate harmonic problems, amplify circuit resonances, and even cause “ringing” on the mains when capacitors are switched. This ringing can cause malfunctioning and shutdowns in adjustable speed motor drives and other electronic equipment. 
   As discussed above, each non linear device produces its own distorted waveform composed of varying harmonic components. Each device allows current to pass during a portion of the voltage sine wave and blocks the flow of current during another portion of the sine wave. To make matters worse, phase controlled devices such as adjustable speed drives (SCR) generate harmonic currents with amplitudes varying as a function of load change. In addition, the continued trend in government regulation appears to be towards increasing energy efficiency, and is eventually expected to mandate harmonic cleanup at the source. All of this suggests that power quality (PQ) issues are a major concern, and that there is a clear need for PFC and PQ techniques that more efficiently use power without also generating harmonic distortion themselves. 
   It has been suggested that the variety of power quality problems, now extant and steadily growing in magnitude and variety, are all actually summed within a power distribution system, producing effects such as: deterioration of electronic equipment performance, and continuous or sporadic computer and other microprocessor malfunctions; tripping protection circuitry of adjustable speed drives; overheating of neutral in three phase systems, leading to neutral burnout; overheating and premature failure of transformers, even when the transformer rating appears otherwise adequate; overheating of motors; nuisance tripping of circuit breakers; telephone interference; and PFC capacitor fuse blowing. 
   In addition, the need for improved power regulation and/or power conversion is felt in other industries as well. For instance, in the motion picture and entertainment industries, conventional light source dimming technologies produce an audible 60 Hz hum in large studio lamps. The conventional technology generally applied is dimming by means of phase angle fired triacs, which limit the energy to the lamps by basically opening the circuit to the lamps for a given percentage of every half cycle (see example of resultant broken waveform in  FIG. 2 ). This scheme is relatively simple to implement, but is electrically very noisy, which leads to additional design problems and additional implementation costs. A means of smoothly and quietly dimming such lamps would be of great use. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the invention to provide a power controller that is low in electrical and audible noise, applicable to both low and high power applications, having high tolerance for inductive loads, light in weight, digitally controllable, and fast in response time. 
   It is a further object of the invention to provide a power converter having output power, efficiency, reliability and cost superior to known topologies. 
   It is another object of the invention to provide a power converter with reduced total switching losses. 
   It is another object of the invention to provide a power converter that during high current surge conditions and reactive currents is not subject to switch device failure due to voltage rise. 
   It is a further object of the invention to provide a power converter adapted for four quadrant operation and bi-directional power flow, with respect to input and output voltage and current. 
   It is another object of the invention to provide a converter/controller topology that addresses the disadvantages of conventional active PFC techniques. 
   It is another object of the invention to provide a controller topology that can be used as a continuously variable capacitive load. 
   It is another object of the invention to provide a controller topology that can be used as a continuously variable inductive load. 
   It is another object of the invention to provide a controller topology that can be used as a continuously variable resistive load. 
   It is another object of the invention to provide a relatively inexpensive, fast response, self-dampening power factor corrector of size and bulk sufficiently small to be practical for the majority of motors in current and future use, and which does not contribute to line harmonic problems or problems of system resonance and ringing caused by capacitor switching. 
   It is another object of the invention to provide a power controller for assuring best power quality and greatest electrical operating efficiency by controlling an AC source to provide current and/or voltage outputs that are sinusoidal in waveform and in phase with each other. 
   It is another object of the invention to provide a power controller for neutralizing line harmonics. 
   It is another object of the invention to provide a power controller for successfully addressing any one or more of the following power quality concerns: deterioration of electronic equipment performance, and continuous or sporadic computer and other microprocessor malfunctions; overheating and premature failure of transformers, even when the transformer rating appears otherwise adequate; overheating of motors; nuisance tripping of circuit breakers; telephone interference; and PFC capacitor fuse blowing. 
   It is another object of the invention to provide voltage regulation or a power line conditioner to mitigate voltage swells and sags, and overvoltage and under voltage conditions. 
   It is another object of the invention to provide a means of power regulation (voltage and/or current) that has the characteristic of being low impedance source with respect to a load. 
   It is another object of the invention to provide a means of controlling power on single or multiphase distribution systems, including the majority of known power system frequencies, such as 50, 60 and 400 Hz. 
   It is another object of the invention to provide a means of controlling a power converter which allows for nearly instantaneous regulation, among the benefits of which is that the device is non self destructive in overcurrent situations. 
   It is a further object of the invention to provide a means of dimming lamps in such a way as to produce no audible hum. 
   The invention addresses and provides such a system. The invention represents means to quickly, precisely, and remotely convert AC power with losses that are lower than conventionally available technology can provide. It also represents a compact, efficient, and low cost device for processing AC power, and that is simple and reliable and low in harmonic distortion; applicable to both low and high power applications, having high tolerance for reactive and bi-directional loads, light in weight, digitally controllable, and fast in response time. 
   Application of the invention to solutions to power quality problems, especially solutions requiring variable amplification, is especially beneficial in that the invention is the only system that effectively provides full four quadrant operation in a single stage AC to AC power conversion device, particularly with respect to reactive loads, and which utilizes four independently controllable switches. 
   The invention provides an electrical power controller (also sometimes referred to herein as a regulator or converter) apparatus or device for controlling or regulating an AC voltage or current to a load. The voltage may be in single or multiple phase (such as conventional three phase) configurations. The controller device has four independently controllable switches and at least one inductor for each input line (or phase) to be regulated, all in one of several otherwise conventional power regulator topologies, such as buck, boost, inverted or isolated converter/regulators or duals of these topologies. A corresponding regulation or conversion scheme may thus be implemented depending upon the position of the inductor with respect to the switches and the input voltage, as will be appreciated by those skilled in the art. 
   The controller also has a logic control block. The logic control block is comprised in part of a polarity detector in parallel with the input voltage. The polarity detector has two outputs, each of which is the reciprocal of the other (inverted with respect to each other), although this may be accomplished in a number of functionally equivalent ways, such as through use of one or more inverters, as will be appreciated by those skilled in the art. The logic control unit also has a duty cycle modulator with two reciprocal outputs. Each switch is then separately modulated by these detector and modulator outputs under logical control so that some combination of one or more switches is always electrically conducting, or “closed”. In other words, so there is never a combination of all four switches that is open, except of course when the device is not in operation (turned off or out of the circuit). 
   Each switch thus turns off only into the instantaneous line voltage (ILV), rather than switching to a storage bank voltage or DC rail. Since the ILV can be as low as zero, losses are thereby reduced to the extent the ILV is lower than a storage bank voltage or that of a DC rail Typically, this can save 36% or more in switching losses alone, even for resistive loads (with greater savings possible for reactive loads). 
   A variation of this device has 4 OR gates fed by outputs from the polarity detector and the duty cycle modulator through turn off and turn on delays, respectively, such that first and third OR gates each receive as a first input a first output from the polarity detector, and second and fourth OR gates each receive as a first input a second output from the polarity detector; and such that first and second OR gates receive as a 2nd input a first output from the duty cycle modulator, and third and fourth OR gates receive as a 2nd input a second output from the duty cycle modulator. The output from each OR gate controls or modulates or drives one switch or gate each. The switch sources of each pair of switches may be tied together, but do not have to be in some alternate embodiments. 
   In specific embodiments of the controller device, at least one of, and preferably all of, the switches are electronically controllable, though alternate, non-electrical, implementations may occur to those skilled in the art, including partially or fully manual control schemes, and control schemes involving conducted light optics, such as fiber optical control means. Preferably each switch is a solid state switching device, with a diode poled to have a sense opposite to the switch, in parallel across the source and drain of the switch, and the diodes of a pair of such switches are opposite in sense to each other. The switches are preferably transistors, such as BJT (bipolar junction transistors), IGBT, or MOSFET transistors, or even thyristors such as MCT or GTO. 
   One embodiment of the controller device has two switches in series with each other, though poled in the opposite sense from each other, and connected with the inductor to one input, and two switches in series with each other, also poled in the opposite sense from each other, and connected with the inductor to the return. In other words, wherein a first pair of switches is connected between the input and the inductor, and a second pair of switches is connected between the inductor and return. 
   As employed in this disclosure, the term “poled in the opposite sense” when referring to electronic devices that resist or obstruct the flow of current in one direction (usually under a set of defined conditions), but not in the other, means they are placed so that current flow is not blocked in the same direction in both devices; in other words, their “poles” are oppositely arranged, as will be appreciated by those skilled in the art. 
   In another aspect of the invention, there is separately provided a logic controller for controlling the duty cycle of a power controller. The logic controller is particularly adapted for controlling a power controller device that has four independently controlled separate switches. The logic controller has a polarity detector in parallel with the input voltage that has two outputs, and it has a duty cycle modulator that also has two outputs. Each of the outputs of the polarity detector and of the duty cycle modulator are inverted with respect to one another (reciprocal). The controller is employed in such a way that each of the four switches to be controlled is separately modulated so that some combination of one or more switches is always closed. Turn off or turn on delays may optionally be employed. 
   Specific embodiments of the controller device employ four OR gates fed by outputs from the polarity detector and the duty cycle modulator through optional turn off and turn on delays, respectively, such that first and third OR gates each receive as a first input a first output from the polarity detector, and second and fourth OR gates each receive as a first input a second output from the polarity detector; and such that first and second OR gates receive as a second input a first output from the duty cycle modulator, and third and fourth OR gates receive as a second input a second output from the duty cycle modulator. Output from each OR gate modulates or drives one switch or gate each. 
   In another aspect of the invention, a controller chooses its quadrant modes based upon input voltage and error circuit output. A positive input voltage determines that either Quadrant I or Quadrant II will be employed, while a negative input voltage determines that either Quadrant III or Quadrant IV will be employed. The selection of Quadrant I vs. Quadrant II or Quadrant III vs. Quadrant IV is dependent upon the error circuitry. The error circuitry compares output voltage to the reference and determines both the required direction of current flow and the required amount of modulation by way of the error amplitude output to maintain controller output regulation. Current can be in either direction for any particular Quadrant or transition without damaging the controller. 
   This AC electronic power controller is implemented in three parts: 1) a voltage polarity detector senses the polarity of the input voltage and feeds the signal into the Control Logic section; 2) a control input signal is fed into a modulator section (such as a PWM) which converts the input signal into a modulated digital pulse train, which is in turn fed into the Control Logic section (this control input may be fixed, varied and/or sourced by either an external source or error amplifier or corrector of a such types as will be known to those skilled in the art); 3) the Control Logic then takes the polarity and control input signals and implements the control scheme tabularly summarized in Table 2. 
   In specific embodiments, step 2) above is further particularized in that a control input is fed to a programmable reference which in turn produces a variable sine wave reference output (in phase with the input voltage) that is fed into an error correction circuit which compares the reference output to the converter output and provides a resulting signal to the modulator. The logic scheme may be implemented by any of a number of methods as will be appreciated by those skilled in the art, including microcontroller, PAL, or discrete logic. Output from the Control Logic section is then fed into the level shift circuits, which in turn interface the power switches. 
   This specific control scheme has a number of advantages over known and suggested control schemes when applied to the power controller of the invention. 
   1. Since no more than one switch is in operation at high frequency in any given mode, critical timing between or among the various switches in controllers using other schemes is eliminated. 
   2. There is no need for any kind of delay or dead time to be implemented during high frequency switching operation, resulting in greater maximum duty cycle and/or smoother operation from 0% to 100% duty cycle. In addition, overload shutdown response is immediate (or at least substantially reduced), with no delays to step through before shutting down. 
   3. The power controller may be operated discontinuously during no load and light load conditions, resulting in reduced duty cycle for these conditions, with beneficially reduced core loss in the output filter inductor. Light load efficiency is significantly improved, with decreased electricity costs. 
   4. This same discontinuous operation capability also reduces the high frequency current component in the output filter inductor, in turn reducing the amount of recirculating current switched and conducted by the switches and diodes of the converter during light load operation, thus further reducing power loss and further enhancing light load efficiency. 
   5. Since no more than one switch is modulated at any given time, average total switch drive power is greatly reduced. 
   The invention also provides a variable inductor, a variable resistor and a variable capacitor. The variable capacitor of the invention can be made non-resonating, and implementation of these devices appear as linear loads and therefore do not degrade the power factor of the system in which they are employed (i.e., they are “transparent”). The variable capacitor is applicable to an automatic PFC system. These devices are novel with respect to known static VAR compensators, adaptive VAR compensators and dynamic voltage restorers, and implemented as a combination of the power controller of invention and a capacitor connected across an output and a return of the controller whereby the combination functions as a variable capacitor. The power controller of the invention may also be combined with an inductor connected across an output and a return of the controller whereby the combination of controller and inductor functions as a variable inductor. 
   The invention also provides several method aspects. In one embodiment, a low impedance method of power regulation or conversion is provided whereby an amplitude of an input voltage waveform is varied linearly, without respect to its frequency, with or without changing its characteristic waveform, to produce a proportional output voltage to a load, employing only a single stage conversion (i.e., no intermediate DC voltage or current link). 
   In a variation of this method, the above referred to voltage amplitude variation is accomplished by variable duty cycle modulation switching of an input voltage through an inductor in a manner otherwise consistent with conventional power regulation topology. 
   A specific method for accomplishing the variable duty cycle modulation follows these steps: 1) sensing in real time a polarity of the input voltage to derive a pair of polarity signals that are inverted with respect to each other; 2) varying the duty cycle of a modulator, in accordance with and in proportion to the desired modification of the amplitude, the modulator having two outputs inverted with respect to each other; 3) feeding a polarity signal and a modulator output signal to an OR gate, where each signal has a duration, and the beginning of the duration of the duty cycle modulating output signal is delayed, and the end of the duration of the polarity signal is also delayed; 4) using the OR gate logical output to control a switching device for the variable duty cycle modulation of the input voltage. These method steps 1-4 are then iterated separately for each of four OR gates, and the step of variable duty cycle modulation switching of the input voltage includes the step of modulating the switching during operation so that all of the switches in the controller of the invention are not ever electrically non-conducting (or “open”) at the same time (except when there is no power applied to the circuit). 
   Another aspect of the invention is a variable power factor corrector that has a capacitor in parallel with the load to be corrected on an AC line, and a line driven variable voltage output in series with the capacitor for varying the voltage to the capacitor, so as to vary the amount of capacitance reflected through the power controller onto the AC line. In corresponding manner, a line driven variable voltage output is employed in conjunction with other appropriate components to create variable resistors, tuned LC circuits, and variable inductors. 
   Specific embodiments of the power factor corrector have the variable voltage output implemented in an electrical power controller, regulator, or converter, for regulating an AC input voltage. Specific embodiments of such a controller have two pairs of switches, for a total of four switches, and an inductor, and the pairs of switches and the inductor are preferably in one of several conventional power regulator topologies such as buck, boost, or inverted (or some dual). The controller also has a logic controller as described above, so that each switch is separately modulated in such a way that some combination of one or more switches is always closed, or in other words so there is never a combination of all four switches that is open. 
   A specific power factor corrector also has a current sensor in series with a load on the AC line. Both line voltage and current sense signals are fed into a phase delay detector that determines the phase delay between the AC line voltage and the load current. A power factor error amplifier is employed that is fed by an output of the phase delay detector, and the amplifier feeds a signal to the power controller logic controller, to automatically maintain a selected power factor correction on the line. 
   The power factor corrector may also advantageously employ a current sensor in series between the power controller and the load, and a harmonic error amplifier fed by an output of the current sensor, so that the amplifier feeds a signal to the power controller logic controller for auto resonance suppression, harmonic dampening and/or load current shaping. 
   In a variation of the power factor corrector, a plurality of capacitors and a plurality of power controllers are employed for variable and automatic power factor correction in a multiphase AC system. In a three phase variation, a first power controller is in parallel between a first AC line and a third AC line, and a second power controller in parallel between a second AC line and a third AC line. At the same time, a first capacitor is connected between the output of the first power controller and the third AC line, a second capacitor is connected between the output of the second power controller and the third AC line, and a third capacitor is connected between the output of the first power controller and the output of the second power controller. 
   Another variation of the power factor corrector employs a first power controller in parallel between a second AC line and a third AC line, with the power controller fed by a signal derived from a first AC line. A second power controller is in parallel between the first AC line and the second AC line, with the power controller fed by a signal derived from the third AC line. A third power controller is in parallel between the first AC line and the third AC line, with the power controller fed by a signal derived from the second AC line. 
   Another method aspect of the invention provides for power factor correction by reflecting or introducing a continuously variable capacitance onto a power line to correct displacement power factor, where the capacitance is variable by means of a voltage from the power line varied by a power control methodology. 
   This method employs a power control methodology based on variable duty cycle modulation with the following steps: 1) sensing in real time a polarity of the input voltage to derive a pair of polarity signals that are inverted with respect to each other, 2) varying the duty cycle of a modulator, in accordance with and in proportion to the desired modification of the amplitude, the modulator having two outputs inverted with respect to each other; 3) feeding a polarity signal and a modulator output signal to an OR gate, where each signal has a duration, and the beginning of the duration of the duty cycle modulating output signal is delayed, and the end of the duration of the polarity signal is also delayed; 4) using the OR gate logical output for the variable duty cycle modulation of the input voltage. 
   A variation of this method employs, before reflecting or introducing a variable capacitance onto a power line, these additional steps: 1) sensing in real time an amplitude of current on the power line; 2) detecting phase delay (such as by calculating phase delay of current relative to voltage) on the power line in conjunction with the current sense; 3) amplifying an output of the phase delay detection step; then 4) controlling a power factor correction power controller with the amplified output from step 3. 
   Another variation of this method employs, before reflecting or introducing a variable capacitance onto a power line, these additional steps: 1) sensing in real time an amplitude of current on a line between the power controller and the power factor correction capacitor; 2) amplifying an output of the current sense step; 3) controlling a power factor correction power controller with the amplified output. 
   The method of the invention in one aspect involves electronic power control by varying the amplitude of an electrical power supply voltage, independent of frequency, whereby the output frequency will always be the same as the input frequency. An electrical circuit apparatus for accomplishing this function in a specific embodiment is also disclosed herein. The specific circuitry of this aspect of the invention uses four solid state switches, such as IGBT&#39;s, four diodes, an inductor, input and output filters and novel controlling circuitry. The controller apparatus and methods of the invention may be used to implement all otherwise conventional converter types, buck, boost, and inverting (and duals of these) versions to obtain different regulating characteristics, including galvanic isolation of the output from the input. 
   The inventive methods and devices may be used in power factor correction, voltage and/or current harmonic filtering and neutralization, line and load conditioning, improving or changing impedance characteristics of electrical generators, control of power transfer between two power grids, and programmable control of surges, sags, dropouts and most other voltage or power regulation problems. 
   In another aspect of the invention, a method of power factor correction is disclosed employing essentially the same control circuitry in a different application. In essence, a method as disclosed above, employing the control circuitry referred to above, is used to dynamically control the voltage to (and therefore the reflected capacitance of) a single large capacitor (or several if one large enough is not available) that is continuously adjustable with vastly fewer parts than previously thought possible, and all at correction speeds of under 1 second. The circuit can interface between the power line and a PFC capacitor, and/or reactor. As the duty cycle D is varied, the reflected capacitance onto the power line is:
 
 C   refl   =D   2   *C   PFC  
 
   Thus, the capacitor can be continuously controlled between 0 and its given value, and the corrective load presented to the power line can be continuously controlled between 0 and unity times the corrective load in direct connection to the line. If the power factor, or the phase delay, is measured, and fed into an appropriate error amplifier, such as will occur to those skilled in the art, then the control circuitry will automatically correct power factor, even approaching unity, with response time on the order of 0.1 seconds. No other method uses reflected capacitance via a variably controlled voltage source to achieve PFC. 
   The apparatus and method of the invention has no DC storage bank, unlike known converter and PFC correction devices, and only one device is actually conducting output current at any given moment. Furthermore, the turn off voltage varies with the instantaneous line voltage, and (for reactive loads) is at a maximum when output current is at a minimum. Thus, switching losses are dramatically lower than existing methods, and the power factor corrector disclosed has greater output capability and efficiency, and smaller size than known PFC methods. 
   The disclosed PFC method and apparatus can also be configured for three phase PFC for balanced loads by employing two units and three PFC capacitors. In another application, since the invention can vary reactive loads and impedances, it may also be used as a whole or part of a tunable circuit for mitigation of power line harmonic currents, with either manual or automatic tuning of the filter. 
   Yet another extension of the invention includes a relatively fast (several kilohertz or more) loop which is closed around either system (motor and PFC) current or device (invention) output (capacitor) current. The control circuitry can be made to reject and to some degree correct existing harmonic currents that arise from resonances in such systems. Power line harmonic currents are a widely recognized problem in electrical distribution systems. 
   This has great advantage over the common PFC technique where several different capacitors are switched in and out with thyristors or relays. The apparatus of the invention is simpler, smaller, cheaper, and more accurate, and more reliable. It also eliminates the system resonances associated with PFC capacitors. 
   This circuit has the advantage that each switch turns off only into the instantaneous input voltage. The voltage is clamped to that value by an appropriate freewheeling diode, as will be appreciated by those skilled in the art. In a nominal 240 VAC system, average turn off voltage in the circuit of the invention is about 220V, compared to existing systems, such as those employing a DC rail, where a clamp value might be as much as 500V, causing more than double the switching loss over the device of the invention. Thus the invention reduces switching losses to less than half of that common in known circuits, and with no clamp dissipation at all. A circuit with a snubber would require a capacitor so large that the snubber dissipation alone would be several times the total switching loss of the inventive device. The device of the invention reduces total switching losses dramatically over known devices, and this is particularly true while driving reactive loads, where peak line voltage and current are not in phase with each other. This phase separation normally leads to even higher losses in conventional devices. But since, as discussed above, switching loss is proportional to the product of frequency and voltage, this phase difference results in decreased switching losses in devices embodying the invention. 
   Further advantages are that reduced peak voltage results in lower EMI/RFI conducted to input and output; while reduced switching losses allow higher switching frequencies, saving size and weight in input and output filters. Another advantage is that any of several power device types may be successfully employed in the circuit, including bipolar, MOSFET, IGBT, GTO, and MCT devices. Topologies like those disclosed by others (For example, U.S. Pat. No. 4,947,311, issued to Peterson) are not so versatile. Because all four switches in devices embodying the invention are on briefly at zero crossing of the voltage waveform, the current can flow in either direction during that transition without initiating a high voltage spike on the switches during that period. The resulting circuit is quieter, smaller, more efficient, and more reliable than existing treatments. It can handle voltage and current in either direction for true four quadrant operation and true bi-directional energy flow, with the small premium in extra control circuitry more than offset by savings in switch cost, heat sink size and weight, and mechanical size. 
   Another embodiment of the invention comprises a ballast comprising a single common converter circuit that operates in a split mode operation, wherein said single common converter circuit employs a plurality of switch modes to successively modulate one or more of a plurality of switches and diodes; wherein said single common converter circuit can operate as an inverter, a direct converter, or both an inverter and a direct converter; wherein when AC power, DC power, or both types of power are provided to the ballast, a substantially square AC wave and current output is provided from the ballast; and wherein said ballast is used in conjunction with one or more hydrargyrum medium-arc iodide (HMI) lamps. 
   Yet another embodiment of the invention comprises a single stage AC to AC power controller for controlling an AC input voltage to a load, the input voltage having one or more phases, the controller comprising a circuit comprising eight independently controllable switches, one such circuit for each input line to be regulated, the switches of the circuit arranged in a conventional power regulator topology, whereby a selected regulator topology may be implemented, depending upon the position of the switches and to the input voltage; the controller further comprising logic control having a polarity detector in parallel with the input voltage, the polarity detector having two outputs; and a duty cycle modulator having two outputs, wherein one output from the polarity detector is inverted with respect to the output of the polarity detector; wherein one output from the duty cycle modulator is inverted with respect to the output of the duty cycle modulator; and wherein there is always an electrically conducting path through the switches wherein there is at least one switch conducting. 
   In another aspect of the invention, at least one of the switches in the power controller is electronically controllable. In yet another aspect of the invention, the outputs from the polarity detector and from the modulator are electrical. 
   In yet another aspect of the invention, the logic control circuitry comprises eight OR gates; wherein each OR gate is fed by an output from the polarity detector through a turn off delay and by an output from the duty cycle modulator through a turn on delay; wherein the first, third, fifth, and seventh OR gates each receive as a first input an inverted output from the polarity detector; wherein the second, fourth, sixth, and eight OR gates each receive as a first input a non-inverted output from the polarity detector; wherein the first, second, fifth, and sixth OR gates receive as a second input an inverted output from the duty cycle modulator; wherein the third, fourth, seventh, and eighth OR gates receive as a second input a non-inverted output from the duty cycle modulator; and wherein output from each OR gate controls one switch. 
   In yet another aspect of the invention, the electronically controllable switch comprises a solid state switching device. In yet another aspect of the invention, a diode poled to have a sense opposite to the switch is configured in parallel across the source and drain of the switching device. 
   In yet another aspect of the invention, the solid state switching device comprises a transistor selected from the group of devices comprising individual switching devices consisting of BiT, IGBT, MOSFET, MCT and GTO. 
   In yet another aspect of the invention, a first pair of switches is connected between the input and a first inductor, a second pair of switches is connected between the first inductor and return, a third pair of switches is connected between the input and a second inductor, and a fourth pair of switches is connected between the second inductor and return. 
   Another embodiment of the invention comprises a logic controller for controlling the duty cycle of a single stage AC to AC power controller comprising eight independently controlled separate switches; a polarity detector in parallel with the input voltage having two outputs; and a duty cycle modulator having two outputs, wherein one output from the polarity detector is inverted with respect to the output of the polarity detector; wherein one output from the duty cycle modulator is inverted with respect to the output of the duty cycle modulator; and wherein there is always an electrically conducting path through the switches wherein there is at least one switch conducting. In another aspect of the invention eight OR gates are provided, wherein each OR gate is fed by an output from the polarity detector through a turn off delay and by an output from the duty cycle modulator through a turn on delay; wherein the first, third, fifth, and seventh OR gates each receive as a first input an inverted output from the polarity detector; wherein the second, fourth, sixth, and eight OR gates each receive as a first input a non-inverted output from the polarity detector; wherein the first, second, fifth, and sixth OR gates receive as a second input an inverted output from the duty cycle modulator; wherein the third, fourth, seventh, and eighth OR gates receive as a second input a non-inverted output from the duty cycle modulator; and wherein output from each OR gate controls one switch. 
   It is yet another object of the invention to provide a system meeting any one or a combination of all of the needs summarized above. 
   These and such other objects of the invention as will become evident from the disclosure below are met by the invention disclosed herein. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of a known simple buck regulator. 
       FIG. 2  is a graphic representation of a voltage waveform output from a phase angle fired triac. 
       FIG. 3  is a graphic representation of an amplitude modulated sinusoidal voltage waveform output from devices embodying the invention. 
       FIG. 4  is a schematic of one embodiment of the power controller of the invention. 
       FIG. 5  is a block diagram and partial schematic of one embodiment of the power controller of the invention. 
       FIG. 6  is a set a-d of schematic and partial block diagrams of alternate embodiments of the power controller of the invention. 
       FIG. 7  is a set a-d of block diagrams and partial schematics of alternate dual topologies. 
       FIG. 8  is a switch timing diagram for operation of the circuit of  FIG. 4 . 
       FIG. 9  is a block diagram and partial schematic of an alternate embodiment of the power controller of the invention. 
       FIG. 10  is a block diagram of an autovariable power factor corrector. 
       FIG. 11  is a schematic and partial block diagram of a three phase power factor controller of the invention. 
       FIG. 12  is a schematic and partial block diagram of an alternate method of power factor correction with soft start current limits. 
       FIG. 13  is a schematic and partial block diagram of an adjustable capacitor of the invention. 
       FIG. 14  is a schematic and partial block diagram of an adjustable inductor of the invention. 
       FIG. 15  is a schematic and partial block diagram of an adjustable harmonic rejecter of the invention. 
       FIG. 16  is a schematic and partial block diagram of an adjustable resistor of the invention. 
       FIG. 17  is a schematic and partial block diagram of an AC power conditioner of the invention. 
       FIG. 18  is a schematic and partial block diagram of an isolated output AC power conditioner of the invention. 
       FIG. 19  is a schematic and partial block diagram of a high voltage input AC power conditioner of the invention. 
       FIG. 20  is a schematic and partial block diagram of an AC hybrid power conditioner of the invention. 
       FIG. 21  is a schematic and partial block diagram of a hybrid isolated AC power conditioner of the invention. 
       FIG. 22  is a schematic and partial block diagram of an AC voltage regulator of the invention. 
       FIG. 23  is a schematic and partial block diagram of an isolated AC voltage regulator of the invention. 
       FIG. 24  is a schematic and partial block diagram of an adjustable parallel harmonic filter of the invention. 
       FIG. 25  is a schematic and partial block diagram of an adjustable series harmonic rejector of the invention. 
       FIG. 26  is a set a-e of printouts of oscilloscope readings during a test on a prototype PF corrector of the invention. 
       FIG. 27  is a spreadsheet of comparative data on SCR performance vs. an invention prototype power controller. 
       FIG. 28  is a graph of relative efficiencies of conventional power control devices compared to the power controller of the invention. 
       FIG. 29  is a graph of relative harmonics and power factor (for resistive loads) of conventional power control devices compared to the power controller of the invention. 
       FIG. 30  is a block diagram of a specific embodiment of a power controller of the invention. 
       FIG. 31  is a partial schematic and block diagram of a specific three phase delta power conditioner of the invention. 
       FIG. 32  is an alternate block diagram of a specific embodiment of a power controller of the invention. 
       FIG. 33  is a partial schematic and block diagram of a specific embodiment of a high voltage power controller of the invention. 
       FIG. 34  is an alternate partial schematic and block diagram of a specific embodiment of a high voltage power controller of the invention. 
       FIG. 35  is a partial schematic and block diagram of a specific three phase delta high voltage power conditioner of the invention. 
       FIG. 36  is a graphical representation of the square wave mode operation of the HMI ballast over time. 
       FIG. 37  is a schematic of the HMI lamp ballast in operational mode  1 . 
       FIG. 38  is a schematic of the HMI lamp ballast in operational mode  2 . 
       FIG. 39  is a schematic of the HMI lamp ballast in operational mode  3 . 
       FIG. 40  is a schematic of the HMI lamp ballast in operational mode  4 . 
       FIG. 41  is a schematic of the HMI lamp ballast during the zero crossing transition from Positive (mode  1 ) to Negative (mode  5 ). 
       FIG. 42  is a schematic of the HMI lamp ballast in operational mode  5 . 
       FIG. 43  is a schematic of the HMI lamp ballast in operational mode  6 . 
       FIG. 44  is a schematic of the HMI lamp ballast in operational mode  7 . 
       FIG. 45  is a schematic of the HMI lamp ballast in operational mode  8 . 
       FIG. 46  is a schematic of the HMI lamp ballast during the zero crossing transition from Negative (mode  5 ) to Positive (mode  1 ). 
       FIG. 47  is a block diagram and partial schematic of one embodiment of the power controller of the invention. 
       FIG. 48  is a block diagram and partial schematic of an alternate embodiment of the power controller of the invention. 
       FIG. 49  is a block diagram and partial schematic of an alternate embodiment of the power controller of the invention. 
   

   DETAILED DESCRIPTION 
   Referring to the Figures, the invention will be described in specific embodiments by reference to the numerals of the Figures wherein like numbers indicate like parts. 
     FIG. 1  is a conventional configuration of known buck regulator topology, included here as a point of reference. Convention buck regulator  10  may have a first switch  11 , a second switch  12 , input filter capacitor  13 , output filter capacitor  14 , inductor  15 , input  16 , output  17 , and return  18 . Switches  11  and  12  alternately may close and open (may be modulated), so that in conjunction with inductor  15 , in well known fashion, voltage at output  17  may be stepped down from the voltage at input  16  in proportion to the duty cycle modulation of the switches. 
     FIG. 2  is a graphic representation of the broken waveform output from a phase angle fired triac, to be compared with  FIG. 3  which is a graphic representation of an output voltage waveform having its amplitude varied over time by the power controller of the invention, without interruption of the waveform or change to the frequency.  FIG. 2  is typical of phase controlled variable output voltage, in that step down of an instantaneous average voltage at output may be achieved by cutting off a part of the waveform. This process may result in many of the power regulation ills described elsewhere herein. 
     FIG. 4  shows an electrical circuit for use in a specific embodiment of the controller (sometimes also referred to herein as a converter or power converter) apparatus of the invention. The specific circuitry of this aspect of the invention may use four IGBT solid state switches, four diodes, an inductor, input and output filters and novel controlling circuitry. The control circuitry is generally laid out in functional blocks in accordance with  FIG. 5 . The controller apparatus and methods of the invention may be used to implement all otherwise conventional converter types, including buck, boost, inverting, and flyback versions, as illustrated in  FIGS. 6   a - d , and duals of these topologies, as shown in  FIG. 7 . 
   A specific circuit for controlling power to reactive, resistive, or non-linear loads in accordance with  FIG. 5  or  4  may comprise at least four separately controlled unidirectional switches that are all modulated differently according to the polarity of the line voltage according to a logic “box” so that some combination of the four switches is always on, no matter what the polarity is, including the “zero cross” point of polarity change on the input voltage waveform. A specific embodiment of the “box” may comprise a polarity detector, a modulator (preferably a pulse width modulator), and control logic. 
   Those skilled in the art will appreciate that the modulator may use any of several known methods, including fixed and variable frequency, and voltage and current mode, and can be implemented in one or more in a variety of ways, including use of one or more microcontrollers. Any of a number of algorithms can be employed to provide constant, varying, or programmable output (in terms of RMS, average and peak voltage and/or current) to control the modulator. The modulator provides a high frequency (&gt;10 KHz) logic output of between 0% and 100% duty cycle. An additional output of opposite or reciprocal polarity is also provided. 
   During the “zero crossing” of the line voltage (i.e., when input voltage is in transition from one polarity to another), all switches may be turned on simultaneously for a short period of time (it is contemplated that this will be on the order of a few microseconds in specific embodiments) to allow continuous current to flow in the output, as may be necessary. Thus, current can flow in either direction during the zero crossing transition without initiating a high voltage spike on the switches at that time. During this time, the input and output of the circuit may be effectively short circuited by the simultaneous conduction of the four switches. However, the transition may be chosen to occur at a point where the instantaneous input voltage is low enough (near the “zero” crossing—i.e., in the range of +/−4V, or less, depending on the power switches used) that little or no current may be drawn from the input source. 
   Then each time the polarity has cycled, operation may return to that previously described. Thus there are four operational stages per line cycle: Positive polarity, polarity transition (zero cross), negative polarity, and polarity transition (zero cross). As the switches in specific circuits are likely to operate at high and varying voltages, the control logic also includes level shifting as needed to interface with the switches. 
   The power controller  100  of the invention can best be appreciated in detail through a description of its basic schematic building blocks, as illustrated in a specific circuit embodiment in  FIG. 4 . Input block  110  includes jumper JP 1  through which power may be applied to controller  100 . JP 1 - 2  is connected to a power return bus (as is line  2  of output connector JP 2 - 2 ) and this bus is separate from chassis ground (JP 1 - 3  and JP 2 - 3 ). The common power return bus enables controller  100  to be portrayed (at least for purposes of block diagram form, such as for example  FIG. 10 ) as a three terminal component. Input current limiting for catastrophic failure is provided by fuse F 2 . 
   Input filter  120  includes capacitors C 14 -C 18 , inductors L 3  and L 4 , and resistor R 10 . This is a multistage filter which may keep high frequency switching noise out of the input line, reducing conducted EMI/RFI, as will be appreciated by those skilled in the art. R 10  may provide damping for the filter to reduce ringing. R 26  is a bleeder resistor to remove stored charge from the input filter after power disconnection. 
   Power stage  130   a - b  comprises switches Q 1 -Q 4  and diodes D 1 -D 4 . The switches are specifically implemented as IGBT type transistors, though they may also be any of several other types, as detailed elsewhere herein. Each of the four IGBT switches Q 1 -Q 4  is separately controlled, though they form in combination a unique arrangement that, in conjunction with control circuitry disclosed herein, may provide four quadrant operation (see discussion infra) and low switching losses. 
   In specific embodiments, the four switches Q 1 -Q 4  are paired, and each pair Q 1 -Q 2  and Q 3 -Q 4  have their sources tied together, and each of the switches in a pair are poled in the opposite sense to each other. 
   Output overcurrent protection may be accomplished on a cycle by cycle basis via current transformers T 1  and T 2 . Current sense information may be rectified by diodes D 9  and D 10 , fed into sense resistors R 27 -R 29  (block  130   b ), and then compared in the current limit pin U 1 - 9  of modulator IC U 1  (see infra). Switch Q 6  and resistors R 30  and R 31  (block  130   b ) may provide slope compensation to the current sense circuit in order to provide more stable operation under a variety of duty cycles. Diodes D 5 -D 8  may be used to limit transformer T 1 , T 2  leakage reactance voltage spikes on switches Q 1 , Q 2  during turn off. 
   Output filter  140  may provide output averaging and filtering through inductors L 1 , L 2  and capacitors C 12 , C 13 . L 1  and C 12  may average the modulated power stage output into an instantaneous DC value (which varies over time, proportionate to input voltage and to duty cycle). L 2  and C 13  may further filter out the high frequency switching waveform components from the output. Resistor R 11  may bleed off charge from capacitors C 12 , C 13  upon removal of input voltage. 
   Output block  150  includes output connector (upper) JP- 2 , having output high side JP 2 - 1  and power return JP 2 - 2  (which as disclosed above is common with JP 1 - 2 ). Long term output overcurrent protection may be provided by fuse F 1 , while instantaneous limiting may be provided for internally as previously discussed. 
   Polarity detector  160  may detect line polarity via comparator U 8 A and its associated circuitry. Input voltage may be sensed through resistor R 25  and clamped via diode D 15  and switch Q 5  to keep the signal within the common mode input range of comparator U 8 A. U 8 A may detect voltage and provides a small amount of hysteresis (about 1V) to prevent spurious operation in a noisy environment. Some filtering may also be provided via capacitors C 27 , C 28  for the same purpose. 
   Modulator  170  includes IC U 1  which may provide for modulation in this embodiment of controller  100 , using pulse width modulation as its particular method. However, those skilled in the art will appreciate that a number of other conventional controllers and other modulation types may also be employed as desired. 
   Modulator U 1  is an off-the-shelf part used as a modulator/regulator for conventional switching power supplies, and its operation here may be likewise conventional. Timing components R 21 , R 33 , and C 30  may be used to set operating frequency in the 20 KHz to 40 KHz range. Duty cycle may be varied via resistor R 32 , which is connected to the soft start pin U 1 - 8 . There is no regulation loop shown in this particular circuit embodiment, although output voltage and current may be regulated in a variety of ways, including average, instantaneous, RMS, harmonic reduction and/or neutralization, power factor correction, and the like, all as discussed elsewhere herein. Modulator output may be taken from U 1 - 11  (normal) and U 1 - 14  (inverted). 
   Level shifting may be accomplished by means of a variety of conventional methods involving transformers, optocouplers, and the like. In the specific circuit shown in  FIG. 4 , the task may be accomplished with a readily available integrated circuit (IC). This IC provides an optocoupler and high current driver for interfacing with the gate of a MOSFET or IGBT device. Electrical power at the gate may be provided via an isolated transformer winding with rectifier and filter, although a number of equivalent methods may be alternately employed by those skilled in the art. 
   Level shifting block  180  may receive output signals from the logic circuitry (q.v., infra), which may then be shifted in voltage level to drive switches Q 1 -Q 4  via ICs U 2 - 5 , respectively. U 2 -U 5  are stock components that include an optocoupler input and high current MOSFET driver output. They may operate from small power supplies VH and VL which are 15 VDC floating power sources, the conventional derivation of which will readily occur to those skilled in the art. In this case, small linear power supplies may be used but are not shown in the schematic for sake of clarity. 
   Each transistor gate has a series resistor (R 1 -R 4 ) to limit ringing and to control rise and fall times during switching transitions. Each transistor also has a bleeder resistor from gate to source to insure that all devices are in the non-conducting or “off” state in the event that VH or VL are lost. Current into each optocoupler input may be limited by a 1.21K resistor (R 12 -R 15 ) to about 7 mA per the TC4804 specification, with a small capacitor (C 19 -C 22 ) in parallel to speed up the response time. 
   Control logic block  190  includes IC devices U 7 A, U 7 B and U 6 A-D. Operation of control logic block  190  may best be understood from discussion of its three basic modes of operation. In all modes, control logic  190  may take three input signal types (normal modulated output—from U 1 - 11 , inverted modulated output—from U 1 - 14 , and polarity detect—from U 8 A- 1 ) and may translate them into four individual transistor drive outputs, which in turn control Q 1 -Q 4 . It is thus useful to discuss the invention in terms of three modes, corresponding as they do to the three types of input signals received by the control logic unit. This does not negate however the earlier discussion based on four operational stages, corresponding to the four parts of a voltage waveform as it moves in time. For each of the three basic operating modes there are two conditions (discussion of which also sets forth the essence of the full four quadrant operation of the apparatus and method of the invention). 
   First mode is positive polarity of input voltage. During positive input polarity, U 8 A may be low and may hold inverters U 7 B (output) high and U 7 A (output) low. With U 7 B high, both OR gates U 6 B and U 6 D may be high and may turn on Q 2  via U 3  and Q 4  via U 5 . With U 7 A low, U 6 A may be controlled by the modulator output from U 1 - 11 . A turn on delay (rising edge) is provided by R 18  and C 23 . Turn off may not be delayed because diode D 14  may bypass R 18  on the falling edge. U 6 A in turn may control Q 1  via U 2 . 
   At the same time, U 7 A low may allow U 6 C to be controlled by the inverted modulator output U 1 - 14 . It contains a similar turn on delay circuit comprised of R 19 , C 24  and D 13 . Both delay times may be the same and may be sufficient to prevent Q 1  and Q 3  from conducting simultaneously during operation. U 6 C controls Q 3  via U 4 . 
   The two conditions of operation for positive polarity are 1) positive output current, and 2) negative output current. During positive output current, L 1  current may be sourced through Q 1  and D 2  during the Q 1  “on” (conducting) state. When Q 1  is turned off, L 1  current may freewheel through Q 4  and D 3 . Q 3  may be turned on (after delay) during the time that Q 1  is off, but no current may flow through it due to its polarity; the current may pass through D 3  instead. 
   During negative output current, L 1  current may be controlled by Q 3  and may pass through Q 3  and D 4 . When Q 3  is turned off, L 1  current may freewheel through Q 2  and D 1  back to the input. Q 1  may be turned on during that time, but no current may flow through it due to its polarity; current may pass through D 1  instead. 
   The second mode is negative polarity of input voltage. During negative input polarity, U 8 A may be high and may hold inverters U 7 B (output) low and U 7 A (output) high. With U 7 A high, both OR gates U 6 A and U 6 C may be high and may turn on Q 1  via U 2  and Q 3  via U 4 . With U 7 B low, U 6 B may be controlled by the modulator output from U 1 - 11 . A turn on delay (rising edge) may be provided by R 18  and C 23 . Turn off may not be delayed because diode D 14  may bypass R 18  on the falling edge. U 6 B in turn may control Q 2  via U 3 . 
   At the same time, U 7 B low may allow U 6 D to be controlled by the inverted modulator output U 1 - 14 . It may comprise a similar turn on delay circuit  192  comprised of R 19 , C 24  and D 13 . Both delay times may be the same and may be sufficient to prevent Q 2  and Q 4  from conducting simultaneously during operation. U 6 D may control Q 4  via U 5 . 
   The two conditions of operation for negative polarity are 1) negative output current, and 2) positive output current. During negative output current, L 1  current may be controlled through Q 2  and D 1  during the Q 2  “on” state. When Q 2  is turned off, L 1  current may freewheel through Q 3  and D 4 . Q 4  may be turned on (after delay) during the time that Q 2  is off, but no current may flow through it due to its polarity; the current may pass through D 4  instead. 
   During positive output current, L 1  current may be controlled by Q 4 , passing through Q 4  and D 3 . When Q 4  is turned off, L 1  current may freewheel through Q 1  and D 2  back from the input. Q 2  may be turned on during that time, but no current may flow through it due to its polarity; current may pass through D 2  instead. 
   The third mode is polarity transition, with the two conditions being positive transition and negative transition. During positive transition (from negative polarity to positive polarity), Q 2  and Q 4  may be turned on at transition according to the previously described comparator and logic states. Q 1  and Q 3  had been turned on during negative polarity, as explained above, and may not now turn off immediately at this transition because of a delay circuit formed by resistor R 16  and capacitor C 25 . Diode D 11  may prevent any turn on delay during this transition. 
   During negative transition (from positive polarity to negative polarity), Q 1  and Q 3  may be turned on at transition according to the previously described comparator and logic states. Q 2  and Q 4  had been turned on during positive polarity, as explained above, and may not now turn off immediately at this transition because of a delay circuit formed by resistor R 17  and capacitor C 26 . Diode D 12  may prevent any turn on delay during this transition. 
   In some specific embodiments the turn on delay may be comprised of a circuit wherein a high input transition may create a high output transition after some predetermined delay, and a low input transition may result in an immediate (i.e., minimum delay) low output transition. Specifically, this may all be accomplished with a diode, resistor and capacitor combination, such that on a low-to-high transition, the capacitor may be charged high through the resistor, taking an amount of time to reach the logic threshold voltage of the OR gate being driven, thus providing a delay, the amount of which may be selected through selection of the values of the diode, resistor and capacitor referred to above, as will be appreciated by those skilled in the art. Then, on a high-to-low transition, the resistor may be bypassed by the diode and may create a low impedance discharge path to greatly increase the discharge rate of the capacitor. The capacitor voltage may thus be lowered in minimum time, and the logic transition thus may occur with minimum delay. 
   In specific embodiments the turn off delay may be comprised of a circuit wherein a low input transition may create a low output transition after some predetermined delay, and a high input transition may result in an immediate (i.e., minimum delay) high output transition. This also can be accomplished with a diode, resistor and capacitor combination, such that on a high-to-low transition, the capacitor may be discharged low through the resistor and may take an amount of time to reach the logic threshold voltage of the OR gate being driven, and thus may provide a delay, the amount of which also may be selected through selection of the values of the diode, resistor and capacitor referred to above. Then, on a low-to-high transition, the resistor may be bypassed by the diode and may create a low impedance charge path to greatly increase the charge rate of the capacitor. The capacitor voltage may thus be raised in minimum time, and the logic transition thus may occur with minimum delay. For either or both of the turn off and turn on delay methods disclosed, a number of alternate methodologies may be used to create the respective delays, such as use of monostable multivibrators, counters, microcontrollers, and the like, all as will be appreciated by those skilled in the art. 
   As a result of this logic, for either positive or negative transition, the input voltage and output voltage may be momentarily clamped and may likewise be momentarily effectively short circuited to the input/output return and to each other. However, though this runs contrary to conventional thinking, the transition logic events described above all occur at a point in the input voltage waveform where the absolute value of the instantaneous input voltage is actually less than the total semiconductor voltage drops between the input voltage and the input/output voltage return (i.e., less than about four volts in the circuit illustrated). For this reason, no excessive current inputs may be drawn during transition. Output voltage may be held at a minimum voltage, proportionate to the input voltage, as it should be. L 1  current may freewheel appropriately, and no excessive voltage spikes may occur on either the input, the output, or across any of the transistors or diodes in power stage  130 . 
   After turn off delay, transition may be complete, and operation may return to either positive or negative polarity mode, as appropriate, and as discussed above. Overall control logic and operation of controller  100  is therefore fully defined, logically controlled at all times, and smooth in transition for all modes and conditions. 
   In the circuit illustrated in  FIG. 4 , specific component values and/or part types are given in the table below. This list, in conjunction with the schematic and other disclosure herein, will enable the technician or other skilled artisan to construct the circuit disclosed. This list, with such differences as will be appreciated by those skilled in the art also illustrates componentry of other topologies and embodiments disclosed herein. 
   
     
       
         
             
             
             
           
             
                 
                 
             
             
                 
               Drawing Numerals 
               Part Type 
             
             
                 
                 
             
           
          
             
                 
               C1-C8 
               .1UF 
             
             
                 
               R30 
               1.00K 
             
             
                 
               R12-R15 
               1.21K 
             
             
                 
               D11-D15 
               1N4448 
             
             
                 
               Q5 
               2N3906 
             
             
                 
               Q6 
               2N7000 
             
             
                 
               C13-C15 
               2UF 400V 
             
             
                 
               R5-R9 
               4.99K 
             
             
                 
               R10 
               5.1 10W 
             
             
                 
               C12, C16-C18 
               5UF 400V 
             
             
                 
               R31 
               6.21K 
             
             
                 
               R1-R4, R27-R29 
               10.0 
             
             
                 
               R16-R21 
               10.0K 
             
             
                 
               R32 
               10K 
             
             
                 
               R33 
               20K 
             
             
                 
               F1, F2 
               25A 
             
             
                 
               L4 
               30UH 
             
             
                 
               C27 
               47PF 
             
             
                 
               L2, L3 
               50UH 
             
             
                 
               R11, R25, R26 
               82K 2W 
             
             
                 
               R22 
               90.9K 
             
             
                 
               R24 
               100K 
             
             
                 
               C19-C26 
               100PF 
             
             
                 
               C9-C11 
               100UF 
             
             
                 
               C28, C29 
               220PF 
             
             
                 
               L1 
               240UH 
             
             
                 
               R23 
               453K 
             
             
                 
               C30 
               4700PF 
             
             
                 
               U7 
               CD4049UB 
             
             
                 
               U6 
               CD4071B 
             
             
                 
               D9, D10 
               HER105 
             
             
                 
               D5-D8 
               HER305 
             
             
                 
               D1-D4 
               HFA25BP60 
             
             
                 
               JP1 
               INPUT 
             
             
                 
               Q1-Q4 
               IRGPC50U 
             
             
                 
               U8 
               LM393A 
             
             
                 
               JP2 
               OUTPUT 
             
             
                 
               T1, T2 
               PE51687 
             
             
                 
               U2-U5 
               TC4804 
             
             
                 
               U1 
               UC3824 
             
             
                 
                 
             
          
         
       
     
   
   The functional blocks discussed above with reference to  FIG. 4  can be further understood now by reference to  FIG. 5 . Power controller  100  (also sometimes referred to herein as a converter) may comprise four OR gates  181 - 184  in logic control unit  190  fed by outputs from polarity detector  160  and duty cycle modulator  170  through turn off delays  194 ,  195  and turn on delays  192 ,  193  such that OR gates  181 ,  183  each may receive as a first input an output from the polarity detector  160  (inverted) through delay  194 , and OR gates  182 ,  184  each may receive as a first input an output from the polarity detector  160  through delay  195 . OR gates  181 ,  182  each may receive as a second input an output from the duty cycle modulator  170  through delay  192 , and OR gates  183 ,  184  each may receive as a second input an output from the duty cycle modulator  170  through delay  193 . The output from each OR gate, through appropriate level shifting in level shift block  180 , may control or drive one of four switches Q 1 -Q 4  in power stage  130  (through its respective gate) each. 
   In a specific embodiment, the switch sources of each pair of switches may be tied together, as illustrated in  FIG. 5 , but do not have to be in some alternate embodiments, such as that shown in  FIG. 9 . Specifically, each switch may be a solid state switching device, with a diode, poled to have a sense opposite to the switch, in parallel across the source and drain of the switch, and with the diodes of a pair of such switches opposite in sense to each other, as illustrated. Specifically, the switches may be transistors, such as the IGBT transistors illustrated for Q 1 -Q 4 . 
   This embodiment of controller  100  has a buck regulator type of topology, but has two switches in series with each other, poled in the opposite sense from each other, and connected with inductor L 1  to input  110 , and two switches in series with each other, also poled in the opposite sense from each other, and connected with inductor L 1  to return  101 . 
   The buck regulator general form of controller  100  in  FIG. 5 , can better be seen in  FIG. 6   a , along with other conventional regulator type configurations for controller  100 .  FIG. 6   b  shows controller  100  in step-up or boost configuration.  FIG. 6   c  shows controller  100  in inverting regulator configuration.  FIG. 6   d  shows controller  100  in isolated or flyback configuration. 
   As a further illustration of the versatility of the invention, and its potential for replacing conventional topologies without their disadvantages,  FIG. 7  shows the corresponding “dual” transforms for each of the four topologies shown in  FIG. 6 .  FIG. 7   a  shows controller  100  in step-down or buck dual configuration.  FIG. 7   b  shows controller  100  in step-up or boost dual configuration.  FIG. 7   c  shows controller  100  in inverting regulator dual configuration.  FIG. 7   d  shows controller  100  in isolated inverting dual configuration. 
   The resulting output voltage from controller  100 , under any input voltage mode or output current condition, may be equal to the product of the input voltage and the modulator duty cycle, as more fully discussed elsewhere herein. Slight deviations may exist, due to turn on delay times and semiconductor and resistive voltage drops, as will be appreciated by those skilled in the art, but the overall waveform purity is excellent in the disclosed circuit, especially at higher voltages (such as 230 VAC and up). 
   The controller or converter apparatus and method of the invention is envisioned for use in a wide range of applications via a range of alternate topologies disclosed herein. For instance, it is envisioned that control modules comprising the apparatus or methodology of the invention can be made for manual usage, power factor correction and automatic power factor correction, as a universal line conditioner, a motor economizer, and as a harmonic neutralizer. Other uses such as industrial process controls can be accessed via standard industrial interfaces such as the 4-20 mA current loop, and any one of a number of other standard control interfaces, such as RS232, RS485, IEEE488.2, VXI, 0-10V, 0-5V, +/−10V, +/−5V, and manual. Power converters envisioned can be made for use in a wide range of operating voltages and currents, from for instance 120 VAC, 1.5 KVA to 600 VAC, 200 KVA; and even beyond this range, higher amperages can be accommodated by paralleling two or more of the converter modules of the invention, and higher voltages and currents may be controlled via a controller/transformer hybrid. 
   In a specific method of the invention, with all four transistor switches separately controlled, and modulated differently according to the polarity of the input voltage, a sequence can be implemented whereby each switch turns off only into the instantaneous line input voltage, as graphically represented in the timing diagram of  FIG. 8 . In  FIG. 8 , an idealized line voltage is shown schematically as a sine wave with representative cross over points  901 ,  902 ,  903  (the points where the waveform line crosses the “zero crossing” line, emphasized by vertical dashed lines, and corresponding to the point in time where the waveform shifts from one polarity to the other). A pulse width modulation (PWM) signal  920 , capable of ranging between 0% and 100% (and here illustrated at about 50%), and its “anti-modulated” reciprocal  921 , may be fed into a logic network, such as has been described herein, along with the output from a line polarity detector. 
   When line voltage (polarity) is positive (time duration  910 ), switch Q 1  may be pulse width modulated (on and off), each “on” time  911  slightly delayed relative to the corresponding rising edge  912  of the PWM, and in like manner, Q 3  may be anti-modulated (i.e. the opposite state of Q 1 , or in other words, when Q 1  is on, Q 3  is off, and vice-versa). A small delay or dead time  913  may be added for each turn-on of each switch (emphasized with dotted lines) to avoid simultaneous conduction, where the amount of time may depend on the characteristics of the particular switch employed, all as will be appreciated by those skilled in the art. Q 2  and Q 4  may remain on  915 ,  916  at all times during this positive polarity operational phase. 
   When line voltage polarity is negative (time duration  930 ), Q 2  may be pulse width modulated and Q 4  may be anti-modulated (i.e. the opposite state of Q 2 ). Again, a small delay  913  (present, but not emphasized with dotted lines) or dead time may be added for the turn-on of each switch to avoid simultaneous conduction, and Q 1  and Q 3  may remain on  935 ,  936  at all times during this negative polarity operational phase. 
   At crossover  902 ,  903 , Q 3  turn off delay  941  and Q 4  turn off delay  942  (emphasized with dotted lines) may assure that at least one switch (preferably all switches, as here illustrated) may remain on, or conducting. All switches may be turned on simultaneously at this zero cross for a short period of time (on the order of a few microseconds) to allow continuous current to flow in either direction during zero crossing transition without initiating voltage spikes on any of the switches at that time, as more fully disclosed elsewhere herein. This may be all be summarized in Table 1. 
   
     
       
         
             
             
           
             
               TABLE 1 
             
           
          
             
                 
             
             
               INPUT 
               SWITCH STATES 
             
          
         
         
             
             
             
             
             
          
             
               POLARITY 
               Q1 
               Q2 
               Q3 
               Q4 
             
             
                 
             
             
               POSITIVE 
               MODU- 
               ON 
               
                 MODULATE 
               
               ON 
             
             
                 
               LATE 
             
             
               NEGATIVE 
               ON 
               MODULATE 
               ON 
               
                 MODULATE 
               
             
             
               TRANSITION 
               ON 
               ON 
               ON 
               ON 
             
             
                 
             
             
               Note: 
             
             
               “MODULATE” is the opposite of “ MODULATE ” 
             
          
         
       
     
   
   In  FIG. 30 , an alternate control logic for logic section  190 , with additional control input  210  to modulator  170 , may be implemented as summarized in Table 2. 
                                           TABLE 2               Mode   Voltage   Current   Q1   Q2   Q3   Q4                  Quadrant I   +   +   mod   on   off   On       Quadrant II   +   −   off   on   mod   Off       Quadrant III   −   −   on   mod   on   Off       Quadrant IV   −   +   on   off   on   mod       Voltage Transition   0   x   on   on   on   On       (+ to −, − to +)       Mode Transition   +   x   off   on   off   On       (Quadrants I to II,       II to I)       Mode Transition   −   x   on   off   on   Off       (Quadrants III to IV,       IV to I)       Shutdown   +   x   off   on   off   On       Shutdown   −   x   on   off   on   Off                    
where “mod” means modulate (i.e., by means of PWM, pulse frequency modulation, or the like as will be known to those skilled in the art); where “x” means that it does not matter what the polarity of the current is; where “Mode” refers to the various operating states that can occur during operation of the power controller; where “Voltage” refers to the input voltage polarity of controller  100  (from the polarity detector  160 ) and where “0” refers to the voltage transition point; where “Current” refers to the output current polarity from power controller  100 ; and where Q 1 , Q 2 , Q 3 , and Q 4  are the outputs that define the operation of those respective power switches. These switches may interface with the control logic section  190  via conventional level shift circuitry  180 .
 
   It should be kept in mind that, while a mode transition might look inconsistent with an “x” as a current state, in the various Quadrant modes, current is a desired output resulting from the logic scheme rather than an input to it. In specific embodiments, converter  100  chooses its quadrant modes based upon input voltage and error circuit output (in modulator  170 ). Thus, a positive input voltage may determine that either Quadrant I or Quadrant II may be employed, while a negative input voltage may determine that either Quadrant III or Quadrant IV may be employed. The selection of Quadrant I vs. Quadrant II or Quadrant III vs. Quadrant IV may be dependent upon the error circuitry on the other hand. The error circuitry may compare output voltage to the reference and may determine both the required direction of current flow and the required amount of modulation by way of the error amplitude output to maintain converter output regulation. 
   Thus, in the practice of the invention in this aspect, current can be in either direction for any particular Quadrant or transition without damaging the converter  100 . In operation, the logic scheme summarized above for controlling the power switches may drive the output current in the right current direction; the transitions serve only to provide a controlled and nondestructive logic transition between operating modes. It should also be noted that both Mode and Voltage transitions are short term events that last in the range of a few hundred nanoseconds to several microseconds, with typical times on the order of a microsecond. 
   Quadrant selection in these embodiments can be roughly analogized to changing motor directions in a motor driven watercraft. The motor has both direction (forward and reverse) and magnitude (throttle) control, which correspond to quadrant modes and modulation amplitude, respectively. It is clear then that it may not be necessary for either the boat, or the converter, to be stopped (zero output current) in order for the boat to change motor directions, or for the converter to transition between modes. 
   The advantages of the control logic scheme summarized in Table 2 are several: 1) It may provide for a truly instantaneous regulator because only one switch is modulated at a time, whereas other schemes use a sequence or a series of switches and the whole sequence or series may have to run before a return to a changed switch state; 2) There are no deadtimes. This differs from some disclosed embodiments where deadtimes may be applied to prevent simultaneous conduction across power switches. In this scheme there may be no opportunity for cross conduction; the switching may be virtually instantaneous; 3) Lower switching losses and discontinuous conduction at lower power ranges may allow for higher efficiency; 4) No snubbers may be required, so there may be no snubber losses; 5) It can make use of an “all on” zero crossing; 6) It may provide for devices with true four quadrant operation and bidirectional power flow. 
   In  FIG. 32  a specific embodiment of the power controller  100  is shown in block diagram form, with particular reference to variation of details of input to the modulator section  170 . Sine wave reference  162  may feed polarity switch  163 , may be in phase with the voltage at input  110 , and may be derived from any of a number of known sources. For instance, a sine wave generator, phase locked to the input line, or a microprocessor look up table, could be used. The input voltage itself, attenuated and optionally filtered to eliminate harmonics, could also be employed in some applications. 
   Voltage polarity detector  161  may sense the polarity (+ or −) of the input voltage at the input of power stage  130 . When input voltage is positive, detector  161  may output a high logic state to all polarity switches  163 - 165  and to control logic  190 . When input voltage is negative, detector  161  may output a low logic state. 
   If polarity switches  163 - 166  receive high logic input, they may pass their input directly to their output; if they receive low logic input, they may first invert their input signal, then may pass it to output. This configuration is preferred over a simple full wave rectification block. In order for the error corrector  172  to properly signal modulators  173  and  174 , all references and error signal inputs must be referenced to the polarity of the voltage across the input to power stage  130 . Output voltage and current transients and rings could temporarily change polarity, but the error signals must not change polarity state or else error corrector  172  will amplify errors rather than correct them. 
   Gain control  171  may receive input from polarity switch  163  and sine wave reference  162 . It is an adjustable attenuator varying the amplitude of the reference signal to error corrector  172 . Gain control  171  also may receive input from control input  210  which is an external input to determine overall output level, as will be appreciated by those skilled in the art. In a specific embodiment, it may be a digitally controlled attenuator, but in some applications, a simple potentiometer would suffice. Error corrector  172  then may compare the attenuated reference signal with the output voltage from output  150  and, optionally, the output current, from optional current sense  220 , one or both of which may be run through optional attenuator  230  and then through polarity switches  164  and  165 , respectively, as described above. Error corrector  172  then may output a signal to modulators  173  and  174  that may keep power controller  100  output  150  accurately following the reference. In a specific embodiment, this may be accomplished with a single error amplifier, although a microcontroller may also be used advantageously, as will be appreciated by those skilled in the art. 
   Each of the modulators  173  and  174  may receive an input from error corrector  172  and may convert it to a digitally modulated output. This may generally be in the form of PWM ranging from 0% to 100% at frequencies preferably between 10 KHz and 50 KHz, depending upon the application. Other frequencies and other modulation methods such as pulse frequency modulation (PFM) may be employed as well. In a specific embodiment, each modulator may comprise a triangle waveform generator and a comparator. The triangle waveform itself may be fed into the negative input of the comparator and the error corrector output may be fed in the positive input of the comparator. The comparator output of each modulator may then be fed to control logic  190 . Each modulator may have its triangle wave input offset from the other in order to allow a sequential response from the modulators according to the output of error corrector  172 . For instance, in a specific embodiment, triangle waves of 2.5V peak to peak may be offset in relative steps of 2.5V as they feed into the modulator comparators. Modulator  173  (for Q 1 , Q 2 ) then may respond to error corrector outputs of 3.5 VDC to 6.0 VDC, while modulator  174  (for Q 3 , Q 4 ) may respond to error corrector outputs of 1.0 VDC to 3.5 VDC. In addition, the output of modulator  174  may be inverted. The overall output response of the modulators may therefore be in accordance with Table 3 (where “1” is “on”, and “0” is “off”). 
   
     
       
         
             
             
             
           
             
               TABLE 3 
             
             
                 
             
             
               Error Corrector 
               Q3, Q4 Modulator 
               Q1, Q2 Modulator 
             
             
               Output 
               Output 
               Output 
             
             
                 
             
           
          
             
               0.0 V to 1.0 V 
               1 
               0 
             
             
               1.0 V to 3.5 V 
               MODULATE 
               0 
             
             
               3.5 V to 6.0 V 
               0 
               MODULATE 
             
             
               &gt;6.0 V 
               0 
               1 
             
             
                 
             
          
         
       
     
   
   Outputs from polarity detector  161  and the modulators may be fed into control logic  190 , which may output power transistor drive signals according to Table 2 or 4. Optional current sense  220  may sense for overcurrent protection or for output current regulation into a load. It is preferably a current transformer, but may also be via an isolation amplifier, hall effect sensor or other means known to those skilled in the art. Attenuator  230  is preferably a simple resistive divider. 
   Where the power converter of the invention drives only nonreactive loads (i.e., in Quadrants I and III only), a simplified logic scheme may optimally be employed, as summarized in Table 4. 
   
     
       
         
             
             
             
             
             
             
             
           
             
               TABLE 4 
             
             
                 
             
             
               Mode 
               Voltage 
               Current 
               Q1 
               Q2 
               Q3 
               Q4 
             
             
                 
             
           
          
             
               Quadrant I 
               + 
               + 
               mod 
               on 
               off 
               on 
             
             
               Quadrant III 
               − 
               − 
               on 
               mod 
               on 
               off 
             
             
               Voltage Transition 
               0 
               x 
               on 
               on 
               on 
               on 
             
             
               (+ to −, − to +) 
             
             
                 
             
          
         
       
     
   
     FIG. 33  illustrates a high voltage regulator  1000  embodiment of the invention comprised of two power converters  1001  and  1002  of the invention and a transformer  1050 . An input voltage from an AC source is connected to VIN (high)  1090  and VIN (low)  1020 . VIN (high)  1090  and VIN (low)  1020  connect to primary winding  1051  of transformer  1050 , and VIN (high)  1090  also connects to output  1061  of controller  1001 . Output  1062  of controller  1002  is connected to VOUT (high)  1030 , while VIN (low)  1020  is connected directly to VOUT (low)  1040 . 
   Both controllers have as their voltage source secondary winding  1052  and each controller may be controlled independently so that the difference in output voltages of the two controllers may be algebraically added to input voltage at VIN (high)  1090 . For example, if the input voltage is 10,000 VAC and the secondary winding is 500 VAC, which is within the operating range of the invention controller, both controllers may be controlled to remain at zero output voltage when no regulation is needed, since the difference between the two controller outputs is thus zero, and the input voltage passes to the output at VOUT (high)  1030  unmodified. It will be appreciated that the difference is also zero if both controllers are modulated to some identical, but non-zero, voltage, except that that would not be as efficient a usage of power in the controllers themselves. If controller  1002  is modulated to increase its output voltage with respect to its return, and if controller  1001  is controlled to produce zero output voltage, then an AC voltage equal to the difference in output voltages of the two controllers is added to VIN (high)  1090  and sent to VOUT (high)  1030 . This output addition may typically be adjustable from OVAC to 500 VAC. 
   Then to achieve a like continuously adjustable subtraction of voltage from VIN (high)  1090 , controllers  1001  and  1002  may be modulated inversely from that outlined above, so that  1001  has increased output while  1002  remains at zero. In this manner, for the given example, voltage may be continuously varied from about 9500 VAC to 10,500 VAC (10 KVAC-500 VAC to 10 KVAC+500 VAC), for a total high voltage regulation range of +/−5%. 
   In  FIG. 34  an extended range high voltage AC regulator  1080  is illustrated. Extended range (for instance over that associated with the embodiment in  FIG. 33 ) may be achieved by adding another secondary winding  1053  and another pair of power controllers  1003  and  1004 . The two pairs of controllers illustrated are connected as shown in series with each other (output  1062  connected to output  1063 ), and the outputs of each pair may thus be simply added to each other and to VIN (high)  1090 . The number of controller pairs employed in this fashion may also be increased to achieve any particular desired regulation range (in the example above, thus adding 500 VAC of range per pair). Optional conventional fail sense circuitry may be employed in such multiple pair embodiments to insure that operable pairs continue to provide maximum range leaving off only the failed pair(s). 
     FIG. 35  illustrates a three phase delta high voltage conditioner  1110  embodiment corresponding to the single phase embodiment of  FIG. 34 . Three transformers  961 ,  962 ,  963  have their respective primaries connected to the respective phase input voltages  971 ,  972 ,  973 . These are shown as three separate transformers, although a single conventional three phase transformer may also be employed. Each transformer primary has two associated secondary windings for the purpose of adding or subtracting voltage from the input voltage as previous described for  FIGS. 33 and 34 . As it may typically be desirable to keep the output of such a system in phase with the input, especially when employing the circuit in utility applications, each phase may be modified by two power controller pairs. For example, to regulate phase A, it may be fed through controllers  1001  and  1002  (delta phase C-A) and controllers  1007  and  1008  (delta phase A-B) to phase A output  981 . In like manner, phase B may be fed through controllers  1005  and  1006  (delta phase A-B) and controllers  1011  and  1012  (delta phase B-C) to phase B output  982 , and phase C may be fed through controllers  1009  and  1010  (delta phase B-C) and controllers  1003  and  1004  (delta phase C-A) to phase C output  983 . Compare this embodiment to the other three phase delta power controller of  FIG. 31 . 
     FIG. 9  illustrates an alternate embodiment of the power converter of the invention. It is particularly well adapted for higher power (100 A and up) applications. It is in most respects the same as that shown in  FIG. 5 , except for the arrangement of switches Q 1 -Q 4 , and a different switch diode arrangement. Q 1 -Q 4  are independently controlled as before (logical control direct to the gate of each switch, no two gates tied together or receiving control from the same logical controller element), but the switch sources of respective switch pairs (i.e. Q 1 -Q 2 ) are not directly tied together, as they are in the embodiment in  FIG. 5 . Diodes D 1 -D 4  are also differently placed, rather than simply connected across source and drain of their respective switches. Additional diodes D 5 -D 8  are relatively small and inexpensive, and added to the design to help bypass the switches as they (diodes D 1 -D 4 ) turn off, but are not necessary when MOSFET switches are used (instead of the preferred IGBT&#39;s). 
   In a power factor correction application, the converter circuit of the invention can interface between the power line and a PFC capacitor, and/or reactor. If the power factor, or the phase delay, on the line is measured, and then fed into an appropriate error amplifier, of such design as will be readily available to those skilled in the art, then the power controller with its control circuitry may automatically correct power factor on the line, even approaching unity PF, and with response time on the order of 0.1 seconds. 
     FIG. 10  shows such an automatic variable power factor corrector  600 , having a power controller  100  and power factor correction capacitor(s)  630  and control circuitry. This topology is well adapted for correcting lagging power factor due to use of motors and transformers on the line. 
   Operation of automatic power factor corrector  600  is based upon the addition of a variable leading load in parallel with the lagging load to be corrected. The two loads may cancel each other out, achieving a unity power factor. This may be accomplished by varying controller  100  output into PFC capacitor(s)  630 , so that the varying output voltage in turn may vary output current into capacitor  630 , so that a variable capacitive load may be reflected back into the power line. Automatic correction may be achieved by adding a current sensor  641  in series with the load. A current sense signal  671  from current sensor  641  may be compared with a voltage signal  672  to detect phase delay (and thus power factor) in phase delay detector  620 . A phase error amplifier  650  may receive this phase delay information  673  and adjusts power controller  100  through its modulator  170  to vary reflected capacitance, and thus minimize phase delay (bringing PF toward unity). This loop preferably has a bandwidth of 20 Hz or less. (Power controller  100  is shown as a dotted block with its modulator  170  drawn as though separate to emphasize its function in this illustration.) 
   PFC capacitors can resonate with other elements in the power system. To limit or eliminate this possibility, an optional additional current sensor  642  is placed between controller  100  output and PFC capacitor  630 , in series. Within current sensor  642 , the fundamental line frequency may be filtered out, as will be appreciated by those skilled in the art, to leave only harmonic currents information. Current sense signal  674  containing this harmonic information may then be sent to a fast error amplifier  660  (several KHz bandwidth) which in turn may adjust modulator  170  of power controller  100  to keep the capacitor current sinusoidal (non-harmonic). Thus power controller  100  may respond to slow signals from power factor error amplifier  650 , and fast signals from harmonic error amplifier  660 . The result is an automatic power factor corrector  600  with continuous variability and which does not tend to resonate with other elements in a power distribution system. 
   The disclosed PFC method and apparatus can also be configured for three phase PFC for effecting balanced loads by employing two power controller units  100   a  and  100   b , and three PFC capacitors  630   ab ,  630   ac  and  630   bc  as shown in  FIG. 11 . In this embodiment, power controller  100   a  may be in parallel between a first AC line (A) and a third AC line (C), and power controller  100   b  may be in parallel between a second AC line (B) and the third AC line. Capacitor  630   ac  may be connected between the output of controller  100   a  and AC line (C), capacitor  630   bc  may be connected between the output of controller  100   b  and AC line (C), and capacitor  630   ab  may be connected between the output of controller  100   a  and the output of controller  100   b.    
     FIG. 12  shows a configuration for controlling three phase induction motor  612 , as an alternate PFC correction method accomplished by lowering the motor terminal voltage via controllers  100   a ,  100   b  when motor  612  in not operating at full load. Power controller  100   a  may be in series in line  1 , and power controller  100   b  may be in series in line  3 . Both controllers may return to line  2 . Independent modulation and control of controllers  100   a ,  100   b  may result in optimal power conversion and control for induction motor  612 , and may also optimize power quality on the three phase line system. 
   The power controller  100  of the invention is also well-adapted to be used in combination with simple componentry to fashion fully (and optionally automatically) adjustable components, such as capacitors, inductors, resistors, and the like, for example as shown in  FIGS. 13 ,  14 , and  15 . 
   In  FIG. 31 , a three phase delta power conditioner is shown in block diagram form. It is a combination of three power controllers of the invention and three transformers, which together implement a circuit for controlling the output voltage of a delta wired three phase input. Each power controller may be connected between two different phases and each controller divers a transformer which may modify the voltage on two different phases. Put differently, each phase may be acted upon by two different converter/transformer combinations. 
   As an illustrative example, regard phase A IN  971  in  FIG. 31 . Power controller  992  is connected between phase B and Phase A and drives transformer  962 . Power controller  991  is connected between phase A and Phase C and drives transformer  961 . The primary return of transformer  962  is connected to phase A IN  971 , and the autotransformed tap of transformer  962  is in turn fed to the floating winding of transformer  961 . The output of the floating winding of transformer  961  is then fed to the output as phase A OUT  981 . 
   Now under normal operating conditions, all controller outputs start at zero output voltage. In this mode, phase A may pass through transformer  962  and transformer  961  unmodified. However, as power controller  991  and power controller  992  increase their output, phase A may begin to be modified. Increasing output voltage from power controller  992  through transformer  962  may move the output tap of transformer  962  closer to phase B. Similarly, an equal increase in the output voltage from power controller  991  through transformer  961  may move phase A OUT  981  an equal distance toward phase C. The result of these two vectors is that phase A OUT  981  may be reduced in amplitude but may remain in phase with phase A IN  921 . 
   A like effect upon phase B and phase C will be appreciated, so that the overall effect may be an adjustable delta voltage source, concentric with the input voltage, and in phase with it. If the controllers are independently adjusted, then input phase angle irregularities may also be compensated for, which reduces voltage imbalance losses in three phase motors and transformers. 
   For operation from no output voltage to full output voltage, the turns ratio of each transformer primary to its autotransformed tap and floating winding is 3:1:1. Numbers higher than this (such as 6:1:1) may result in a smaller range of voltage adjustability and may reduce the required output current from each power controller. 
   In an alternate embodiment, each of the three power controllers is connected to a different input phase and provides an output that is between 0% and 100% of the input voltage (i.e., between IN and RETURN). Each output may drive the primary of its own transformer, where each such transformer may have an autotransformed tap that may be fed into the auxiliary winding of the transformer that is connected to the adjacent phase. The output of that auxiliary winding may then be the conditioned output of the phase for that transformer. 
   For the full range output from 0V to the full input voltage, the turns ratio of the transformer is:
 
 N (primary)=3 N (tap)=3 N (auxiliary)
 
where N(primary) is the number of total turns from the output of the power controller to its return, and it includes the turns in the tapped winding.
 
   Operation over different ranges is possible by varying the transformer turns ratio, as long as the tap and auxiliary windings all have the same number of turns. It will be appreciated therefore that output voltage is at a maximum (approaching the input voltage) when all power controllers are at minimum output voltage. Conversely, output voltage is at a minimum when all power controllers are at maximum output voltage. 
   Generally speaking, it will be preferred to operate all three power controllers at equal output voltages; however, since they may all three be individually controlled, the conditioner can be used to compensate for voltage imbalance on the input. 
     FIG. 13  shows adjustable capacitor  510 . Power controller  100  may variably reflect the capacitance of capacitor C 1  back onto the input and return connections. The reflected capacitance value ranges between 0 and the full rated value of C 1 . Typical applications would be adjustable power line filters with variable frequency and amplitude characteristics, and adjustable components of harmonic current traps and rejecters. See discussion infra of  FIGS. 24 and 25 . 
     FIG. 14  shows adjustable inductor  520  whose reflected inductance can be varied, via controller  100 , between the full rated value of L 1  and (theoretically) infinity. Its applications are as complementary components to the variable capacitor in its applications as disclosed above. It should be noted that for a duty cycle D and a full rated inductance L, reflected inductance is given by the formula:
   L   refl   =L/D   2    
     FIG. 16  shows variable resistor  530  with a resistance value adjustable, via controller  100 , between R 1  and (theoretically) infinity. This topology may have applications including motor controls, a variable damping element in power line filters, and variable AC/DC power loads for testing electrical equipment (transformers, generators, AC power supplies, inverters, power distribution systems, and the like). 
     FIG. 15  shows adjustable harmonic rejector (shunt filter)  550  with controller  100 . Inductor L 1  is connected between the output of controller  100  and the return, while capacitor C 1  is connected between output and input of controller  100 . As controller  100  duty cycle is increased, both reflected capacitance and inductance may decrease. The result is a parallel LC filter with resonance (or “notch”) that may be tunable over a wide frequency range. This may have application in power line harmonic voltage and current reduction. For instance, the unit could be installed in series with the power line and its resonance adjusted to reject a desired harmonic. In response to changes of load on the system, it may be suitably readjusted, either manually or automatically, for optimum performance. 
     FIG. 17  shows AC power conditioner  700  for regulating output voltage over a limited range. This configuration may allow use of a lower voltage power controller than one otherwise required for operation over a larger voltage range. 
   Input voltage may be fed to autotransformer  702  having two output taps  704 ,  706 . Lower tap  706  may be configured to be the lowest desired voltage step down, while higher tap  704  may be set for the highest desired voltage step up. Power controller  100  may be connected between these two taps and thus may vary the output voltage from one tap to the other in continuously variable increments. Conditioner/converter  700  may thus be used either as a constant output voltage regulator for input voltages that vary, or as a device for providing varying output voltages from a constant input voltage. 
   Using this configuration, if an output variation range of +/−20% is desired, then power controller  100  itself need only withstand 40% of the input voltage. This may allow available semiconductors to regulate much higher output voltages than if the controller  100  were operating without autotransformer  702 . In lower voltage circuits (such as 120 VAC), it may allow inexpensive low voltage semiconductors (&lt;100 VDC) to be used, giving significant cost advantages over other line conditioning methods. 
     FIG. 18  shows isolated output AC power conditioner  710  having power controller  100  and three part coupled magnetic structure  720 . This topology may provide isolated variable output voltage over a limited output range and may also provide galvanic isolation from input to output. 
   Magnetic structure  720  may comprise three core sections which are coupled at each end. Each section has associated winding  722 A,  722 B, and  722 C respectively, each winding having a number of turns N A , N B , and N C  respectively. For operation within the saturation limits of the core, voltages V may be applied to the windings according to the following formula:
 
 V   A   /N   A   +V   B   /N   B   +V   C   /N   C =0
 
while the corresponding formula for current is:
 
I A N A =I B N B =I C N C  
 
   In this isolated output AC power conditioner, input voltage may be applied directly across winding  722 A. Power controller  100  may receive the same input voltage and may apply a variable voltage across winding  722 B with the number of turns N B  corresponding to the maximum amount of output voltage regulation range desired. The voltage delivered from the output winding  722 C can be described therefore by the following formula:
 
 V   out   /N   C   =−V   in   /N   A   −V   controller   /N   B  
 
   With this topology, N B  can be much greater than N A  as the output regulation range is reduced. Thus power controller  100  output current may be reduced for a given total conditioner  710  output current (and power), and line regulation over the desired range may be accomplished with a relatively smaller power regulator  100 . Costs may thus be reduced, efficiency may be increased, and larger amounts of power may be regulated than by merely cascading a power controller with a standard isolation transformer. Applications for this topology may be in line voltage regulation, data processing, telecommunications, and medical equipment. 
     FIG. 19  shows high voltage input AC power conditioner  730 . The circuitry is substantially the same as for  FIG. 18  above, except that power controller  100  may be operated from a voltage that is lower than the input voltage. Winding  722 A has tap  724  in it, which may create in effect a step down autotransformer for use by controller  100 . The tap voltage may be selected according to the voltage input limitations of power controller  100 . All other specification and operation may be the same as above. 
   This topology can regulate voltages far beyond what could be done with conventional power semiconductors employed in direct regulation. As an example, the input voltage can be as much as 13,200V, and yet regulation can be accomplished using nothing more than standard semiconductors (having ratings such as 1200V or 1700V). Applications may be in regulated distribution transformers such as those dropping distribution voltages down to 120/240 VAC for residential and commercial customers. 
     FIG. 20  shows AC hybrid power conditioner  740 , similar to AC power conditioner  700  disclosed above, except that it may be capable of connecting different taps  746   a - d  in autotransformer  742  to the input voltage. Output regulation may be generally accomplished in two steps. The first step may comprise selecting and connecting an appropriate tap  746   a, b, c , or  d  on autotransformer  742  to the input voltage. The tap may be selected so that the input  748  of power controller  100  may be higher than the desired output voltage and the return of power controller  100  may be lower than the desired output voltage. Connection may be accomplished using thyristor switches  746   a - d , and in a manner similar to connection in conventional tap switching line conditioners. 
   The second step may comprise modulating controller  100  to provide an adjustable output voltage that can be varied continuously between its input and return voltages. By combining these steps, precise regulation of output voltages may be possible over a wide range of input voltages. This circuit topology may allow controller  100  to operate over a smaller voltage range so that lower voltage power controller components may be employed for a given output voltage. At the same time, continuous output adjustability may be maintained, providing superior regulating capability over conventional power conditioners. 
     FIG. 21  shows hybrid isolated AC power conditioner  750 , similar to high voltage input AC power conditioner  730  disclosed above, particularly in that it uses a three part magnetic structure  720  and power controller  100 , but it adds tap selecting capability to the winding  722 A. Tap connection may be accomplished using thyristor switches  744   a - c  to connect the proper tap  746   a - c  of winding  722 A to the input voltage. This tap selection may allow a coarse adjustment of the output voltage in one or more discreet steps. Fine adjustment may be achieved by varying the voltage on winding  722 B by varying the output of power controller  100 . 
   With tap selecting capability in this embodiment of the invention, power controller  100  may only be required to regulate over a much smaller range than otherwise practical or useful, and the amount of power delivered by controller  100  to the transformer may be decreased. This may allow either a decrease in the size of the power controller, or an increase in the output capability of the conditioner system for a given size power controller. 
     FIG. 22  schematically illustrates AC voltage regulator  300  of the invention. This circuit employs two power controllers  100   a  and  100   b  that may drive opposite ends of a primary winding  311  of transformer  310 . Secondary winding  312  is in series with Input line (high). 
   Regulator  300  functions by using the secondary  312  output to either add to or subtract from the input voltage. Adding and subtracting may be controlled by separately modulating the outputs of controllers  100   a  and  10   b . There are three modes of operation. 
   In mode  1 , both controllers may be at zero output voltage. The transformer primary  311  may thus be clamped to no voltage, while the current may be allowed to pass through secondary  312  (and through the primary as reflected through the transformer). Zero primary voltage may translate to zero secondary voltage, and the input voltage may be thereby maintained from input to output with voltage neither added nor subtracted. 
   In mode  2 , controller  100   a  output may be increased over the output of controller  100   b  (preferably held at a minimum). In this mode, a variable amount of voltage from controller  100   a  on primary  311  may add a proportional voltage (according to turns ratio of primary to secondary windings) to the input voltage, and output voltage may be thereby effectively increased. 
   In mode  3 , controller  100   b  output may be increased over the output of controller  100   a  (now preferably at a minimum). In this mode, a variable amount of voltage from controller  100   b  on primary  311  may subtract a proportional voltage (according to turns ratio of primary to secondary windings) from the input voltage, and output voltage may be thereby effectively decreased. 
   For industrial level (460 VAC) voltage regulators, a +/−10% variability may be required. This would mean a transformer turns ratio (primary to secondary) in the specific circuit of approximately 10:1. With this circuit and conventional power semiconductor technology, it may be possible to provide regulation at power levels in excess of 1 MW per phase. 
     FIG. 23  schematically illustrates isolated AC voltage regulator  320  of the invention. Regulator  320  may be take utility distribution voltages and may provide isolated and regulated low voltage outputs for residential, commercial, and industrial applications. 
   In operation, input voltage may be applied to input winding  331  and may provide thereby most of the voltage that may be transformed to output winding  333 . Two power controllers  100   a  and  100   b  operate in accordance with the disclosure herein from a lower voltage tap  335  on winding  331 . Controllers  100   a  and  100   b  may be used to drive intermediate winding  332 , which may have several time the number of turns of winding  331 . Output winding  333  may have conventional neutral tap  338 . 
   The two power controllers may operate in essentially the same three modes as described in conjunction with the apparatus shown in  FIG. 22 . In total, the controllers may provide a small part of the total voltage transformed to winding  333  to effectively adjust output voltage up or down from nominal voltage value, or to clamp to the nominal value. Advantages of this circuit include continuous amplitude adjustability over the entire regulating range, and no mechanical contacts to wear out. 
     FIG. 24  schematically illustrates adjustable parallel harmonic filter  400  embodiment of the invention. Filter  400  is a system that employs the power controller  100  of the invention as a kind of adjustable capacitor, as more fully disclosed elsewhere herein. PFC capacitor  430  lies between the output of controller  100  and low side of load  410 . Inductor  420  lies between input high and controller  100  input. Controller  100  is in parallel with load  410 . 
   It is envisioned that filter system  400  may find use as a harmonic current trap, with the advantage of continuous adjustability of its resonant frequency. With continuous adjustability, filter  400  may be fine tuned for better performance and less ringing with other power line components. It may also be readjusted at any time in accordance with the changing line and load conditions in the electrical system. 
     FIG. 25  schematically illustrates adjustable series harmonic rejector  450  embodiment of the invention. Rejector  450  is a system application of the adjustable harmonic rejector  550  discussed in conjunction with  FIG. 15 , and which may function as a kind of adjustable parallel LC network. Inductor  420  lies between controller  100  input and output, while PFC capacitor  430  lies between controller  100  output and high side of load  410 . Controller  100  is in series with load  410 . Optional filter  460  is in parallel with load  410 . 
   Rejector  450  may be used to selectively reject any harmonic current in a system so as to keep it from conducting back to source. Rejector  450  may be optionally aided by addition of parallel filter  460  to absorb (or shunt) any rejected harmonic current. As with the adjustable parallel harmonic filter  400 , rejector  450  may be fine tuned for optimum performance and to accommodate changing power distribution conditions. Preliminary testing of prototypes of power controller embodiments of the invention have been very encouraging. In a test of a power factor corrector embodiment of the invention, a one horsepower pump (running dry, at minimum load, at maximum load), a window fan (at low, medium, high), and a radial arm saw (running idle) were tested, and input current was first measured without any attempt at power factor correction, and PF was noted. Then the corrector of the invention was applied to correct PF, and input current was again measured, and PF noted. The results are summarized in Table 5. All measurements were taken at 120 VAC, 60 Hz. 
   
     
       
         
             
             
             
             
             
             
           
             
               TABLE 5 
             
             
                 
             
             
                 
               Input 
                 
               Input 
                 
                 
             
             
                 
               Current 
               Power 
               Current 
               Power 
             
             
               Test Unit 
               with/o PFC 
               Factor 
               with/PFC 
               Factor 
               Comments 
             
             
                 
             
           
          
             
               1 HP pump 
               10.74 A 
               .365 
                5.31 A 
               .950 
               Dry 
             
             
                 
                 
                 
                 
                 
               operation 
             
             
               1 HP pump 
               14.16 A 
               .782 
               11.68 A 
               .986 
               pumping, 
             
             
                 
                 
                 
                 
                 
               min. load 
             
             
               1 HP pump 
               15.10 A 
               .853 
               13.72 A 
               .990 
               pumping, 
             
             
                 
                 
                 
                 
                 
               max. load 
             
             
               Window fan 
                 
               .649 
                 
               .988 
               Low, 93 W 
             
             
               Window fan 
                 
               .690 
                 
               .986 
               Medium, 
             
             
                 
                 
                 
                 
                 
               141 W 
             
             
               Window fan 
                 
               .694 
                 
               .985 
               High, 180 W 
             
             
               Radial saw 
                7.41 A 
               .281 
                3.15 A 
               .845 
               Running, 
             
             
                 
                 
                 
                 
                 
               idle 
             
             
                 
             
          
         
       
     
   
   These tests, while providing good numbers, highlighted the importance of proper treatment of resonances between the PFC capacitors and parasitic system inductances. The occurrence of this problem is well known. Most manufacturers of conventional PFC systems use an elaborate and expensive array of optional harmonic “traps” that have to be customized to a specific installation. Passive damping, as will be appreciated by those skilled in the art, can to some extent be built into a system to reduce harmonic currents. But active damping, which is preferred, yields better PFC results, increased efficiency, and reduced cost. In active damping, small signal control circuitry may be used to vary the duty cycle of the PWM in opposition to the harmonics, causing the power controller to reject the harmonics, and leading to yet higher PF. It is anticipated that it will also lead to reduced resonances in the utility service as well. 
   A second round of testing on the 1 HP motor, running at no load, was conducted to test and demonstrate PFC effectiveness of the power factor corrector of the invention with added capability for active damping.  FIG. 26   a  is an oscilloscope printout showing the line current waveform of the 1 HP motor running at no load. Input voltage is 120 VAC. In this test, PF was noted at below 0.4, with input current at 10.7 ARMS. The waveform shows slight distortion. Common oscilloscope settings for the tests in the FIG.  26  series were: auto edge trigger; edge; source=1; level=875.000 mV; and holdoff time=14.000 mS. 
     FIG. 26   b  is an oscilloscope printout showing the effect of the prototype invention PFC, but without any damping. Input current was substantially reduced to 4.8 ARMS. Significant resonance and current draw at the ninth harmonic (540 Hz) can be seen  FIG. 26   c  is an oscilloscope printout showing the results of adding a passive (and power consuming) damper into the circuit. Input current drops to 4.6 ARMS, and the ringing is somewhat diminished. 
     FIG. 26   d  is an oscilloscope printout showing the results of removing the passive damping and employing the prototype PFC&#39;s own active damping circuit. It can be seen that the ringing has been eliminated (though there remain in this screen traces of crossover glitches caused by polarity switching in the error amplifier). Some distortion remains on the waveform, this is believed to be the uncorrected distortion existing on the original motor current waveform. Input current is reduced to 4.3 ARMS, even lower than with passive damping applied. 
     FIG. 26   e  is an oscilloscope printout showing, for comparison purposes, the effect of both active and passive damping applied. In most respects the waveform is identical to the previous printout, but the passive damper clearly contributes to greater power consumption as the input current increases to 4.5 ARMS, without significant improvement in the waveform over active damping alone. 
   Better results than these however are anticipated at the higher voltages more common in industrial use. These tests were conducted at 120 VAC where IGBT and diode voltage drops are more significant in terms of percentage loss, than would be the case at the higher voltages. Also at 240 VAC and 480 VAC, there will be less converter loss per KVAR. Secondly, the tests were not conducted in a worst case resonance scenario; in an industrial plant with far less “clean” power, multiple motor and PFC resonant combinations typically create fuse blowing and PFC capacitor failures, and have much greater need for the kind of PFC demonstrated here. 
   Another test was performed as a comparison of a conventional SCR power control device with the invention power controller (sometimes also referred to in the table and graphs as an “MPC”).  FIG. 27  is a spreadsheet of comparative data on SCR performance vs. an invention prototype power controller. A prototype power controller in accordance with this disclosure was run, in “buck” mode, at 120 VACRMS from 100% to 0% of range. Both KW efficiency and KVA efficiency were noted, as well as both input and output KW, KVA, PF and % THD-rmsa. The SCR device was run over the same range. The results are summarized in the spreadsheet, and the trend of the data, at least in certain respects, is evident from reading the spreadsheet. While the SCR remains highly efficient throughout the range from 100% voltage to 0%, and the MPC declines at 50% then falls off badly below 20%, the MPC sustains high input PF to a much lower voltage (still 0.89 at 40%; the SCR falls below 0.9 around 85%), and maintains near unity output PF down to below 10%. Similarly, the MPC sustains lower input and output current draw throughout the range, and is sharply lower in % THD on both input and output sides. 
     FIG. 28  is a graph of relative efficiencies of conventional power control devices compared to the power controller of the invention, and  FIG. 29  is a graph of relative harmonics and power factor (for resistive loads) of conventional power control devices compared to the power controller of the invention. A study of both graphs together suggests that, while SCR&#39;s with their noted efficiency stay at the top of the graph in  FIG. 28 , they are clearly the worst in PF and % THD performance in  FIG. 29 . In  FIG. 28 , it is apparent that the KW efficiency of the invention (“MPC KW” in  FIG. 28 ) is quite close (above 90%) to that of the SCR down to 60% of range, and exceeds the efficiency of both inverters and linear supplies down to about 20% of range. In summary, the invention, as compared to conventional devices, has good efficiency, good power factor, and excellent harmonics (THD&lt;1%). 
     FIG. 36-46  describe another aspect of the invention, an HMI ballast. In a specific embodiment, the ballast uses a single common converter circuit  900  as shown in  FIGS. 37-46 . Specifically, the single common converter circuit employs the plurality switch modes shown in  FIGS. 37-46  to successively modulate one or more of a plurality of switches Q 1 -Q 6  and diodes D 1 -D 6 . Specifically, the circuit also contains inductor L 1 . Specifically, the single common converter circuit can operate as an inverter, a direct converter, or both an inverter and a direct converter. Thus, when AC power, DC power, or both types of power are provided to this embodiment, a substantially square AC wave and current output is provided. Specifically, this embodiment is used in conjunction with one or more hydrargyrum medium-arc iodide (HMI) lamps. 
     FIG. 36  shows the square wave mode operation of the HMI ballast. As shown, the HMI ballast operates as an inverter 25% of the time, thus inverting 25% of the power. Further, the ballast operates as a direct converter the other 75% of the time, thus converting 75% of the power. This figure also demonstrates how the HMI ballast transitions from one operational mode to the next throughout the sinusoidal cycle of alternating current. 
     FIG. 37  shows HMI lamp ballast operational mode  1 . Specifically, the ballast uses this mode of operation when the line voltage is positive and less than 20V. In this mode, switch Q 5  modulates, while current free-wheels through switch Q 4  and diode D 3 . Switches Q 4  and Q 1  are closed, while switches Q 2 , Q 3 , and Q 6  are open. 
     FIG. 38  shows HMI lamp ballast operational mode  2 . Specifically, the ballast uses this mode of operation when the line voltage is positive, greater than 20V and less than 100V. In this mode, switch Q 5  modulates, while current free-wheels through switch Q 1  and diode D 2 . Switch Q 1  is closed, while switches Q 2 , Q 3 , Q 4 , and Q 6  are open. The free-wheeling current pulls power out of inductor L 1 . 
     FIG. 39  shows HMI lamp ballast operational mode  3 . Specifically, the ballast can use this mode of operation when the line voltage is positive and greater than 100V. In this mode, switch Q 1  modulates, while current free-wheels through switch Q 4  and diode D 3 . Switch Q 4  is closed, while switches Q 2 , Q 3 , Q 5 , and Q 6  are open. 
     FIG. 40  shows HMI lamp ballast operational mode  4 . Specifically, the ballast can use this mode of operation when the line voltage is positive and greater than 100V. In this mode, switch Q 1  modulates, while current free-wheels through diode D 6 , if switch Q 4  is open. Switches Q 2 , Q 3 , Q 4 , Q 5 , and Q 6  are open. The free-wheeling current pulls energy out of V− Cap, increasing its charge. 
     FIG. 41  shows HMI lamp ballast operational mode—zero crossing transition from Positive (mode  1 ) to Negative (mode  5 ). Specifically, the ballast uses this mode of operation when the line voltage transitions from positive to negative. In this mode, switches Q 1 , Q 2 , Q 4 , Q 5 , and Q 6  open, and switch Q 3  closes. Current free-wheels through diode D 6  out of V− Cap, increasing its charge. As current in inductor L 1  stops, Q 6  begins to modulate and Mode  5 , as shown in  FIG. 42 , begins. 
     FIG. 42  shows HMI lamp ballast operational mode  5 . Specifically, the ballast can use this mode of operation when the line voltage is negative and greater than −20V. In this mode, switch Q 6  modulates, while current free-wheels through switch Q 3  and diode D 4 . Switches Q 2  and Q 3  are closed, while switches Q 1 , Q 4 , and Q 5  are open. 
     FIG. 43  shows HMI lamp ballast operational mode  6 . Specifically, the ballast uses this mode of operation when the line voltage is negative, less than −20V and greater than 100V. In this mode, switch Q 6  modulates, while current free-wheels through switch Q 2  and diode D 1 , when switch Q 3  is open. Switch Q 2  is closed, while switches Q 1 , Q 3 , Q 4 , and Q 5  are open. The free-wheeling current pushes power into inductor L 1 . 
     FIG. 44  shows HMI lamp ballast operational mode  7 . Specifically, the ballast can use this mode of operation when the line voltage is negative and less than −100V. In this mode, switch Q 2  modulates, while current free-wheels through switch Q 3  and diode D 4 . Switch Q 3  is closed, while switches Q 1 , Q 4 , Q 5 , and Q 6  are open. 
     FIG. 45  shows HMI lamp ballast operational mode  8 . Specifically, the ballast can use this mode of operation when the line voltage is negative and less than −100V. In this mode, switch Q 2  modulates, while current free-wheels through diode D 5 , if switch Q 3  is open. Switches Q 1 , Q 3 , Q 4 , Q 5 , and Q 6  are open. The free-wheeling current pushes energy into V+ Cap, increasing its charge. 
     FIG. 46  shows HMI lamp ballast operational mode—zero crossing transition from Negative (mode  5 ) to Positive (mode  1 ). Specifically, the ballast uses this mode of operation when the line voltage transitions from negative to positive. In this mode, switches Q 1 , Q 2 , Q 3 , Q 5 , and Q 6  open, and switch Q 4  closes. Current free-wheels through diode D 5  into V+ Cap, increasing its charge. As current in inductor L 1  stops, Q 5  begins to modulate and Mode  1 , as shown in  FIG. 37 , begins. 
     FIG. 47  shows an electrical circuit for use in another specific embodiment of the controller apparatus of the invention. The specific circuitry of this aspect of the invention uses eight switches, eight diodes, two inductors, an input filter, an output filter, and novel controlling circuitry. Each switch is preferably a solid state switch, and each is preferably a transistor, such as an IGBT transistor. 
   Though the embodiments of the present invention (see, e.g.,  FIG. 47 ) have eight switches and the embodiments described above have four switches (See  FIGS. 4-7   d ,  9 ), these embodiments may share a good deal of componentry and may operate in similar fashions, as described below. Thus, everything set forth above, especially including the portions herein describing the four-switch embodiments of the power controller (See  FIGS. 4-7   d ,  9 ), is equally applicable to the eight-switch embodiment of the power controller shown in  FIG. 47 . 
   A specific circuit for controlling power to reactive, resistive, or non-linear loads in accordance with  FIG. 47  comprises at least eight separately controlled unidirectional switches that are modulated according to the polarity of the line voltage according to a logic “box” such that some combination of the eight switches is always on, no matter what the polarity is, including the “zero cross” point of polarity change on the input voltage waveform. 
   During the “zero cross” point, the embodiment of  FIG. 47  acts in a similar fashion to the embodiment of  FIGS. 4-5 , such that the input and output of the circuit are effectively short circuited by the simultaneous conduction of the eight switches. More information on this operation and its effects can be found in the description of  FIG. 4  above. 
   In a specific embodiment, the logic “box” comprises a polarity detector  160  and a modulator  170 , each described in detail with reference to  FIG. 4  above, and control logic. This embodiment also contains input filter  120  described with reference to  FIG. 4  above. 
   Power stage  130   b  specifically comprises switches Q 1 -Q 8  and diodes D 1 -D 8 . Preferably, each switch is a solid state switching device, with a diode, poled to have a sense opposite to the switch, in parallel across the source and drain of the switch. The switches are preferably transistors, such as the IGBT transistors illustrated for Q 1 -Q 8 , though they may also be any of several other types, such as BiT, MOSFET, MCT or GTO. 
   Each of the eight IGBT switches Q 1 -Q 8  is separately controlled, though they form in combination a unique arrangement that, in conjunction with control circuitry described herein, provides four quadrant operation (as described with reference to  FIG. 4  above) and low switching losses. 
   In specific embodiments, the eight switches Q 1 -Q 8  are paired, and each pair, Q 1 -Q 2 , Q 3 -Q 4 , Q 5 -Q 6 , and Q 7 -Q 8 , have their sources (if switches are mosfets) or emitters (if switches are IGBTs) tied together, and each of the switches in a pair are poled in the opposite sense to each other. Alternatively, in some embodiments, each pair could have their drains (if switches are mosfets) or collectors (if switches are IGBTs) tied together. Specifically, the diodes of each pair of such switches are opposite in sense to each other, as illustrated. 
   This embodiment also contains output filter  140   b , which provides output averaging and filtering through inductors L 1 , L 2 , and capacitor C 2 . Output filter  140   b  contains similar elements and performs similar functions as output filter  140 , described with reference to  FIG. 4  above. 
   This embodiment also contains level shifting block  180   b . Level shift block  180   b  receives output signals from the logic circuitry, which are then shifted in voltage level to drive switches Q 1 -Q 8 . Level shifting block  180   b  contains similar elements and performs similar functions as level shifting block  180 , described with reference to  FIG. 4  above. 
   This embodiment also contains control logic block  190   b . Control logic block  190   b  contains similar elements and performs similar functions as control logic block  190 , described with reference to  FIG. 4  above. Specifically, control logic block  190   b  operates in a manner such that switches Q 1  and Q 7  in power stage  130   b  operate in a similar fashion to switch Q 1  in power stage  130 , as described with reference to  FIG. 4  above. Likewise, control logic block  190   b  operates in a manner such that switches Q 2  and Q 8  in power stage  130   b  operate in a similar fashion to switch Q 2  in power stage  130 , as described with reference to  FIG. 4  above. Similarly, control logic block  190   b  operates in a manner such that switches Q 3  and Q 5  in power stage  130   b  operate in a similar fashion to switch Q 3  in power stage  130 , as described with reference to  FIG. 4  above. Correspondingly, control logic block  190   b  operates in a manner such that switches Q 4  and Q 6  in power stage  130   b  operate in a similar fashion to switch Q 4  in power stage  130 , as described with reference to  FIG. 4  above. 
   In a similar fashion, control logic block  190   b  operates in a manner such that diodes D 1  and D 7  in power stage  130   b  operate in a similar fashion to diode D 1  in power stage  130 , as described with reference to  FIG. 4  above. Likewise, control logic block  190   b  operates in a manner such that diodes D 2  and D 8  in power stage  130   b  operate in a similar fashion to diode D 2  in power stage  130 , as described with reference to  FIG. 4  above. Similarly, control logic block  190   b  operates in a manner such that diodes D 3  and D 5  in power stage  130   b  operate in a similar fashion to diode D 3  in power stage  130 , as described with reference to  FIG. 4  above. Correspondingly, control logic block  190   b  operates in a manner such that diodes D 4  and D 6  in power stage  130   b  operate in a similar fashion to diode D 4  in power stage  130 , as described with reference to  FIG. 4  above. 
   Specifically, control logic block  190   b  contains eight OR gates  181 - 188 . Each OR gate  181 - 188  is fed by an output from polarity detector  160  through turn off delays  194 ,  195 . Each OR gate  181 - 188  is also fed by an output from duty cycle modulator  170  through turn on delays  192 ,  193 . OR gates  181 ,  183 ,  185 ,  187  each receive as a first input an inverted output from polarity detector  160  through turn off delay  194 . OR gates  182 ,  184 ,  186 ,  188  each receive as a first input a non-inverted output from polarity detector  160  through turn off delay  195 . OR gates  181 ,  182 ,  185 ,  186  each receive as a second input an inverted output from modulator  170  through turn on delay  192 . OR gates  183 ,  184 ,  187 ,  188  each receive as a second input a non-inverted output from modulator  170  through turn on delay  193 . The output from each OR gate, through appropriate level shifting in level shift block  180 , controls or drives one of eight switches Q 1 -Q 8 . 
   This embodiment also contains turn on delays,  192 ,  193 , and turn off delays,  194 ,  195 , each described in detail with reference to  FIG. 4  above. 
     FIG. 48  illustrates an alternative embodiment of the power converter of the invention. It is particularly well adapted for higher power (100 A and up) applications. It is in most respects the same as that shown in  FIG. 47 , except for the arrangement of switches Q 1 -Q 8 , and a different switch diode arrangement. Switches Q 1 -Q 8  are independently controlled as before, but the switch sources of respective switch pairs (i.e. Q 1 -Q 2 ) are not directly tied together, as they are in the embodiment in  FIG. 47 . Diodes D 1 -D 8  are also differently placed, rather than simply connected across source and drain of their respective switches. Additional diodes D 9 -D 16  are relatively small and inexpensive, and added to the design to help bypass the switches as they turn off, but are not necessary when MOSFET switches are used (instead of the preferred IGBT&#39;s). 
   The embodiment shown in  FIG. 47  provides one distinct advantage over other embodiments: it allows the polarity to be changed mid-cycle. Thus, the embodiment shown in  FIG. 47  can act to either buck or boost the input voltage, and can switch between bucking and boosting during a cycle, thus providing more control of the regulated output voltage. 
   In another embodiment, shown in  FIG. 49 , the polarity of the regulated output voltage can only be changed on a half-cycle basis. In  FIG. 49 , the change in polarity is accomplished using TRIACs  210 - 213 . If TRIACs  210  and  213  are on, the circuit shown in  FIG. 49  acts to boost the input voltage, while if TRIACs  211  and  212  are on, the circuit shown in  FIG. 49  acts to buck the input voltage. As a TRIAC will conduct until the current through it drops below a certain threshold value (such as the end of an AC half-cycle), changing of polarity using the circuit in  FIG. 49  may be limited in speed. 
   The embodiment in  FIG. 47 , however, is not limited by TRIACs, and can change polarity mid-cycle. The embodiment of  FIG. 47  operates to buck the input voltage if switches Q 1 , Q 2 , Q 7 , and Q 8  are on for greater than 50% of a given duty cycle. Similarly, the embodiment of  FIG. 47  operates to boost the input voltage if switches Q 3 , Q 4 , Q 5 , and Q 6  are on for greater than 50% of a given duty cycle. Thus, the power controller shown in  FIG. 47  can change polarity mid-cycle, giving more control over the voltage than given by the power controller shown in  FIG. 49 . 
   An electrical converter implemented with a high frequency (&gt;10 KHz) and using switchmode power conversion techniques achieves great advantage over existing circuits, including higher output, smaller size, light weight, lower cost, greater efficiency, electrically quieter operation, and better reliability. 
   In broad terms, the largest markets for the invention are related to electrical power quality products and electrical energy conservation products. At least half of the applications currently identified for the invention relate to improving the efficiency of, or cleaning up power problems caused by, electrical motors and/or motor drives. The Edison Electric Institute reports that there are one billion electric motors in the U.S. alone, and that they consume collectively nearly half of the total electricity consumed in the U.S. 
   In compliance with the statute, the invention has been described in language more or less specific as to structural features. It is to be understood, however, that the invention is not limited to the specific features shown, since the means and construction shown comprise specific forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims, appropriately interpreted in accordance with the doctrine of equivalents. 
   With regard to componentry and assembly methodology above referred to, but not otherwise specified or described in detail herein, the workings and specifications of such components and the manner in which they may be made or assembled or used, both cooperatively with each other and with the other elements of the invention described herein, to effect the purposes herein disclosed, are all believed to be well within the knowledge of those skilled in the art. No concerted attempt to repeat here what is generally known to the artisan has therefore been made.