Voltage Waveform Synthesizer and a System That Includes the Same

The present invention relates to systems wherein an ac waveform is synthesized from dc or unidirectional sources of electric enery.

There accompanies herewith an application for Letters Patent entitled "Electronic Motor that Includes an Electronic Waveform Synthesizer and the Synthesizer Per Se" Ser. No. 686,355 filed May 14, 1976, now U.S. Pat. No. 4,060,754 (Kirtley et al). Attention is called also to the following U.S. Letters Pat. No. 3,748,492 (Baker); 3,866,060 (Bannister et al); 3,867,643 (Baker et al); 3,899,689 (Baker); 3,909,685 (Baker et al); 3,942,028 (Baker); 3,983,503, (Bannister et al); 3,971,976 (Baker); and 4,039,909.

The synthesis of ac waveforms by combining a plurality of dc or unidirectional sources requires not only that the technical requirements be fulfilled but that the economic constraints be met, as well. It is an object of the present invention to provide a waveform synthesizer that satisfies both requirements.

While the synthesizer herein disclosed may be used to power single-frequency loads with a constant or a variable voltage amplitude, it is capable, as well, of varying the frequency over a wide range from zero to some maximum value. Often, when such variation is effected, harmonics become a problem; the present inventor has found, however, that the harmonics content of the synthesized waveform can be controlled, irrespective of the output voltage and/or frequency required. A further object of the invention, therefore, is to provide a synthesizer in which the harmonic content in the output waveform is controllable, independent of output voltage and frequency.

Another object is to provide a waveform synthesizer that can monitor the interchange of electric energy in the system of which the synthesizer is a part.

The waveform synthesizer is hereinafter discussed in a system that includes a rotating electric machine which may be an electric motor or an electric generator or a machine that performs both functions. In any event, it is often necessary to control interchange of electric energy between the synthesizer and the machine such that the synthesizer accepts as well as delivers electric energy and to modulate the level of energy interchange. By way of illustration, in the case of a variable-speed electric motor, it is well known that where motor speed is varied over a wide range (say from zero to some maximum) it is advantageous to control the electric power input to the motor; in said patents, the proposal is made to change the voltage applied to the motor terminals to accomplish this end. The present inventor has found, however, that such complete power control in terms of controlling the voltage, frequency and harmonic distortion independently can be effected by changing the widths of the steps forming the synthesized waveform and in an almost infinite set of increments from zero to the maximum requirement. It is, therefore, a still further object to provide an electronic machine having novel speed capabilities and other characteristics.

Still another object is to provide a novel solid state phase shifter.

A further object is to provide a solid state waveform synthesizer that employs thyristors in an unusual arrangement and wherein there is shown a novel low voltage scheme to back bias the thyristors and thereby turn off the same.

These and still further objects are addressed hereinafter.

The foregoing objects are achieved, in part, in an electronic waveform synthesizer which includes a plurality of units each of which comprises one or more stages, each said stage comprising dc or unidirectional supply voltage means and stage switch means. The waveform synthesizer further includes electronic mixer switch means and control logic means. The foregoing elements interact to provide an alternating waveform in the form of steps formed under the direction of the control logic means. The widths of the steps are controllable to affect the power transfer in the synthesized wave as well as to affect the harmonic content therein; also, in some cases, each half-wave of a cycle of the synthesized waveform is formed by a plurality of pulses whose widths are much less than the half-wave and whose widths and spacings of timings are established by the control logic means; this configuration gives independent control of the voltage amplitude and frequency to give any desired voltage waveshape. Thus, an acceptable level of harmonic content can be obtained in the synthesized waveform. A very favorable form of electronic mixer switch means is shown comprising thyristors with a novel way to back bias the thyristors. The synthesizer disclosed herein has a wide practical use; it is shown herein, however, in the context of an electronic motor which is one such use, and an important one.

The invention is hereinafter described with reference to the accompanying drawing in which:

FIG. 1 shows schematically, and partly in block diagram form, an electronic waveform synthesizer that combines dc or unidirectional voltages to form a single phase, ac output in the form of a quasi-sinusoid;

FIG. 2A is a schematic representation, partly block diagram in form, of a synthesizer similar to that shown in FIG. 1;

FIG. 2B shows an ac, time-voltage waveform synthesized by the circuit of FIG. 2A;

FIGS. 3A-3G show further time-voltage waveforms that can be synthesized by the circuit of FIG. 2A;

FIG. 4A is a schematic representation, partly block diagram in form of half of the circuit of FIG. 2A, plus some other circuit elements;

FIG. 4B shows an ac, time-voltage waveform synthesized by the circuit of FIG. 4A;

FIG 5A is a schematic of some of the circuit of FIG. 4A;

FIG. 5B is a dc, time-voltage waveform synthesized as a number of pulses by the circuit of FIG. 5A;

FIG. 5C-5K are ac, time-voltage waveforms synthesized by the circuit of FIG. 5A;

FIG. 6 is a schematic representation, partly block diagram in form, of digital logic to control the synthesizers herein;

FIG. 7 is a schematic representation, partly block diagram in form, of a three-phase synthesizer that powers a three-phase rotating machine;

FIG. 8 is a schematic representation, partly block diagram in form, showing a plurality of electronic waveform synthesizers powering a rotating electric machine having a multi-coil closed loop winding;

FIG. 9A is a schematic representation, partly block diagram in form, of a system wherein the output of a single-phase source of electric energy is processed to provide a polyphase electric energy which is connected to a rotating electric machine, one coil of the winding of the two-phase machine shown being connected directly across the line of the incoming single-phase source and the other coil thereof being connected through a phase-shifter;

FIG. 9B is an ac, time-voltage diagram of the output of the phase-shifter portion of the system of FIG. 9A;

FIG. 10 is a schematic representation, partly block diagram in form, of a modification of the phase-shifter portion of the system of FIG. 9A;

FIG. 11 is a schematic representation, partly block diagram in form of a modification of the system of FIG. 1; and

FIG. 12 is a voltage-time diagram to aid in the explanation of the operation of the digital logic circuits of FIG. 6.

The present invention is multifaceted: it is directed to a novel way of mixing dc or unidirectional voltages in an unusually beneficial way to synthesize an alternating (ac) waveform; it is directed to processing the dc or unidirectional voltages in a new and unusual manner to achieve acceptable harmonic levels in the synthesized waveform as well as to regulate electric power flow; and it employs, in an important aspect thereof, a mixing arrangement wherein thyristors are employed and there is disclosed an extraordinary way of reverse biasing the thyristors so they turn off automatically. The last mentioned aspect of the invention, that which relates to thyristors, is particularly important for systems wherein electrical power transfer is in the kilowatt range (i.e., power-type loads) and with voltage requirements above, say, about two hundred volts, since the combination of high current and high voltage, in the economic constraints of the market place, render synthesizers often prohibitively expensive when the output power is channeled through power transistors. Relatively low priced thyristors, on the other hand, can process electric energy at high voltage and high current, but such low priced thyristors are very difficult to turn off. One very important aspect of the present invention is the novel way invented to effect such turn-off. An important use for a synthesizer with the characteristics described in this paragraph is that of variable speed, polyphase, ac motors and the like and the invention is placed in the context of such machinery. In the explanation that now follows, the invention is taken up, in its various aspects, somewhat in the order just given; an attempt is made to use the same or similar labels for those elements that perform the same or similar functions in the various figures.

Turning now to FIG. 1, an electronic waveform synthesizer is shown at 101A having, in combination, a first or positive unit 98A and a second or negative unit 99A comprising Stage 1.sub.A . . . Stage N.sub.A and Stage 1.sub.B . . . Stage N.sub.B, respectively. The synthesized output waveform of the unit 98A is a positive-going waveform 80.sub.A and the synthesized output waveform of the unit 99A is a negative-going waveform 80.sub.B that are connected by conductors 50.sub.A and 50.sub.B, respectively, to an electronic mixer 20.sub.A which combines the same, in a manner later described herein, to provide an ac waveform 81 that is successively the output of the first unit 98A, then the output of the second unit 99A, then the output of the first unit 98A, and so forth. The network 101A includes control logic 30.sub.A (which is preferably digital but which may be analog) that programs the events in the two units 98A and 99A and in the electronic mixer 20.sub.A to give the results desired.

The first unit 98A comprises Stage 1.sub.A that includes dc or unidirectional supply voltage means (i.e., the battery labeled B.sub.A which is usually rechargeable and supplies E volts herein) and bilateral stage switch means S.sub.1-1A and S.sub.2-1A each of which is shown to be a transistor and diode in back-to-back connection, as described in great detail in said patents. The stage switches S.sub.1-1A and S.sub.2-1A serve to control electric current flow in the battery B.sub.A as well as to effect electrical bypass of the battery B.sub.A. The unit 98A is an N-stage system (where N.gtoreq.1) of which two stages are shown, the Nth stage, Stage N.sub.A, comprising dc or unidirectional supply voltage means (i.e., the capacitor labeled C.sub.1-NA in the Stage N.sub.A) and bilateral solid state switches S.sub.1-NA and S.sub.2-NA that perform similarly to the switches S.sub.1-1A and S.sub.2-1A.

The corresponding elements in the unit 99A are Stage 1.sub.B . . . Stage N.sub.B, as above indicated, that respectively include energy storage means B.sub.B . . . C.sub.1-NB, first bilateral stage switches S.sub.1-1B . . . S.sub.1-NB and second bilateral stage switches S.sub.2-1B . . . S.sub.2-NB.

A few further matters, some of a general nature, with regard to the embodiment of FIG. 1 are contained in this paragraph. It is shown in later figures that the batteries B.sub.A and B.sub.B (each of which supplies E volts herein) can be capacitors energized by a battery or other primary source of electric energy; on the other hand, the Nth Stage, or any intermediate stage can have a battery as its supply voltage means -- or the stage supply voltage means can be a fuel cell, or a solar cell or the like. In the embodiment of FIG. 1, the capacitor C.sub.1-NA is charged by the battery B.sub.A through a zener diode D.sub.3-1 ; any further intermediate stages would have diodes between stages, but zener diodes need not necessarily be used.

The semiconductors that form the switches S.sub.1-1A and S.sub.2-1A alone are marked: the are respectively Q.sub.1-1 -D.sub.1-1 and Q.sub.2-1 -D.sub.2-1. The waveform 81, that appears at output M of the electronic mixer 20, is a two-step waveform (as are, also, the waveforms 80.sub.A and 80.sub.B) that consists of a first step 81.sub.A (also called step 1 or window 1 herein) and a step 81.sub.B (also called step 2 or window 2 herein) of the positive half cycle of the waveform 81 and corresponding steps 81.sub.A ' and 81.sub.B ' of the negative half. It is later shown that the power carried by the wave 81 is varied from zero to some maximum by varying the width of the steps 81.sub.A, 81.sub.B, 81.sub.A ' and 81.sub.B '. It is pointed out that the harmonic content of the waveform 81 is also affected by varying the step width. In addition, the individual steps, e.g., 81.sub.A and 81.sub.B, that make up each half cycle of the waveform 81, can comprise a plurality of pulses and either the pulse width or pulse timing, or both, can be regulated by the control logic means to establish an acceptable level of harmonic content in the waveform 81, but that aspect of the invention is left to later paragraphs. What follows now is an explanation with reference to FIGS. 2A and 2B of the operation of a preferred form of the electronic mixer which takes as input the positive-going wave 80.sub.A and the negative-going wave 80.sub.B and produces therefrom at the terminal M the ac waveform 81.

The electronic waveform synthesizer labeled 101B in FIG. 2A is similar to the synthesizer 101A and is shown mostly to shown details of the mixer labeled 20.sub.B and a scheme for controlling the thyristors therein. It will be appreciated that the schematic switches shown at S.sub.1A . . . S.sub.NA and S.sub.1B . . . S.sub.NB correspond to the transistors Q.sub.1-1, Q.sub.2-1, etc., but other type switching mechanisms can be used. The switches S.sub.1A, etc., are semiconductor switches and are bilateral as discussed in said patents. The electronic mixer 20.sub.B is shown in FIG. 2A comprising thyristors SCR.sub.1A and SCR.sub.1B connected in parallel with reverse polarity diodes D.sub.1-A and D.sub.1-B, respectively; the thyristors and diodes so connected form bilateral mixer switches. To simplify the explanations, a number of terms should be defined. An "active" thyristor device is one that has a gate voltage such that it will conduct when forward biased, that is, an active thyristor will conduct when a forward bias voltage occurs across the device and will cease to conduct when back biased and the current passes through zero. When a thyristor is switched from active to inactive while conducting, it will continue to conduct until the current goes through zero; it will then remain nonconducting. If switched to inactive while nonconducting, the device will remain nonconducting even with a forward bias voltage applied. Inactive devices remain nonconducting regardless of the voltage bias. When an inactive device is switched to active, it conducts on first appearance of forward bias voltage and then operates as described for an active device. The thyristors are rendered active by applying appropriate signals to the gates of each, and they are rendered inactive by removing the gate signal. The gate signals are generated by the control logic and are connected to the thyristors by a conductor or conductors 15'.

The synthesizer 101B can provide a synthesized waveform like the waveform 81 in FIGS. 1, 2B and 3 to a load; that waveform is provided by appropirate switching of the switches S.sub.1A . . . and switching of the thyristors SCR.sub.1A and SCR.sub.1B in a sequence, as now discussed with reference to FIGS. 2A and 2B. The triggering of the thyristors SCR.sub.1A and SCR.sub.1B is synchronized by control logic 30.sub.B with operation of the switches S.sub.1A, S.sub.NA, S.sub.1B and S.sub.NB (to simplify the explanation, it is assumed here that the synthesizers are two-stage per unit devices, even though there may be N stages per unit, and it is hereinafter shown that with a modified mixer N can equal one). The thyristor SCR.sub.1A is rendered active at time .DELTA.T.sub.o in FIG. 2B and is rendered inactive at .DELTA.t.sub.4 ; in addition the thyristor SCR.sub.1A is back biased, in a way later described, at time .DELTA.t.sub.4. The thyristor SCR.sub.1B is rendered active at time .DELTA.t.sub.5 and inactive and back biased at time .DELTA.t.sub.9. In this way the positive-going portion and the negative-going portions, respectively, of the waveform are generated. The steps (or windows) 81A and 81B (and the corresponding steps of the negative-going portion of the wave 81) are generated by the switches S.sub.1N and S.sub.1A, respectively. To generate the step (or window) 81.sub.A, the switch S.sub.NA is in the up ("U") position in FIG. 2A and the switch S.sub.1A is in the down ("D") position. To generate the step 81.sub.B the switch S.sub.1A is moved to the up position so that between times .DELTA.t.sub.2 and .DELTA.t.sub.3 in FIG. 2B the switches S.sub.1A and S.sub.NA are both up. During the occurrence of the positive-going half of the waveform 81, the switches S.sub.1B and S.sub.NB are up. At time .DELTA.t.sub.3 the switch S.sub.1A is switched down and at time .DELTA.t.sub.4 and the switch S.sub.NA is switched down. At time .DELTA.t.sub.5 the switches S.sub.1A and S.sub.NA are both down; at time .DELTA.t.sub.6 the switch S.sub.NB is switched down, the switch S.sub.1B being down; between times .DELTA.t.sub.7 and .DELTA.t.sub.8 both the switch S.sub.NB and the switch S.sub.1B are down. During the negative-going half of the waveform 81, the switches S.sub.1A and S.sub.NA are down. There now follows a discussion of how the thyristors SCR.sub.1A and SCR.sub.1B are rendered nonconducting, and, in this connection, the batteries B.sub.1 and B.sub.2 in FIG. 2A play a vital part; the batteries B.sub.1 and B.sub.2 are low voltage (.DELTA.V), say about five percent the potential E of either of the batteries B.sub.A and B.sub.B.

During the time intervals between .DELTA.t.sub.9 and .DELTA.t.sub.0 ' in FIG. 2B and between the times .DELTA.t.sub.4 and .DELTA.t.sub.6, the switches S.sub.NA and S.sub.1A are both down and the switches S.sub.NB and S.sub.1B are both up. Therefore, during these time intervals, the output of the positive unit 98B is connected to -.DELTA.V and the output of the negative unit 99B is connected to +.DELTA.V. Because of this, a voltage of 2 .DELTA.V exists across the diodes D.sub.1-A and D.sub.1-B so that the thyristors SCR.sub.1A and SCR.sub.1B are both reversed biased and are turned off at the times .DELTA.t.sub.4 and .DELTA.t.sub.9. The thyristor SCR.sub.1A is activated at the time .DELTA.t.sub.0 and de-activated at .DELTA.t.sub.4 ; the thyristor SCR.sub.1B is activated at the time .DELTA.t.sub.5 and de-activated at the time .DELTA.t.sub.9.

The batteries B.sub.1 and B.sub.2 in concert constitute a source of positive and negative electric potential, points 18.sub.B and 19.sub.B, respectively, in FIG. 2A, connected in an electrical bridge configuration respectively through the bilateral switches S.sub.1A . . . S.sub.NA of the first unit 98B and the bilateral switches S.sub.1B . . . S.sub.NB of the second unit 99B to the anode of the thyristor SCR.sub.1A and the cathode of the thyristor SCR.sub.1B. The thyristors SCR.sub.1A and SCR.sub.1B are serially connected and the serial connection labeled 17.sub.B serves as a port of the synthesizer 101B, the other port being ground G, as shown, the connection 27.sub.B being brought out to the terminal or output M. (Later in FIGS. 9A and 10 the mixer means is shown comprising two pairs of serially connected thyristors wherein the load is connected between the serial connection between the thyristor pairs; the anode of one thyristor of one serial pair is connected to the anode of one thyristor of the other serial pair and back through the stage switches of the positive unit to the negative potential point, and the cathode of one thyristor of one serial pair is connected to the cathode of one thyristor of the other serial pair and back through the stage switches of the negative unit to the positive potential point.) The network configuration just described provides a low voltage means for applying the reverse-bias voltage .DELTA.V to the thyristors at an appropriate time in the synthesizing cycle. Appropriate gating signals to the thyristors are applied by the control logic.

Waveform management is a unique feature of switched source synthesizers (e.g., the synthesizers 101A and 101B). Consider the stepped waveform shown in FIG. 3E where again the waveform is marked 81. The amplitude of the rms voltage of the equivalent sinusoid can be made larger by increasing the widths of the step 1 and the step 2 (increasing .delta..sub.1 and .delta..sub.2, respectively). This is shown in FIGS. 3F and 3G. Similarly, the rms voltage can be made smaller by decreasing the width of the steps (decreasing .delta..sub.1 and .delta..sub.2) as shown in FIGS. 3D, 3C, 3B, and 3A. Therefore, control of the synthesized output waveform is accomplished by simply varying the times at which switches S.sub.NA and S.sub.1A of FIG. 2 are flipped up and back down for the positive steps, and the times when switches S.sub.NB and S.sub.1B are switched for the negative steps. In fact, not only is the amplitude of the rms voltage controlled by the switch activation pattern, but also the harmonic content and frequency of the output waveform as well. The overall logic system for controlling the switch pattern in shown in FIG. 6 and discussed later, but before that a brief explanation of this very important waveform control is given next with reference to FIG. 4A which shows a single positive-going unit comprising stages like the units 98A and 98B, respectively, in FIG. 1 and to FIG. 4B which shows a waveform synthesized by the circuitry of FIG. 4A. Referring to FIG. 4A, in order to generate the positive portion of the stepped waveform in FIG. 4B, switches S.sub.NA and S.sub.1A must be switched at predetermined intervals. To generate window 1 (+) for the example waveform shown in FIG. 4B, the switch S.sub.NA is switched up at 15.5.degree. (electrical degrees) and back down at 164.5.degree.. Control of the switching intervals is accomplished by first dividing the quasi-sinusoid in FIG. 4B into 512 equal time intervals (256 parts for one-half of the sinusoid) and then setting a particular digital number (corresponding to the switching interval desired) into a presettable up/down counter 5.sub.N of control logic 30. For the example waveform in FIG. 4B, the digital number 234 is set into the counter 5.sub.N at time t.sub.0 (zero degrees). The counter 5.sub.N counts up to 256, it recycles through zero, and then it counts back up, reaching the number 105 at the 90.degree. point in the waveform cycle. At the 90.degree. point, the counter 5.sub.N is "reversed" and counts back down from 105 through zero to 256 and reaches 234 again at exactly the 180.degree. in the cycle. At the two zero point in the count, pulses from the counter trigger operation of the switches in the synthesizer; more precisely, at the first zero point (i.e., 15.5 electrical degrees) the switch S.sub.NA is switched up and at the second zero point (i.e., 164.5 electrical degrees) the switch S.sub.1A is switched down. Said another way, because the number 234 was originally set into the counter 5.sub.N and it was allowed to start counting up at time = t.sub.0 (0.degree.), it makes the transition from 256 .fwdarw. 000 at the 15.5.degree. point in the cycle and from 000 .fwdarw. 256 at the 164.5.degree. (180.degree.-15.5.degree.) point in the cycle. This is a unique feature of the present method of generating window widths; the up/down counter sequence always gives, automatically, the timing symmetry required to generate a symmetrical waveform. Moreover, the window size (waveform shape) can be changed by merely setting a different number into the counter at the beginning of any particular cycle.

The width of window 2 in FIG. 4B is controlled in the same manner; the digital number 192 is set into a second up/down counter 5.sub.1 at the beginning of the cycle (at time t.sub.0). The counter is allowed to count up, reaching the count 256 .fwdarw. 000 at 45.degree. and the count 64 at 90.degree. at which juncture the counter 5.sub.1 is reversed; it then counts down from 64, reaching 000 .fwdarw. 256 at 135.degree. and the count 192 again at 180.degree..

In the above discussion regarding control of the window widths, it is interesting to note that both of the counters 5.sub.N and 5.sub.1 count up, reverse direction and then count back down to reach the same number at the 180.degree. point in the cycle that was originally transferred into the counter at the 0.degree. point (i.e., the start of the cycle). This fact is important because it allows the counter 5.sub.N and 5.sub.1 to function in the same manner and repeat the same action to control the window widths for the negative section (that is, to control the switches S.sub.NB and S.sub.1B of FIG. 2A) to generate the negative portion (i.e., window 1(-) and window 2 (-)) of the stepped waveform.

Again, the discussion with reference to FIGS. 4A and 4B relate to a two-stage unit to produce a two-step or two-window synthesized waveform, but it applies to an N-stage system to provide an N-step or N-window waveform. In the system of FIG. 4A the battery B.sub.A again supplies E volts. The output of the counters 5.sub.N . . . 5.sub.1 are amplified by amplifiers 6.sub.N . . . 6.sub.1, respectively. The input numbers (i.e., the counts 234 and 192 in the above example) are introduced to the counters by analog-to-digital converters 7.sub.N . . . 7.sub.1 (or some other means known to workers in this art). Circuitry to effect switching of switches S.sub.NA and S.sub.1A is disclosed in one or more of the above-mentioned patents and need not be repeated here; workers in the art to which this invention pertains can interconnect the counters 5.sub.N . . . 5.sub.1 in the system with no difficulty.

The method described above to control the window width is an important concept because by the simple expediency of transferring two digital numbers at the beginning of the cycle of a waveform, (1) both of the amplitude (i.e., the rms voltage) and harmonic content of the waveform can be altered, (2) waveform symmetry is obtained automatically with a few standard low cost digital circuit chips, and (3) the control system is logically self-consistent, that is, it is locked to the system clock and can work (generate) at any frequency from dc to several thousand Hertz.

It will be appreciated on the basis of the foregoing explanation, that a polyphase system can be controlled in a similar fashion and with appropriate timing of the phases. The use of digital timing not only has the advantage of economics, it has also the advantage that the various events so controlled can be interlocked to one another quite easily to assure proper sequence; that facts holds true for a polyphase system.

As above stated, harmonic distortion in the synthesized waveform can be modified by changing the widths of the steps that compose the waveform. It should be further noted that the harmonic distortion can also be modified by forming one or more of the steps of the waveform as a plurality of pulses whose pulse width and/or pulse timing are controlled to affect said harmonic distortion, as now explained with reference to FIGS. 5A-5K.

It will quickly be observed that the two-stages of FIG. 5A are identical to the stages in FIG. 4A and that the waveforms of FIGS. 5G and 5H are similar to the waveform of FIG. 4B except for the widths of the step 1 and step 2. The waveform of FIG. 5F is a single step which is equivalent to step 1. The waveform in FIG. 5B is a dc waveform made up of a plurality of pulses; the waveforms of FIGS. 5C, 5D and 5E comprise a single step also made up of a plurality of pulses. The difference between the waveforms of FIGS. 5B, 5C, 5D and 5E is that the waveforms in each figure have a different spacing of pulses for every other figure giving a different average value. FIGS. 5C, 5D and 5E show a single step waveform, FIGS. 5I, 5J and 5K show two-step waveforms wherein the steps are formed by a plurality of pulses. The pulses that form the single step waveform of FIG. 5C, for example, or the two-step waveform of FIG. 5K can be generated by sequencing the switches S.sub.NA and S.sub.1A, as before. The advantage of generating waveforms like the waveform in FIG. 5K, for example, is that the amplitude, the frequency and the harmonic content of the synthesized quasisinusoid can be controlled mostly independently.

There follows now an explanation of the digital control logic which is shown in detail in FIG. 6.

The control logic labeled 30' in FIG. 6 differs somewhat from the control logic 30 of FIG. 4A. It should be noted, however, that the presettable counters 5.sub.N and 5.sub.1 and the amplifiers 6.sub.N and 6.sub.1 can be the same as the similarly marked elements of FIG. 4A. For purposes of this explanation let it be assumed that the control logic 30' is employed to perform the functions required of the control logic 30.sub.B in FIG. 2A to provide the waveform 81 in FIG. 2B. In this explanation the arrows labeled W.sub.1A and W.sub.2A represent electrical connections to the switches S.sub.NA and S.sub.1A, respectively, in the unit 98B to provide, respectively, the first window or step 81.sub.A in FIG. 2B and the second window or step 81.sub.B therein; the arrows labeled W.sub.2A and W.sub.2B represent electrical connections to the switches S.sub.NB and S.sub.1B, respectively, to provide the corresponding windows or steps in the negative half of the waveform 81 in FIG. 2B. The conductor labeled 15 in both figures represents one or more connections from the control logic to the electric mixer 20.sub.B and, more specifically, to the gates of the thyristor SCR.sub.1A and SCR.sub.1B to introduce reference signals at frequency f.sub.0 for polarity inversion, that is, the signals at the frequency f.sub.0 time and activate the thyristors to effect the appropriate switching thereof and by this way provide the positive half cycle of the waveform 81 and a negative half cycle thereof. In a system controlled by the logic 30', the outputs W.sub.1B and W.sub.2B are controlled by signals from the counters 5.sub.N and 5.sub.1 that have been inverted by inverters 8.sub.N 8.sub.1, respectively.

The waveform 81 in FIG. 2B can be thought of as being divided into a large number of equal time intervals (in the explanation here, 512 parts, i.e., the count for a complete cycle is 512; the explanation here is somewhat repetitious of the previous explanation with reference to FIGS. 4A and 4B). The window counters 5.sub.N and 5.sub.1 of FIG. 6 are modulus 8 and therefore require 256 clock pulses to recycle. In addition, the counters 5.sub.N and 5.sub.1 are presettable up/down counting units which can be arranged to output a pulse whenever the counter passes through its minimum count. FIG. 12 illustrates the operation of these counters. Let it be assumed that it is desired to introduce the voltage source C.sub.1-NA of the series combination 98B in FIG. 2A 12 electrical degrees after .DELTA.t.sub.0 ; this is done by triggering the switch S.sub.NA by a carry pulse from the counter 5.sub.N, as previously noted, as indicated in FIG. 12 and to remove the same source at 168.degree., i.e., the source C.sub.1-NA is to be added or introduced into the system and subtracted symmetrically. From the formulas of FIG. 12, the desired program number is:

Circuit operation is as follows: The counter 5.sub.N starts counting up from its program number 239 at time .DELTA.t.sub.0 in FIG. 2B. Seventeen clock pulses later, or approximately 12.degree. from the origin, the counter reaches its maximum count and outputs a carry pulse at the beginning of the next clock period. Counting in the up mode is allowed to continue until the peak V.sub.p or 90.degree. point of the sine wave in FIG. 12 is reached. At this point the digital number in the counter 5.sub.N is 111. The down count will then start at this point from digital number 111 and at 168.degree. from the origin, or 12.degree. from the 180.degree., the counter 5.sub.N will output another carry pulse. Counting down will continue to the 180.degree. point at which point the counter 5.sub.N is back to its original state. This technique of counting up and then down produces symmetrical spaced timing or carry pulses and, hence, a guaranteed symmetrical sinusoid. It should be noted that the times at which the voltage sources C.sub.1-NA, etc., are added and subtracted varies directly with the program number that is programmed into the counter at .DELTA.t.sub.0.

The window programmer shown at 7 in FIG. 6, based on the values of the feedback and reference voltages, varies the digital number in the window counters 5.sub.N and 5.sub.1 at time .DELTA.t.sub.0 in a direction such that the output voltage of the synthesizer 101B is maintained under various loading conditions and voltage levels of the source. The up/down counter labeled 13 within the window programmer 7 of FIG. 6 receives a fixed clock up rate from a phase locked loop (PLL) 12 (through a counter 11) and a variable clock-down rate from a VCO 14 whose control from a voltage amplifier 16 is the difference between feedback voltage V.sub.f.b. and some reference voltage V.sub.REF. If the clock-up and clock-down rates are equal, i.e., there is no "error voltage", the digital number in the up/down counter 13 remains constant (within the least significant bit), and the number in the window counters 5.sub.N and 5.sub.1 at time .DELTA.t.sub.0, therefore, remains unchanged.

Let it be assumed now that the output voltage of the synthesizer 101B increases due to some disturbance on the system such as, for example, a sudden reduction in the load. The input voltage to the VCO 14 will then increase which, in turn, increases the clock-down rate. Because clock-up rate is constant, the counter 13 will now be counting down faster than it is counting up and, hence, the digital number in the counter 13 will decrease. This decreased digital number is transferred to the window counters 5.sub.N and 5.sub.1 at the time of the zerocrossing of the quasi-sinuosid 81, and the output voltage of the system will decrease. The feedback voltage V.sub.f.b. will then decrease, which, due to the feedback connection, decreases the clock-down rate; and a new steady state at a reduced voltage will be reached.

The control logic 30' acts to generate window 2(+) and window 2(-) in FIG. 2B directly; that is, signals at W.sub.2A and W.sub.2B are direct signals from the logic 30', whereas, window 1(+) and window 1(-) are derived and determined by the magnitude of window 2 in each case. More precisely, the up/down counter 13 of the window programmer 7 provides a digital number x to the counter 5.sub.1 ; the digital number x is also simultaneously introduced as one input to an adder 17 to which is supplied, as further input, a fixed displacement y to generate the window 1(+) and the window 1(-) at some fixed time from the window 2(+) and the window 2(-), respectively. Due to the asynchronous nature of the clock-down rate in the programmer 7, the clock-up rate to the up/down counter 13 is synchronized by a synchronizing signal from the combination of the phase locked loop 12 and the .div. 12 counter 11, as shown. The signal V.sub.f.b. can be derived from the point M in FIG. 2A; the signals V.sub.REF, V.sub.offset and V.sub.0 are biasing voltages that are established at appropriate levels, as is known to workers in the art to which the specification is directed.

The system labeled 102 in FIG. 7 is a rotating electronic machine that consists of a three phase electronic synthesizer 101C and a rotating electric machine 40A. It will be appreciated, upon close inspection, that the synthesizer 101C essentially comprises three synthesizers like the synthesizer 101B in FIG. 2A connected in a three phase configuration having appropriate control logic 30C to trigger the event needed to provide a three-phase waveform to the machine 40A. Batteries B.sub.A and B.sub.B are in a battery section 26 that further includes a battery B.sub.1-2 that can be the same as the two batteries B.sub.1 and B.sub.2 in FIG. 2A. All three phases of the synthesizer 101C are powered by the battery unit 26. The synthesizer comprises units 98C.sub.1 and 99C.sub.1 that are respectively the positive-going and negative-going units (like units 98B and 99B, respectively, in FIG. 2A) that power phase A of the machine 40A through a mixer 20'.sub.A units 98C.sub.2 and 99C.sub.2 that power phase B through a mixer 20'.sub.B and units 98C.sub.3 and 99C.sub.3 that power phase C through a mixer 20'.sub.C. The representation of FIG. 7 is essentially self-explanatory in the light of the detailed explanation above. The three-phase stator winding only of the machine 40A is shown; it, of course, has a rotor which may be a dc field making the machine 40A a synchronous machine, motor or alternator. In one use the machine may be employed to drive an electric vehicle and power flow may be to the synthesizer from the machine 40A or from the synthesizer to the machine 40A. In either event, power can be accepted or delivered in a controlled fashion by amplitude modulation of the rms voltage in the way described above. It will be appreciated, also, without further explication, that the machine 40A can be an alternator alone to effect charging of the batteries B.sub.A, B.sub.B and B.sub.1-2. Further, in an electric vehicle system the machine 40A acts both as a motor and as a generator and the synthesizer 101C regulates energy flow, both as to the level of such flow and the direction thereof.

The system numbered 103 in FIG. 8 is another rotating electronic machine that has a multi-coil (i.e., six-coil) winding 43, comprising coils 44A . . . 44F, of a rotating electric machine 40B. The winding 43 is energized by synthesizers 101.sub.1 . . . 101.sub.6, each of which can be similar to the synthesizer 101B in FIG. 2A, connected to winding nodes 45A . . . 45F, respectively, to control energy transfer between the machine 40B and the synthesizers 101.sub.1 . . . 101.sub.6. A mechanical position indicator and logic 42 notes the position of a rotor 41 (which is shown as a permanent magnet) to provide appropriate switching signals to the synthesizers 101.sub.1 . . . 101.sub.6. (By way of background for closed loop windings of the type shown in FIG. 8, attention is called to U.S. Letters Pat. No. 3,909,684 (Smith, Jr.) and 3,619,746 (Thornton et al.)) Again, the machine 40B can operate in a motoring mode and/or in a generating mode.

The explanation now with reference to FIGS. 9A and 9B should be read keeping in mind the above discussion as well as the Kirtley et al application since, like the latter, the system shown at 102E in FIG. 9A is an electronic motor that comprises an electronic waveform synthesizer 101E and a polyphase rotating electric machine comprising coils L.sub.1 and L.sub.2 (i.e., the coils L.sub.1 and L.sub.2 form the two-phase winding of a polyphase machine which may have a squirrel cage rotor--not shown--for example). The synthesizer 101E, as later explained, consists of two single-stage units 98E and 99E whose outputs are connected to electronic mixer means 20E.

The electronic mixer means 20E consists of a first mixer section 20E.sub.A and a second mixer section 20E.sub.B. The section 20E.sub.A includes thyristors SCR.sub.1AA and SCR.sub.1BA connected back-to-back with diodes D.sub.1-AA and D.sub.1-BA, respectively; the section 20E.sub.B includes thyristors SCR.sub.1AB and SCR.sub.1BB connected back-to-back with diode D.sub.1-AB and D.sub.1-BB, respectively. The thyristors SCR.sub.1AA and SCR.sub.1BA are rendered active and inactive by signals carried by a conductor 15A that connects the gates thereof to control logic 30E; the gates of the thyristors SCR.sub.1AB and SCR.sub.1BB are connected to the logic 30E by a conductor 15B. (Generally the conductors 15A and 15B, as well as the conductor 15 before discussed, are a plurality of conductors.)

The system 102E is connected to receive input power from a single phase source 97 (which may be the single phase 120/240 volt input to a house, say, from the power company; G indicates the neutral connection and can be actual earthing); the coil L.sub.1 is connected across the outside leads shown at 21 and 22 of the source 97 (which leads are usually 240 volts in the conventional systems in the United States) and the coil L.sub.2 is connected between the first mixer section 20E.sub.A and the second mixer section 20E.sub.B ; that is, the coil L.sub.2 is connected to receive the outputs labeled M.sub.E and M'.sub.E of sections 20E.sub.A and 20E.sub.B, respectively, the inputs to the sections being the outputs of the units 98E and 99E. The inputs to the units 98E and 99E are from the source 97 through a full wave rectifier comprising diodes D.sub.1E . . . D.sub.4E.

The unit 98E includes a capacitor C.sub.1-1E and a bilateral switch S.sub.1AE ; the unit 99E includes a capacitor C.sub.1-1E and a bilateral switch S.sub.1BE. It will be appreciated that the switch S.sub.1AE can be identical to the combined switch S.sub.1-1A and S.sub.2-1A of FIG. 1 and the switch S.sub.1BE can be identical to the combined switch S.sub.1-1B and S.sub.2-1B. The control logic 30E controls the stage switches S.sub.1AE and S.sub.1BE along with the mixer thyristors, in an appropriate fashion to synthesize the waveform shown at 81E in FIG. 9B, which is the waveform applied to the coil L.sub.2. It can be shown that appropriate switching of the switches S.sub.1AE and S.sub.1BE together with the thyristors in the mixer 20E will provide the two-step waveform 81E. It will be appreciated that each unit 98E and 99E can consist of more than one stage to increase the number of steps in the waveform, that the widths of the steps can be changed to modify the rms voltage, as before, and that each step can be composed of multi-pulses, as before. The batteries B.sub.1 and B.sub.2 serve to reverse bias the thyristors in the same way that the like batteries in FIG. 2A perform.

A number of further matters with regard to the embodiment of FIG. 9A are contained in this paragraph. It will be appreciated that the inductance of the coil L.sub.2 is such that a path must be provided for the current flow in the coil during switching of the various semiconductor devices in the synthesizer 101E; such a path is provided by the diodes D.sub.1-AA . . . in the mixer 20E and the unmarked diodes (which correspond to the diodes D.sub.1-1 . . . of FIG. 1) associated with the switches S.sub.1AE and S.sub.1BE all of which perform as freewheeling diodes in the synthesizer. The capacitor C.sub.1-1E and C'.sub.1-1E operate mostly in a dc voltage mode, that is, the voltage across the capacitor terminals does not change polarity; hence, these capactors are operated in a dc mode and can be smaller than the ac capacitors of the same KVA rating that are used in conventional single-phase capacitor start/and/or run motors that the system of FIG. 9A is intended to replace. The polyphase machine in FIG. 9A is a two-phase machine, and the synthesizer 101E serves to shift the phase of the incoming voltage about 90 electrical degrees as discussed in the Kirtly et al application. It will be appreciated that the shift in time phase can be other than 90 electrical degrees and that the system 101E can be used, say, to power a three-phase motor in an open delta system in the manner described in the Kirtley et al application. The batteries B.sub.1 and B.sub.2 in FIG. 9A like the similarly labeled elements in FIG. 2A constitute low voltage means to provide the voltage .DELTA.V that serves to back bias the thyristors SCR.sub.1AA . . . ; again, the batteries are connected through the stage switches (here switches S.sub.1AE and S.sub.1BE) to provide a reverse bias to the thyristors at an appropriate time in the cycle of the synthesizer in the manner previously discussed herein.

The synthesizer shown at 101F in FIG. 10 is like the synthesizer 101E; units 98F and 99F can be identical to the units 98E and 99E and mixer 20F can be identical to the mixer 20E; and the output waveform at outputs M.sub.F and M'.sub.F can be identical to the waveform 81E and can be modified in the same manner as the waveform 81E. The disclosure of FIG. 10 is intended to show a different arrangement 32 (i.e., different low voltage means) for effecting back biasing of the thyristors in the mixer 20F; that is, another way to provide the low voltage .DELTA.V referred to earlier herein. The low voltage means 32 includes a transformer 31, full-wave rectifying diodes D.sub.1F . . . D.sub.4F and a capacitor C.sub.3F. The transformer 31 can be a filament transformer; the polarities are indicated. The control logic marked 30F can be digital logic to perform the same functions as the logic discussed previously herein.

The electronic synthesizer designated 101G in FIG. 11 comprises a plurality of stages, Stage 1 . . . Stage N, connected in cascade, each stage comprising dc or unidirectional supply voltage means B.sub.1G . . . B.sub.NG and bilateral stage switch means S.sub.1-G - S.sub.2-1G . . . S.sub.1-NG - S.sub.2-NG, the bilateral stage switch means serving to control electric current flow in the dc or unidirectional supply voltage means of the stage as well as to effect an electrical bypass of the dc or unidirectional supply voltage means of the stage. See said patent 3,867,643 (Baker et al). Control logic 30G activates the bilateral switch S.sub.1-G to provide as output to a load a waveform, for example, like any of the waveforms of FIGS. 3A - 3G or those of FIGS. 5B - 5K. In other words, the logic 30G, which may be a slightly modified version of the logic in FIG. 6 hereof, is operable to control the rms value of the voltage waveform from the synthesizer 101G as well as the harmonic content thereof, the synthesized waveform, as before, being generated as steps whose widths are modified to affect the rms value and harmonic content and, if desired or required, each step being synthesized as a plurality of pulses whose pulse width is much less than half the wavelength of the ac waveform synthesized, at least one of pulse width and pulse timing being controlled by the control logic means 30G to establish an acceptable level of harmonic distortion in the waveform thereby synthesized.

Further modifications of the invention herein described will occur to persons skilled in the art and all such modifications are deemed to be within the spirit and scope of the invention as defined by the appended claims.