Abstract:
A method for performing power conversion provides a converter output AC waveform from a converter input AC waveform, the convertor input waveform having an input power level, an input frequency, an input waveform shape, and an input voltage/current characteristic. The converter input AC waveform is applied to a converter switch with a switch frequency and the switch is operated at the switch frequency to provide a switched waveform having a plurality of switched waveform notches with a notch repetition rate substantially equal to the switch frequency. A filter performs filtering of the switched waveform to provide the converter output AC waveform with an output power level substantially equal to the input power level, an output frequency substantially equal to the input frequency, an output waveform shape substantially similar to the input wave form shape, and an output voltage/current characteristic substantially different from the input voltage/current characteristic.

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of power conversion and in particular to the field of alternating current power conversion. 
     BACKGROUND OF THE INVENTION 
     It is well known to provide power converters for converting electrical power from one form into a different form that is useable under many specific circumstances for powering electrical load devices. For example, it is known to provide a direct current (DC) power supply that converts alternating current (AC) power into DC power for supplying DC electrical power to mobile devices. 
     Additionally, it is known to provide an AC/DC power conversion device which is adapted to perform the power conversion in accordance with the power sources available in different countries. Another well known type of power conversion is the AC/DC type of conversion that is performed by light dimmers, wherein the peak-to-peak voltage of the output is maintained substantially the same as the peak-to-peak voltage of the input while the power conversion is accomplished by changing the duty cycle of the output. 
     Commercial power in Europe is supplied at 220 VAC with a frequency of 50 Hertz (Hz). In the United States the standard voltage supplied is 120 VAC at 60 Hz. In addition, brownouts may significantly reduce a line voltage below the standard level and, conversely, lighter loads, particularly at night, may cause the line voltage to increase above the standard level. Additionally, corresponding variations in frequency are possible. Accordingly, power converters operating on the standard power suppliers to provide a DC source are typically designed to operate at frequencies between 47 and 65 Hz and with voltages ranging from 85 VAC to 265 VAC. 
     Typically such a DC power supply converts an AC input voltage to a DC output voltage using an electromagnetic interference filter, a power factor correction circuit and a DC to DC converter. The electromagnetic interference filter is used in order to insure compliance with applicable electromagnetic interference standards. The power factor correction circuit converts AC power to a high DC voltage. For example, the high DC voltage can be 400 VDC. The DC to DC converter scales the high DC voltage down to a lower DC voltage as required by the load equipment to be powered by the power supply. 
     U.S. Pat. No. 5,949,671, issued to Lee on Sep. 7, 1999 and entitled “Power Supply With Re-Configurable Outputs For Different Output Voltages and Methods Of Operation Thereof” teaches a type of DC power supply that is well known in the prior art. The DC power supply taught by Lee has a pair of output rectifying circuits that are coupled in alternate configurations to provide dual voltages at an output of the DC power supply. The voltage supply taught by Lee is thus capable of providing different output voltages using a single voltage controller. 
     U.S. Pat. No. 4,626,981, issued to Su on Dec. 2, 1986 teaches a dual voltage converter circuit. The dual voltage converter circuit taught by Su converts an AC input voltage into an AC output voltage having a predetermined amplitude. The output voltage is coupled to a load circuit in order to energize the load circuit. When a relatively low amplitude AC mains supply voltage is applied to the converter the entire AC mains supply voltage is selectively coupled to a degaussing circuit without substantial amplitude change. On the other hand, when a relatively high amplitude AC mains supply voltage is provided a portion of the amplitude of the input AC mains supply voltage having an amplitude that approximates that of a lower AC mains supply voltages is coupled to the degaussing circuit. 
     Su also teaches coupling an AC input voltage to a rectifier arrangement of a voltage converter to develop DC voltages in a pair of capacitors. The rectifier arrangement combines the AC input voltage with the voltages in the first and second capacitors, respectively, to produce an output voltage. The output voltage energizes an AC utilization circuit such as a degaussing circuit. 
     During the positive portion of each cycle of the AC input voltage, the rectifier arrangement couples a positive difference voltage to the degaussing circuit. The positive difference voltage is formed between the positive portion of the AC input voltage and the voltage in the first capacitor to produce a positive level of the degaussing voltage. During the negative portion of each cycle of the AC input voltage, the rectifier couples a negative difference voltage to the degaussing circuit. The negative difference voltage is formed between the negative portion of the AC input voltage and the voltage in the second capacitor to produce a negative level of the degaussing voltage. 
     However, the power converters taught by Lee and Su are suitable only for resistive loads. They are not suitable for powering devices having electronic loads primarily because of voltage spikes and other signal distortions present in the output voltage signals of these converters. For example, a 120 volt rms signal at the output of a converter such as the one taught by Su may have peaks approaching those of a 240 volt signal. Such peaks can destroy electronic circuitry. 
     U.S. Pat. No. 4,314,327, issued to DePuy on Feb. 2, 1982, entitled “Transistor Drive Control For A Multiple Input DC To DC Converter” is an example of another type of prior art electrical energy conversion circuit. The conversion circuit taught by DePuy operates with major and minor variations in the level of applied input DC voltage and reduces the computational losses of its switching transistors that may other occur for the major and minor increases of the input DC voltage. 
     A base drive current circuit in the DuPuy converter includes a full wave rectifier and multiple level current limiting circuit which is interposed between a base drive winding of a saturable transformer and the base electrodes of the transistors of first and second transistor diode combinations. The base drive current circuit adapts the saturation condition of the first and second transistor diode combinations to the level of the applied DC input voltages. This reduces the level of increase of the computational losses of the transistor diode combinations. 
     Kruppa, in U.S. Pat. No. 5,805,439 issued on Sep. 8, 1998, teaches a DC to DC automatic switching circuit. The Kruppa device is a circuit for controlling multiple DC input voltages to produce a predetermined output voltage using a single DC to DC converter. Sensing of the DC input voltages supplied to the Kruppa switching device permits automatic switching in order to route an applied voltage between input terminals and output terminals. Furthermore, this switching permits configuring of a feedback network that selects the output voltage of the DC to DC converter. 
     U.S. Pat. No. 5,654,884, entitled “Multistand AC/DC Converter With Baseline Crossing Detection” issued to Mohan on Aug. 5, 1997 provides circuitry for use in an integrated circuit controlled voltage doubler/bridge circuit. This circuitry is adapted to detect a period during which there is a lack of AC supply voltage following a period of AC input voltage within a predetermined range of values. When this occurs repeated triac firing pulses are provided such that the AC supply is rectified and doubled as soon as the AC supply voltage returns. 
     Thus, it is known in the prior art to provide AC to AC converters which are not suitable for use with electronic devices. It is also known to provide converters which supply DC electrical energy suitable for use with electronic devices from an AC or a DC input. However, none of these devices are capable of providing AC/DC energy conversion suitable for use with electronic devices. It is known to solve these problems using a transformer. However, the use of a transformer increases the size, weight and cost of a power conversion device. 
     SUMMARY OF THE INVENTION 
     A method for performing power conversion in a power converter device provides a converter output AC waveform from a converter input AC waveform, the convertor input waveform having an input power level, an input frequency, an input waveform shape, and an input voltage/current characteristic. The converter input AC waveform is applied to a converter switch having a converter switch frequency and the switch is operated at the converter switch frequency to provide a switched waveform, the switched waveform having a plurality of switched waveform notches with a notch repetition rate substantially equal to the converter switch frequency. A filter performs filtering of the switched waveform to provide the converter output AC waveform having an output power level substantially equal to the input power level, an output frequency substantially equal to the input frequency, an output waveform shape substantially similar to the input wave form shape, and an output voltage/current characteristic substantially different from the input voltage/current characteristic. 
     The output voltage/current characteristic has an output voltage level substantially less than an input voltage level of the input voltage/current characteristic and an output current level substantially higher than an input current level of the input voltage/current characteristic. The converter input AC waveform has a positive half cycle and a negative half cycle and the switched waveform notches are formed during both the positive half cycle and the negative half cycle of the converter input AC waveform. The input waveform shape can be a sine wave and the output waveform shape can be a sine wave. Additionally, the input waveform shape can be a square wave and the output waveform shape can be a square wave. 
     The converter switch frequency is substantially higher than the input frequency and the filtering is performed by a filter having a filter a corner frequency that is at least twice as high as the input frequency. The converter switch frequency is substantially higher than the filter corner frequency. The filter has a frequency spectrum including a snitching component of the converter switch wherein the attenuation of the switching component by the filter is determined in accordance with the relationship: Attenuation in dB=12*log2(F sw 2F in ) and F sw  represents the converter switch frequency and 2Fin represents the filter corner frequency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram representation of the electronic power converter device of the present invention. 
     FIG. 2 is a graphical representation of an input waveform which can be applied to the input of the electronic power converter device of FIG.  1 . 
     FIG. 3 is a graphical representation of the operation of a switching circuit provided within the electronic power converter device of FIG.  1 . 
     FIG. 4 is a graphical representation of an output waveform that can appear at the output of the electronic power converter device of FIG.  1 . 
     FIG. 5 is a schematic representation of the circuitry of the electronic power converter device of FIG.  1 . 
     FIG. 6 is a more detailed schematic representation of the circuitry of the electronic power converter device of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, there is shown electronic power converter  10  of the present invention. During operation of electronic power converter  10 , an input AC waveform is applied to converter input port  12  which is defined by interconnect lines  18 ,  22 . An output AC waveform is provided at converter output port  26  of electronic power converter  10 . Converter output port  26  is defined by interconnect lines  20 ,  22 . Thus, interconnect line  22  is common to converter input port  12  and converter output port  26 . 
     The signal of common interconnect line  22  is applied to triacs/diodes block  24 . Input interconnect line  18  is also applied to triacs/diodes block  24 . Additionally, input interconnect line  18  is coupled to an output of waveform chopping switch  16  in order to permit power conversion of an input AC waveform applied to converter input port  12  in accordance with the method of the invention. 
     In order to perform conversion of an input AC waveform of converter input port  12  a plurality of triacs and diodes is provided within triacs/diodes block  24 . The triacs and diodes within triacs/diodes block  24  are adapted to switch into an off state under the control of waveform chopping switch  16  and to prevent signals from being applied to converter outport port  26  during portions of both the positive going cycles and the negative going cycles of the input AC waveform. This results in power conversion of an input AC signal while still providing an output signal having substantially the same frequency as the input which is suitable for application to a load device having electronic components therein. 
     Referring now to FIGS. 2,  3 ,  4 , there are shown input power waveform  40 , intermediate power waveform  50 , and converted output power waveform  60 , respectively. Each of the power waveforms  40 ,  50 ,  60  has a positive half cycle  42  and a negative half cycle  44 . The frequency, shape, power and phase of output power waveform  60  substantially follows those of input power waveform  40 , allowing for minor differences. The minor differences can be due to factors such as loss, noise and artifacts that may be introduced by electronic power converter  10 . 
     Input power waveform  40  is applied to converter input port  12  for conversion by electronic power converter  10  of the present invention. Intermediate power waveform  50  is then created within triacs/diodes block  24  of electronic power converter  10  in accordance with waveform chopping switch  16  as part of the power conversion process of the present invention. Converted output power waveform  60  is the output AC waveform of electronic power converter  10  which is provided at converter outport port  26 . 
     In order to convert input power waveform  40  into output power waveform  60 , a plurality of notches is formed in the input power waveform  40  during both the positive half cycles  42  and the negative half cycles  44  by the triacs and diodes of triacs/diodes block  24 . This results in the formation of waveform notches  52  and corresponding waveform peaks  54  shown in intermediate power waveform  50 . The manner in which the waveform notches  52  and waveform peaks  54  are formed by the triacs and diodes within triacs/diodes block  24  under the control of waveform chopping switch  16  as described in more detail below. 
     Waveform chopping switch  16  in the preferred embodiment of the invention is a two pole low pass switch. Using waveform chopping switch  16  the waveform notches  52  are formed when waveform chopping switch  16  is in a first switch position and the waveform peaks  54  are formed when waveform chopping switch  16  is in a second switch position. 
     Operation of waveform chopping switch  16  is controlled by switch control oscillator  14 . Switch control oscillator  14  can be adapted to have a switching frequency substantially higher than the frequency of input power waveform  40  in order to provide a suitable output power waveform  60 . For example, for a 60 Hz input power waveform  40 , the frequency of switch control oscillator  14  can be about 5 Kz. Intermediate power waveform  50  is filtered within electronic power converter  10  in order to provide the output power waveform  60 . 
     While input power waveform  40  is shown as a sine wave, it will be understood that the method of the present invention can be applied to input and output waveforms of any shape. For example, if input power waveform  40  is a square wave, a step function or any other sinusoid, the shape of output power waveform  60  is the same as the shape of input power waveform  40 , i.e. a square wave, a step function or other sinusoid, respectively. 
     Referring now to FIG. 5, there is shown a high level schematic representation of the electronic power converter  10  of the present invention. In the high level schematic representation of electronic power converter  10 , the input interconnect lines  22 ,  18 , defining the converter input port  12 , are coupled, respectively to switch terminals  16   a, b  of waveform chopping switch  16 . 
     When waveform chopping switch  16  is in a first switch position input interconnect line  18  and switch terminal  16   b  are electrically coupled to contact  16   c  of waveform chopping switch  16 . In this first position of chopping switch  16 , input power waveform  40  is applied to converter outport port  26  by way of filter inductor  66  which removes the sum and difference products caused by chopping switch  16  in cooperation with output capacitor  68 . The signal at the output of filter inductor  66  is coupled to converter outport port  26  by way of interconnect line  20 . This position of chopping switch  16  corresponds to the waveform peaks  54  of the intermediate power waveform  50 . 
     When waveform chopping switch  16  is in a second position, input interconnect line  22  of converter input port  12  is applied directly to filter inductor  66 . In this manner, the signal applied to output capacitor e by way of filter inductor  66  is substantially the same as the signal applied to the opposite end of output capacitor  68  by way of interconnect line  22 , thereby creating waveform notches  52  in intermediate power waveform  50 . 
     Thus, it will be understood that the series of repeating waveform notches  52  and waveform peaks  54  of intermediate power waveform  50  are provided within electronic power converter  10  of the present invention as waveform chopping switch  16  is repeatedly thrown from one position of the first and second positions to the other. Furthermore, it will be understood that the unused power of the power conversion process of the present invention is reflected back to the power source that provides input power waveform  40 . 
     The output filter formed by filter inductor  66  and output capacitor  68  can have a corner frequency of about 120 Hz depending on the permitted ripple of output power waveform  60  and the switching frequency of switch control oscillator  14 . The output filter of electronic power converter  10  must therefore be effective to remove the oscillator frequency and harmonics from output power waveform  60 . 
     Broadly, one of the purposes of the output filter is to reduce the switching component of the power spectrum of output power waveform  60  to an acceptable level. In order to perform this function, the output filter formed by filter inductor  66  and output capacitor  68  is preferably a two pole lowpass filter with a typical roll off characteristic of approximately −12 dB per octave at frequencies above the filter corner frequency. The relationship of the filter corner frequency of electronic power converter  10  is given by 1/(2*PI*SQRT(LC)) where L is the inductance of filter inductor  66  and C is the capacitance of output capacitor  68 . 
     If the corner frequency of the output filter is chosen to be sufficiently above the input frequency of input power waveform  40  there is negligible power loss in electronic power converter  10 . Such substantially low power loss is necessary to provide substantially the same power for power waveforms  40 ,  60 . In order to meet this specification a good approximation of the output corner frequency can be to limit it to a value higher than an octave above the highest harmonic of interest in input power waveform  40 . 
     The relationship of the switching frequency of waveform chopping switch  16  to the frequency of input power waveform  40  should be one in which the switching frequency is sufficiently higher than the frequency of input power waveform  40  so as to provide sufficient attenuation of the switching component in the spectrum by the output filter while not providing substantial attenuation of input power waveform  40 . It the input frequency, F in , is a sinusoid and the corner frequency of the output filter is chosen to be 2F in , the relationship between the switching frequency and the amount of attenuation of switching component in the spectrum of the output signal is as follows: Attenuation in dB=12*log2(F sw /2F in ), where F sw  is the switching frequency and 2F in  is twice the corner frequency of the output filter. 
     Intermediate power waveform  50 , formed in this manner, appears at the input of waveform chopping switch  16 . Intermediate power waveform  50  appears between chopping switch  16  and filter inductor  66 . Output power waveform  60  appears at the output of filter inductor  66 . It will be understood by those skilled in the art that electronic power converter  10  thus performs the AC/AC power conversion of the present invention independently of any AC/DC conversion and independently of any DC/DC or DC/AC power conversions. 
     Referring now to FIG. 6, there is shown a more detailed schematic representation of power converter device  10  of the present invention, including a more detailed representation of switch control oscillator  14 . Switch control oscillator  14  can be a conventional feedback operational amplifier oscillator circuit  70 . As previously described the oscillation frequency of feedback operational amplifier circuit  70  should be substantially higher than the frequency of input power waveform  40 . 
     The output of operational amplifier oscillator  70  is driven by drive transistors  72  and drive MOSFET  73  prior to being applied to waveform chopping switch  16  in order to permit operational amplifier oscillator circuit  70  to control the switching of chopping switch  16 . It will be understood that chopping switch  16  in the preferred embodiment of the invention may be energized by a DC voltage, although no DC conversion is involved in performing its operations. In this manner input power waveform  40  and the oscillator frequency of oscillator circuit  70  are multiplied by each other. It will be understood by those skilled in the art that chopping switch  16  can be triggered at any phase within the input power waveform  40  since the triggering of chopping switch  16  is not synchronized with any line voltage or any other reference signal. 
     In the preferred embodiment of the invention, the duty cycle of the output signal of oscillator circuit  70  can be approximately fifty percent. However, it will be understood by those skilled in the art that the duty cycle of the output signals of oscillator circuit  70  is determined by the power division factor required between input power waveform  40  and output power waveform  60 . 
     Output terminal  80   a  of waveform chopping switch  16  is applied to the gates of two triacs  76   a,b  within triacs/diodes block  24  byway of respective diodes  74   a,b . Diodes  74   a,b  are coupled to output terminal  80   a  of chopping switch  16  with opposite pluralities. Thus, during one-half cycle of input power waveform  40  the gate of triac  76   a  is triggered by diode  74   a  and during the other half-cycle triac  76   a  is in a conducting state. 
     In this manner the input of filter inductor  66  is alternately connected to either input interconnect line  18  or input interconnect line  22  of converter input port  12  to alternately form the waveform notches  52  and the waveform peaks  54  of intermediate power waveform  50  as previously described. The signals of triacs  76   a,b  are applied to filter inductor  66  by way of clamping diodes  78   a,b . Clamping diodes  78   a,b  provide return current paths for filter inductor  66  when triacs  76   a,b  are alternately conducting. 
     Thus, the frequency, the waveform shape and the power of output power waveform  60  are substantially the same as the frequency, the waveform shape, and the power of input power waveform  40  while, simultaneously, the voltage/current characteristics of power waveforms  40 ,  60  can differ substantially. The differences in voltage/current characteristics between power waveforms  40 ,  60  can be controlled in accordance with the duty cycle of switch control oscillator  14  and, thereby, the duty cycle of waveform notches  52  and waveform peaks  54  within intermediate power waveform  50 . 
     An example of such a power conversion wherein voltage and current are converted but the frequency, waveform shape, and power are not converted can be as follows. The voltage/current characteristics of input power waveform  40  can be, for example, 100 watts input at 100 volts and 1 amp. The 100 watt input power waveform  40  can be converted into an output power waveform  60  of approximately 100 watts at 50 volts and 2 amps. Thus, the conversion performed by electronic power converter  10  is in accordance with Watt&#39;s Law, wherein the decrease in voltage level is accompanied by a corresponding proportional increase in the current level. The conversion of power without conversion of frequency, waveform shape or power is similar to the conversion performed by a conventional step down transformer or by an impedance transformation. 
     Without further elaboration, the foregoing will so fully illustrate my invention that others may, by applying current or future knowledge adopt the same for use under various conditions of service.