Abstract:
An electronic brushless variable transformer. Variable autotransformers, use brushes, and as such, have moving parts requiring maintenance and periodic cleaning of the brushes. A variable transformer without brushes is advantageous in that it eliminates the cleaning and maintenance of brushes.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/831,068 filed Jun. 4, 2013, the contents of which are hereby incorporated by reference. This application is also a continuation-in-part of application Ser. No. 14/295,708, filed Jun. 4, 2104 and now issuing as U.S. Pat. No. 9,722,501, the disclosure of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This description relates generally to electronic transformers and more specifically to brushless variable transformers. 
       BACKGROUND 
       [0003]    An electronic transformer is an AC electronic component that will change, or transform an AC input voltage to a different output voltage level. An important characteristic of typical transformers is that circuitry connected to the primary is electrically isolated from circuitry connected to the secondary winding. An output voltage higher than the input voltage will generate a lower output current, and a lower output voltage will generate a higher output current. After accounting for losses in the transformer the power into the transformer is substantially equal to the output power produced. A transformer may have a first, primary winding upon a core, with a second winding, or secondary, also disposed upon the same core. The primary core to which an input voltage is applied, through electromagnetic coupling induces a voltage across the secondary. Accordingly the output voltage of a transformer may be changed by adding or removing secondary turns 
         [0004]    Alternatively, discrete voltages may be selected by attaching wires (taps) at various taps. The taps if connected to a rotary switch provide discrete, but variable output voltages. 
         [0005]    In an alternative construction a more continuous output voltage may be produced by allowing a conductor (typically a carbon brush), to slide over exposed turns of a secondary winding. Typically, a knob is provided, and turning it in one direction increases the voltage output, and the opposite direction decreases the output voltage. 
         [0006]    Transformers of this sort may be desirable in applications which require a variable voltage, such as light dimmers, welders, motor controls, audio applications, testing equipment at low and high end operating conditions, and the like. However, using a conventional transformer with a bulky core and two windings in such applications would not be practical. If electrical isolation is not needed a device called an autotransformer may be substituted for a transformer. It advantageously utilizes a single winding in which taps or brushes may be applied as previously described in a transformer. 
         [0007]      FIG. 1 . shows a schematic of an autotransformer  100 , which has a single winding  102  over a core material  104  with two primary terminals  106  and  108  at the extreme ends of that single, or primary winding. It also has one or more terminals or taps  110  at intermediate tap points along the single winding  102  that forms the secondary winding or circuit. Thus the primary and secondary coils have part or all of their turns in common. 
         [0008]    The primary voltage  112  is applied across two of the primary terminals, and the secondary voltage  114  taken from the tap terminals. The autotransformer almost always has one terminal  108 , in common with the primary voltage. The primary and secondary circuits, therefore, have a number of windings turns in common. Since the volts-per-turn is the same in both windings, each develops a voltage in proportion to its number of turns. In an autotransformer, part of the current flows directly from the input to the output, and only part of the current is transferred by induction. 
         [0009]    Autotransformers may also include many taps and include additional automatic switchgear to allow them to act as automatic voltage regulators to maintain a steady voltage over a wide range of load conditions. If a sliding tap is used that contacts more than one turn at a time, the turns are shorted. However if a resistance is inserted sliding tap the shorting problem may be eliminated. An autotransformer that is designed to produce continuous voltage variation, without shorting adjacent turns is known as a variable autotransformer, such as the VARIAC® variable autotransformer from Instrument Service and Equipment, Inc., Cleveland, Ohio. 
         [0010]      FIG. 2  shows an electrical schematic of a variable autotransformer. In a variable autotransformer, part of the winding coils  202  may be exposed and the secondary connection is made with a sliding brush  204 . The brush is typically a carbon brush. The primary connection is  206 . The addition of the brush, which may be controlled with an external knob (not shown) allows a continuously variable turns ratio to be obtained, which is established by the location in the winding the brush makes contact. This allows for very smooth control of voltage. The output voltage  208  is not limited to the discrete voltages represented by actual number of turns. The input voltage  210  can be smoothly varied between turns as the brush has a relatively high resistance (compared with a metal contact) and the actual output voltage is a function of the relative area of brush in contact with adjacent windings. The primary connection  206  can be connected to only a part of the winding allowing the output voltage to be varied smoothly from zero to above the input voltage. This allows a variable autotransformer to be used for testing electrical equipment at the limits of its specified voltage range. 
         [0011]    Brushes make physical and electrical contact in conducting electricity between moving parts and tend to wear from use. Typical applications of brushes include electric motors, alternators, electric generators, and variable autotransformers. Accordingly it would be desirable to eliminate the use of brushes in a variable transformer design. 
         [0012]    The voltage sensed by the switches  310 ,  312 ,  314 ,  316  is before the corrected output by T 1  This ensures that the input to T 1  is monitored and  310 ,  312 ,  314 ,  316  change to get desired voltage at the output of T 1   
         [0013]    Such commercially available devices for having variable voltages are typically constructed with transformer and moving brush. The brush is moved on the coil of the transformer to obtain variable AC voltage. The transformer with 2 phases has 2 brushes and transformer with 3 phases has 3 brushes moving simultaneously, manually or operated by motor. These devices are typically referred to as “Variac” or “Variable Transformer”. 
         [0014]    A disadvantage of this system of variable AC voltage is that the brushes are made of Carbon and they wear out. The mechanical moving parts and the brushes need regular maintenance. The motor operated Variacs have gears, limit switches etc. that also need regular maintenance. Moving brushes create arcing. Therefore, this cannot be used in hazardous locations. 
         [0015]    Those having skill in the art would understand the desirability of having a variable transformer that uses circuitry to vary and regulate output voltage without brushes. The variable transformer described herein allows the use of a variable transformer not requiring cleaning and maintenance of moving parts, nor mechanical brushes. 
       SUMMARY 
       [0016]    The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the invention or delineate the scope of the invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later. 
         [0017]    The present example provides an electronic brushless variable transformer using electronic switches and a unique circuitry to provide a variable voltage output. An electronic variable transformer without brushes is advantageous in that it eliminates arcing, the cleaning and maintenance of brushes. 
         [0018]    The Electronic version of a VARIAC® (electronic brushless variable transformer) described herein does not need the brushes, mechanical movement or a motor to produce a variable AC output. The Electronic VARIAC® can also be described as a “electronic brushless variable transformer”, “Solid State VARIAC®” or “Solid State Transformer” and they can be built for single, double or three phase operations. A buck/boost technique nay be applied to eliminate use of the moving parts in commercially available single, double and three phase Variacs used in low and high voltage applications. The electronic Variac can also be used to stabilize or regulate the output voltage. 
         [0019]    The human interface for the Electronic VARIAC® can be a simple potentiometer (for manual adjustment), digital switch or a touch screen or a tablet or iPhone, or the like (for remote adjustment). Many devices are being added to “IOT” (Internet Of Things) devices. If the Electronic Variac is installed in the hazardous zone, the remote control is the only option for setting. The remote access also helps to check the status of the output. 
         [0020]    Many of the attendant features will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0021]    The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein: 
           [0022]      FIG. 1  shows an electrical schematic of an autotransformer. 
           [0023]      FIG. 2  shows an electrical schematic of a variable autotransformer having carbon brushes contacting a winding. 
           [0024]      FIG. 3  shows an electrical schematic of a continuously variable autotransformer (electronic brushless variable transformer) utilizing switches rather than brushes. 
           [0025]      FIG. 4  shows an electrical schematic of the electronic brushless variable transformer with switches set in a first position wherein the switches are closed to create an increase in line voltage. 
           [0026]      FIG. 5  shows an electrical schematic the electronic brushless variable transformer with switches set in a second position wherein the switches are closed to create a decrease in line voltage. 
           [0027]      FIG. 6  shows an electrical schematic of the electronic brushless variable transformer with switches set in a third position wherein the output voltage equals the input voltage. 
           [0028]      FIG. 7  shows an electrical schematic of multiples of the electronic brushless variable transformer used in series. 
           [0029]      FIG. 8  shows a table with exemplary total voltage output variation for various switch configurations of the first example of an electronic brushless variable transformer. 
           [0030]      FIG. 9  shows a second example of an electronic brushless variable transformer. 
           [0031]      FIG. 10A-10D  show exemplary total voltage output variation for various switch configurations for the second example of an electronic brushless variable transformer. 
           [0032]      FIG. 11  is a process flow diagram illustrating a method of creating or setting a variable voltage output utilizing the electronic brushless variable transformers described herein. 
           [0033]      FIG. 12  shows the process for correcting the output of multiple cascaded circuits. 
           [0034]      FIG. 13  illustrates generally the use of the circuit to control each of the phases in a three phase power system. 
           [0035]      FIG. 14  is an exemplary network  100  in which the electronic brushless variable transformers described herein may be implemented. 
       
    
    
       [0036]    Like reference numerals are used to designate like parts in the accompanying drawings. 
       DETAILED DESCRIPTION 
       [0037]    The detailed description provided below in connection with the appended drawings is intended as a description of the present examples of a brushless variable transformer and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples. 
         [0038]    The examples below describe a brushless variable transformer. As those skilled in the art will appreciate, the present examples are suitable for application in a variety of different types of voltage control and regulation systems. 
         [0039]      FIG. 1  shows an electrical schematic of an autotransformer  100 . In this AC circuit a secondary voltage  114  less than the input voltage  112  is generated from a tap point  106  at a point in the winding  102 , which may include a ferromagnetic material  104  as a core. Such a device typically provides a fixed AC output voltage as the tap point  106  is typically a hard wired connection. 
         [0040]      FIG. 2  shows an electrical schematic of a variable autotransformer with carbon (or equivalent) brushes contacting a winding  200 . Here an output voltage  208  may be varied to a value less than that of the AC input  210  by the mechanically positioning of a typically carbon brush  204  along an exposed portion of a winding  202 . Here the brush, or brushes, are mechanically moved along contact points along the winding  201  to generate a lesser desired output voltage  208 . Brushes tend to wear and as a result are a maintenance item. Also, intricate mechanical couplings typically have to be provided to move the brushes along the winding, which is another maintenance item. 
         [0041]      FIG. 3  shows an electrical schematic of a unique brushless variable transformer (or equivalently an “Electronic Variac”, “Binary Variable Transformer” or “Brushless Variac”)  300  constructed as described herein. This circuit advantageously allows a variable AC voltage to be generated without the need for mechanical parts, couplings carbon brushes, or the like. Further the output voltage may be varied digitally, and remotely, either directly or through an intermediary controller  324 . Typically a remote interface such as provided on a tablet or other mobile device may be utilized. The areas of application of devices are increasing. People are looking for “IOT” (Internet Of Things” devices. Having remote access to Electronic Variac would be required in future. The Electronic Varaic could be installed in hazardous environment, Variac with brushes cannot used due to arcing. In this environment Electronic Variac would be ideal choice and remote access would be preferred. 
         [0042]    Importantly, as differing from the circuit of  FIG. 2 , here the voltage may be sensed by transformer at the source  308 . The voltage sensed by switches  310 ,  312 ,  314  and  316  will remain same before and after a voltage correction implemented by switching. Importantly the circuit here in  FIG. 3  includes switches that may be coupled on the input side of the transformer (next to source  318 ). 
         [0043]    The voltage sensed by the switches  310 ,  312 ,  314 ,  316  is after the corrected output by T 1 . This would affect the voltage seen by  310 ,  312 ,  314 ,  316  change when they are switched. 
         [0044]    For many years silicon controlled rectifiers (“SCRs”) have been used for voltage regulation. The circuits described herein allow regulation without an SCR being in the line all the times, advantageously allowing circuit designers to work with higher voltage and more reliability, and further providing the ability to dial in, or set, a specific voltage. Finally the circuits tend to have a fast step response. The step response is typically 30 milli seconds. 
         [0045]    A conventional transformer  302  has a primary winding  304  and a secondary winding  306  sharing a common core  308 . Voltage is induced in the secondary winding  306  solely by inductive coupling to the primary winding  304 . The transformer  302  is characterized by the ratio of the number of turns of the primary winding  304  around the common core  308  to the number of turns of the secondary winding  306  around the common core. 
         [0046]    Power switches  310 ,  312 ,  314 , and  316  are conventionally constructed switches, and may be of any suitable construction. These switches may be relays, contactors, or solid state power devices such as insulated gate bipolar transistors (IGBT) and silicon-controlled rectifiers (SCR), which are also known as thyristors. The switches are isolated from the line current, and operate at much lower voltage than line voltage. Alternating current (AC) at line voltage is provided at an input  318 , and modified alternating current at variable voltage is at an output  322 . The line voltage may be low, in the range of 200 to 400 VAC, or may be in a medium voltage range of 4600 to 13,600 VAC. The circuit is provided with a neutral connection  320 . The Brushless Variac system includes a set of transformers and its associated switches and has one controlling element, which could be a microcontroller, a PLC, or equivalent. 
         [0047]    Switches  310 ,  312 ,  314 , and  316  are not operated at line voltage, and may be controlled using an intermediary controller such as microcontrollers and/or a programmable logic controllers (PLC)  324  using proportional-integral-derivative control (PID) and or a microcontroller, or the like. The construction and wiring of such controllers is well known and is not shown in  FIG. 3  for simplification of the diagram. Online control of the PLC is also provided by controlling the PLC through a conventional computer network (not shown) coupled to the PLC, which may include tablet computers, notebook computers and the like configured as control panels. 
         [0048]    The methods for implementing and controlling a brushless variable transformer as described herein are unique to the examples described below. Power switches  310 ,  312 ,  314 , and  316  can be configured to allow or prevent current from passing through them, and subsequently alter the direction of current applied to the secondary winding of transformer  302 , thereby making the output voltage buck or boost due to changes in the inductive voltage transfer from the secondary winding  306 . The various switch configurations and subsequent variation in the output voltage are described in  FIGS. 4-6 . 
         [0049]      FIG. 4  shows an electrical schematic of a brushless variable transformer wherein the switches are opened or closed to create an increase in line voltage. The controller  324  directs the switches  310  and  316  to allow current to flow through them, and switches  314  and  316  not allow current to pass. Input alternating current  318  passes through the primary winding of transformer  302 . Arrow  502  shows the direction of current flow. Simultaneously, the condition of switches  312  and  316  allow current from input  318  to pass through the secondary winding  306  of transformer  302  to neutral  320 . Arrow  504  shows the direction of current flow in the secondary winding. The condition of switch  316  connects the circuit to the neutral  320 . 
         [0050]    Inductive coupling of the primary and secondary windings in this example provides for an increase in the voltage at the circuit output  406 . The magnitude of the output depends on the ratio of the number of wire turns in the primary winding  304  to the number of wire turns in the secondary winding  306  in transformer  302 . If, for example, when the secondary winding of transformer  402  is wound to produce 1% of the output, the output voltage  406  will equal the input voltage of the input current  318  plus 1%. 
         [0051]      FIG. 5  shows an electrical schematic of the present invention wherein the switches are configured to create a decrease in line voltage. Here, the controller  324  activates switches  312  and  314  to allow current to flow through them, and switches  310  and  316  not to allow current to pass. Input alternating current  318  passes through the primary winding of transformer  302 . Arrow  502  shows the direction of current flow. Simultaneously, the condition of switches  312  and  314  allow current from input  318  to pass through the secondary winding  306  of transformer  302  to neutral  320 . Arrow  504  shows the direction of current flow in the secondary winding. The condition of switch  314  connects the circuit to the neutral  320 . 
         [0052]    Inductive coupling of the primary and secondary windings in this example provides for a decrease in the voltage at the circuit output  506 . The magnitude of the output depends on the ratio of the number of wire turns in the primary winding  304  to the number of wire turns in the secondary winding  306  in transformer  302 . If, for example, when the secondary winding of transformer  302  is wound to produce 1% of the output, the output voltage  506  will equal the input voltage of the input current  318  minus 1%. 
         [0053]      FIG. 6  shows an electrical schematic of the present invention wherein the output voltage equals the input voltage. Here, switches  314  and  316  are activated by the controller  324  to allow current to flow through them, and switches  310  and  312  do not allow current to pass. Input alternating current  318  passes through the primary winding of transformer  302 . Arrow  602  shows the direction of current flow. Simultaneously, the condition of switches  310  and  412  do not allow current from input  318  to pass through the secondary winding  306  of transformer  302 . As such, there is no current to provide inductive coupling to the current passing through the primary winding  602  and its voltage remains unchanged from the voltage of the input current  318 . 
         [0054]      FIG. 7  shows an electrical schematic of multiples of present invention used in series. For simplification of the diagram, the controller for the switches is not shown. Although an exemplary pair of circuits  300  and  700  providing brushless variable transformers are shown, it is obvious to those skilled in the art that a plurality of such circuits can be connected in series to provide a wide range of possible voltage outputs. Each brushless variable transformer circuit can be provided with a different ratio of the number of wire turns in the primary windings to the number of turns in the secondary windings providing a wide range of possible outputs. 
         [0055]    When multiple circuits shown above are coupled, or cascaded in series, the amount of buck (decrease in voltage) or boost (increase in voltage) can be controlled to get desired voltage at the output. In  FIG. 7 , two circuits  300  and  700  are coupled in series with different primary winding to secondary winding turns ratio transformers  302  and  702 . The output current  322  from circuit  300  is the input current  750  to circuit  700 . 
         [0056]    If, for example, transformer  302  provides an exemplary 1% variation in the output current  322  voltage, there are three possible conditions transformer  302  can effect on the output current. These are +1%, −1%, and 0%. The +1% condition occurs when the switched in the circuit  300  are as shown in  FIG. 4 , −1% occurs when the switches in circuit  300  are as shown in  FIG. 5 , and 0% when in the switches are as shown in  FIG. 6 . 
         [0057]    Similarly for circuit  700 , if the ratio of the primary winding  706  turns to the secondary winding  708  are such that the transformer  704  provides an exemplary 3% variation, the three conditions circuit  700  can effect on the input current is +3%, −3%, and 0%. By linking the circuit  300  and circuit  700  in series such that the output current  322  is also the input current  750  to circuit  700 , the voltage variation range is +/−4%. 
         [0058]    By simultaneously activating with a controller, the switches  310 ,  312 ,  314 ,  316  and  710 ,  712 ,  714 ,  716  on the brushless variable transformer circuits  300  and  700  can be positioned to allow or not allow current to pass. An example of the possible voltage variations possible for this example is shown in  FIG. 8 . 
         [0059]      FIG. 8  shows a table with exemplary total voltage output variation for various switch configurations for the exemplary variable transformers shown in  FIG. 7 . With two circuits with transformer  302  providing +/−1% of variation and transformer  704  providing a variation of +/−3%, it is possible to vary the output voltage of the cascade from −4% to +4%. Column  802  of  FIG. 8  shows the possible effects on the input current voltage provided by circuit  300  in  FIG. 7 . Column  804  shows the possible effects on its input current voltage provided by circuit  700  in  FIG. 7 . Column  806  shows the total variation in voltage provided by the two circuit operating in series as shown in  FIG. 7 . 
         [0060]    For the positive values in each of column  802  and  804 , the switches are configured as shown in  FIG. 4 ; for negative values, the switches are configured as shown in  FIG. 5 , and zero values occur when the switches are as shown in  FIG. 6 . By varying the switch positions systematically using the controller, total output variation in column  806  can be varied from +4 to −4%. 
         [0061]    The examples provided above are but exemplary, and not limiting. The basic circuit may be varied in construction as long as a buck and boost may be applied to the output, causing a controlled variation without use of brushes. Alternatively the cascaded configurations and their ratios of primary winding turns to secondary winding turns may be adjusted to produce a variety of outputs. 
         [0062]    For example, it is possible to couple more stages and get output variation of −31% to +31%, or −46% to +46%. If additional precision is required, additional stages of ½% or ¼% could be added. Similar stages may be constructed for use in three phase input/output needs. 
         [0063]      FIGS. 9 and 10  show a second example of an electronic Variac with various conditions of switches SW 1  through SW 4 . The reference designations utilized in  FIG. 9  are also applicable to  FIGS. 10A-10   10 D which show the switches in various open or closed states to achieve the desired output voltages of  FIG. 11 . Circuit nodes are numbered 1-5 in the solid black circles. The input is applied across nodes  1  and  2 , and the output is taken across nodes  5  and  2 . A first terminal of SW  1  is coupled to node  2 , as is a first terminal of SW  2 , and a secondary first terminal of T 1 . A second terminal of SW 1  is coupled to node  3  as is a first terminal of SW  3 , and a first terminal of the primary of T 1 . A second terminal of SW  2  is coupled to node  4 , as is a first terminal of SW  4 . A tap on the primary of T 1  is coupled to node  2  as is a second terminal of SW  4  and a second terminal of SW  3 . A second terminal of the secondary winding of T 1  is coupled to node  5 . As is known to those skilled in the art a conventional controller  324  is coupled to SW  1 -SW  4  to control their operation (open or closed), and configured to measure voltages and other circuit states in the circuit so that the output voltage may be set or otherwise controlled. Controller  324  may be provided with a wired, or wireless link to a remote device such as a tablet, smartphone or the equivalent  350  to control the circuit  900 , and to read the circuit state including the output voltage. Switching devices SW  1 -SW  4  are conventionally constructed and may be electronic, mechanical, electro-mechanical devices, or equivalent. Transformer T 1  is conventionally constructed and may include a core. Transformer T 1  may include a primary winding having a first and second terminal and a tap, Transformer T 1  may also include a secondary winding having a first and a second terminal. 
         [0064]      FIG. 10A-10D  show exemplary total voltage output variation for various switch configurations for the second example of an electronic brushless variable transformer. 
         [0065]    In  FIGS. 9 and 10A -D the T 1  primary has center tap. The controller  324  measures the input voltage. In  FIG. 10A  SW  1 -SW  4  are off (Off=open, and ON=closed as used herein) causing the output voltage to equal the input voltage. 
         [0066]    As seen in  FIG. 10B  when the controller  324  finds that the input voltage is higher than the tolerance, then it turns on SW 1  (SW 2 , SW 3  and SW 4  are off). This action causes the output voltage to decrease by the amount equal to the secondary voltage of T 1 . 
         [0067]    As seen in  FIG. 10  D when the input voltage is within the tolerance then switches SW 3  and SW 4  (SW 1  and SW 2  are off) are turned on, In this case input voltage is equal to the output voltage. 
         [0068]    As shown in  FIG. 10C  when the controller finds that the input voltage is lower than the tolerance then it turs on only SW 2  (SW 1 , SW 3  and SW 4  are off). This action causes the secondary voltage of T 1  to be added to the input voltage. 
         [0069]    In alternative examples several sets of this circuit  900  are connected in series. Each set reducing the its output voltage to a lower tolerance that can be corrected by the subsequent stage. 
         [0070]    The second example of an electronic brushless variable transformer may also be configured as previously described to provide a variable AC voltage in two phase, three phase and the like AC power distribution circuits. In a further alternative example, the same principal is used in 2 or 3 phase circuits to accomplish required output voltage within tolerance in all phases. 
         [0071]    The circuit  900  may be adjusted by configuring the switches in  FIGS. 10A-10D  to increase decrease or maintain a desired voltage. Under guidance of the controller  324  the circuit configurations may be set to obtain a desired output voltage in according to the following process. 
         [0072]      FIG. 11  is a process flow diagram illustrating a method of creating a variable voltage output utilizing the electronic brushless variable transformers described herein  1100 . At block  1101  the voltage at the input of transformer T 1  (of  FIGS. 9 and 10 ) is measured. At block  1103  a decision is made by comparison of the voltage to a predetermined level (the level may be adjusted or in alternative examples dynamically adjusted). If the voltage at T 1  is within tolerance the circuit switches are set so that the output voltage is equal to the input voltage at block  1105 . If the voltage measured at T 1  is higher than the preset voltage level the switches are adjusted so that the circuit output is equal to the input voltage minus the secondary voltage of T 1 . And finally if the Voltage at the input of T 1  is lower than the preset threshold then the switches are adjusted so that output is equal to the input plus the secondary voltage of T 1 . The process may be set to repeat as many times as desired to provide a desired level of voltage, or control of the voltage at the circuit output. 
         [0073]      FIG. 12  shows the process for correcting the output of multiple cascaded circuits ( 900  of  FIGS. 9 and 10 )  1200 . The corrections of  FIG. 11  may be successively applied to progressively control the output voltage  1207 . Here the first correction process  1201  provides voltage output of this stage that is within a maximum tolerance range. At block  1203  a second cascades circuit is controlled to provide a moderate range of tolerances. And finally at block  1205  a third stage is controlled to produce an output within the minimum tolerance level. A sued herein maximum, moderate, and minimum are used to denote a progression of control from coarse to fine that may be set at the discretion of a user. Also more or fewer circuits may be cascaded as desired to produce a desired level of output voltage control. 
         [0074]      FIG. 13  illustrates generally the use of the circuit ( 900  of  FIGS. 9 and 10 ) to control each of the phases in a three phase power system. Control of each phase may be achieved by single, or cascaded circuits to provide the desired control. Each circuit controls the output of its phase independently of the other circuits. The overall control for 1 and 2 phases is achieved using a single microcontroller or PLC (Programmable Logic Controller). For 3 phase units  2  or three microcontrollers/PLCs are used. They communicate with each other on communication lines (wired or wireless) so that overall objective is achieved. One of the microcontroller/PLC may be tasked with communicating with the outside world using the Ethernet port or equivalent. 
         [0075]      FIG. 14  is an exemplary network  1400  in which the electronic brushless variable transformers described herein may be implemented. A direct link may be made to the intermediary controller  324  by a computing device such as a smart phone, tablet, laptop, PC, dedicated terminal or the like. Typically code for controlling the electronic brushless variable transformer components resides in the intermediary controller, with it providing an interface to a more conventional computing device (typically through an “APP” or “Application” located remotely and controlling it through a wired, wireless, or a combination of wired and wireless connections, of which examples are provided below. 
         [0076]    Computer  1415  may be a server computer coupled to a user&#39;s computer  1420  through a conventionally constructed local area network  1425 . The intermediary controller  324  that controls the electronic brushless variable transformers described herein may be interfaced with this computer in order to communicate (sending and receiving) in various ways with it by remotely located control devices  1401 ,  1450 ,  1440 ,  1415 , 120 . The connections shown are exemplary and those skilled in the art will realize that a variety of wired and wired interfaces may be used to control the electronic brushless variable transformer. 
         [0077]    In the local area network the user&#39;s computer is typically part of the local area network  1425  which may include a plurality conventional computers (not shown) and conventional peripheral equipment (not shown) coupled together utilizing topologies (token, star and the like) and switching equipment known to those skilled in the art. Those skilled in the art will realize that other processor equipped devices such as tablets, smartphones, cellular telephones, appliances and the like may be coupled to the internet utilizing conventional techniques known to those skilled in the art. 
         [0078]    A typical local area network  1425  may include a conventionally constructed ISP network in which a number or plurality of subscribers utilize Wireless connections including cellular data, telephone dial up, DSL, cellular telephone, cable modem, or the like connections to couple their computer to one or more server computers  1415  that provide a connection to the world wide web  1435  via the internet  1430 . Typically the intermediary controller  324  may be coupled to a computer in the network  1420 . Which control the electronic brushless variable transformer  300  or  900 , which interfaces with tablet or the like  350 . Alternatively the tablet 35  may communicate with the network at other connection points. For example the tablet  35  might be at a remote location and provide control of the circuit  300  or  900  through the facility of the various communication channels described in  FIG. 14 . 
         [0079]    Wide area network, or world wide web  1435  is conventionally constructed and may include the internet  1430  or equivalent coupling methods for providing a wide area network. As shown a conventionally constructed first server computer  1410  is coupled to conventionally constructed second server computer  1415  through a conventionally constructed internet connection to the world wide web  1430 . 
         [0080]    In a peer to peer network a Peer computer  1440  is conventionally constructed to couple to the internet  1430  utilizing peer to peer network technology. Peer computer  1440  may couple to a plurality of similarly connected peer computers in a peer to peer network (not shown), or to other computers  1401 ,  1420  that are part of conventionally constructed networks  1425 ,  1435 . 
         [0081]    In a conventional wireless network  1405  a conventionally constructed tablet, smartphone, laptop, PC computer or the like  1401  is coupled to the internet  1430  via a conventionally constructed wireless link  1445 . The wireless link may include cellular  1445 , and satellite technology  1455  to provide the link. Such a wireless network may include a conventionally constructed first server computer  1410 , typically provided to manage connections to a wide area network such as the internet. 
         [0082]    A conventionally constructed back link may be provided to efficiently provide an additional channel to couple to the internet. For example in situations where communication is one way in nature, the back link may provide communications in the opposite direction. An example would be viewing a listing of system status or voltage outputs on a separate monitoring device and sending desired device settings via telephone  1440 . Those skilled in the art will realize that back links may equivalently be provided by cellular telephones, cordless telephones, paging devices and the like. 
         [0083]    Those skilled in the art will realize that the process sequences described above may be equivalently performed in any order to achieve a desired result. Also, sub-processes may typically be omitted as desired without taking away from the overall functionality of the processes described above.