Voltage waveform synthesizer and a system that includes the same

• US 4,117,364 A
• Filed: 05/14/1976
• Issued: 09/26/1978
• Est. Priority Date: 05/14/1976
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Baker, Richard H.
• Primary Examiner(s): Hohauser, Herman J.
• Application Number:
  US05/686,438
• Time in Patent Office: 865 Days
• Field of Search: 318/230, 318/231, 318/227, 363/124, 363/135, 363/136, 363/137, 363/138, 363/43, 363/41
• US Class Current: 318/810
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: H02P 27/06 using dc to ac converters or inverters H02P27/05 takes precedence

Abstract

A voltage waveform synthesizer whereby an ac waveform (which may be varied in frequency) is synthesized from dc or unidirectional voltages in a programmable fashion, the power carried by the waveform being controllable from zero to some maximum value and the harmonic content of the waveform also being controllable. The synthesizer per se is described and it is shown in combination with a rotating electric machine to provide, for example, a variable speed drive mechanism.

Claims

1. An electronic waveform synthesizer having, in combination:

a first unit comprising a stage that includes dc or unidirectional supply voltage means whose output voltage is at the amplitude E and bilateral stage switch means, the bilateral stage switch means serving to control electric current flow in the dc or unidirectional supply voltage means of the stage and serving as well to effect an electrical bypass of the dc or unidirectional supply voltage means of the stage;

a second unit comprising a stage that includes dc or unidirectional supply voltage means whose output voltage is at the amplitude E and bilateral stage switch means, the bilateral stage switch means serving to control electric current flow in the dc or unidirectional supply voltage means of the stage and serving as well to effect an electrical bypass of the dc or unidirectional supply voltage means of the stage;

electronic mixer means connected to the first unit and the second unit, said electronic mixer means comprising a plurality of bilateral mixer switches connected to receive the dc or unidirectional electric potential of the dc or unidirectional supply voltage means of the stage of each unit and operable to process the same in a determined and programmable fashion so that there appears at an output port of the electronic waveform synthesizer a waveform that is alternating in nature even though the supply voltage means of each stage and each unit is dc or unidirectional in nature the output of the electronic mixer means being the output that appears at said output port; and

control logic means that serves to activate the bilateral stage switch means of both the first unit and the second unit, as well as the electronic mixer switch means, in a programmable fashion.

2. An electronic waveform synthesizer as claimed in claim 1 in which the electronic mixer means operates to mix the outputs of the first unit and the second unit to provide an alternating output waveform from the synthesizer that is successively the output of the first unit, then the output of the second unit, then the output of the first unit, and so forth.

3. An electronic waveform synthesizer as claimed in claim 2 wherein each bilateral mixer switch comprises a thyristor and a diode connected in opposite polarity, the synthesizer including low voltage means to reverse bias the thyristor.

4. An electronic waveform synthesizer as claimed in claim 1 the output waveform of the synthesizer is a stepped wave whose steps are variable over a wide range to affect the rms voltage of the output waveform and wherein the control logic means comprises digital logic means that accepts a number that, in turn, determines the width of the steps that form the waveform.

5. An electronic waveform synthesizer as claimed in claim 4 wherein the digital logic means includes resettable up/down counter means that receives the number and provides a count up and a count down that is a function of the number which establishes the step width on the basis of the number so received.

6. An electronic waveform synthesizer as claimed in claim 1 wherein each said unit comprises a plurality of stages as defined by claim 1 connected in cascade and wherein the control logic means serves to program the interconnection of the voltage supply means of the stages of each unit as well as to combine the units to provide an output waveform.

7. An electronic waveform synthesizer as claimed in claim 6 wherein the dc or unidirectional supply voltage means of the first stage of the plurality of stages of each unit is a battery and the supply voltage means of each successive stage is a capacitor.

8. An electronic waveform synthesizer as claimed in claim 7 wherein the battery in said first stage is rechargeable and wherein the control logic means serves to permit power flow into the electronic waveform synthesizer as well as out of the electronic waveform synthesizer.

9. An electronic waveform synthesizer as claimed in claim 1 wherein the dc or unidirectional supply voltage means is a battery.

10. An electronic waveform synthesizer as claimed in claim 1 wherein the dc or unidirectional supply voltage means is a capacitor.

11. An electronic waveform synthesizer as claimed in claim 1 wherein the dc or unidirectional supply voltage means is a solar cell or a fuel cell.

12. Apparatus that comprises a plurality of electronic waveform synthesizers as claimed in claim 1 and that further includes a variable-speed rotating electric machine connected to receive an input thereto the output of the plurality of electronic waveform synthesizers that serves as an N-phase polyphase supply for said machine.

13. Apparatus that comprises a plurality of electronic waveform synthesizers as claimed in claim 1 that further includes a variable-speed rotating electric machine connected to receive as input thereto the output of the plurality of electronic waveform synthesizers, wherein the machine comprises an armature winding having an even number of coils connected in a closed loop configuration with a winding node between adjacent coils and wherein an electronic waveform synthesizer of said plurality is connected to each winding node to introduce electric current to the node and to receive electric current from the node, the control logic means being operable to control the flow of current at the nodes such that in an operating system a rotating magnetic field is generated in said machine.

14. An electronic waveform synthesizer as claimed in claim 1 in which the control logic means cycles the bilateral stage switch means and the bilateral mixer switch means such that the waveform synthesized comprises a plurality of pulses whose voltages are at the amplitude E and whose pulse widths are much narrower than one-half cycle of the waveform, the occurrence of the pulses being timed to affect the harmonic content of the waveform.

15. An electric waveform synthesizer as claimed in claim 14 wherein the widths of the pulses that make up the waveforms are controlled also to affect the harmonic content.

16. Apparatus that comprises a plurality of electronic waveform synthesizers as claimed in claim 1 and that further includes a rotating electric machine, the waveform synthesizers and the rotating electric machine being interconnected to permit electric power transfer therebetween.

17. Apparatus as claimed in claim 16 wherein the control logic means cycles the bilateral stage switch means and the bilateral mixer switch means such that the waveform synthesized by each electronic waveform synthesizer of said plurality produces a quasi-sinusoidal waveform square or stepped waves, said control logic means acting to vary the widths of the steps that form the quasi-sinusoidal waveform over a wide range to control the rms voltage and hence the power transfer between the plurality of waveform synthesizers and the rotating electric machine.

18. Apparatus as claimed in claim 17 wherein said rotating electric machine is an electric motor and wherein the synthesizer varies the frequency of the waveform delivered thereto, and thus the speed of the motor, as well as the electrical power transfer thereto.

19. Apparatus as claimed in claim 17 wherein said rotating electric machine receives electric power from the plurality of waveform synthesizers in a motoring mode of operation and in which said rotating electric machine delivers electric power from the plurality of waveform synthesizers in a generating mode of operation.

20. Apparatus as claimed in claim 17 wherein said wide range is between some maximum value and zero.

21. Apparatus as claimed in claim 17 wherein each half of the quasisinusoid thus synthesized by each synthesizer of said plurality comprises a plurality of pulses whose pulse widths, spacings and/or number are controlled and varied over said range to affect the harmonic content of the waveform thus synthesized.

22. An electronic waveform synthesizer as claimed in claim 1 in which the control logic means cycles the bilateral stage switch means and the bilateral mixer switch means such that the waveform synthesized comprises a quasi-sinusoid synthesized as stepped waves, the widths of the steps that form the quasi-sinusoidal waveform being variable over a wide range to control the rms voltage and hence the power that can be delivered to a load.

23. An electronic waveform synthesizer as claimed in claim 22 wherein said wide range is from some maximum value to zero.

24. An electronic wavefory synthesizer as claimed in claim 22 wherein each half of the quasi-sinusoid thus synthesized comprises a plurality of pulses whose pulse widths, spacings and/or number are controlled and varied over said range to affect the harmonic content of the waveform thus synthesized.

25. An electronic waveform synthesizer as claimed in claim 22 wherein each half of the quasi-sinusoid thus synthesized comprises a plurality of pulses, at least one of pulse width, pulse spacing and number of pulses being controlled to affect the harmonic content of the waveform thus synthesized.

37. An electronic waveform synthesizer as claimed in claim 3 in which the low voltage means comprises an electrical bridge configuration that includes a source of positive and negative electric potential connected through the bilateral stage switch means of the first unit and the bilateral stage switch means of the second unit to the thyristors of the bilateral mixer switches that serve to connect the appropriate low voltage reverse bias to the thyristor of each bilateral mixer switch.

38. An electronic waveform synthesizer as claimed in claim 37 wherein the first unit is a positive unit that presents a positive voltage waveform to the mixer means in an operating system and the second unit is a negative unit that presents a negative voltage waveform to the mixer means, and wherein the mixer means includes a pair of thyristors serially connected, the anode of one thyristor being connected through the stage switch means of the first unit to the point of positive electric potential and the cathode of the other thyristor being connected through the stage switch means of the second unit to said point of negative potential.

39. An electronic waveform synthesizer as claimed in claim 37 wherein the mixer means includes two pairs of thyristors serially connected, the serial connection of each pair serving as a connection to the synthesizer to receive a load which is connected between the two serial connections, each thyristor pair having the anode of one thyristor of the pair connected through the stage switch means of the first unit to said point of negative potential and the cathode of one thyristor of the pair connected through the stage switch means of the second unit to said point of negative potential.

26. An electronic ac waveform synthesizer having, in combination:

a plurality of stages, each stage comprising dc or unidirectional supply voltage means and bilateral stage switch means, 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; and

control logic means that serves to activate the bilateral stage switch means to determine the shape of said ac waveform, the control logic means controlling the switching of the bilateral stage switch means such that the waveform synthesized comprises a plurality of steps forming each half wavelength thereof, the steps that form each half wavelength of the synthesized ac waveform comprising substantially fixed amplitude pulses whose pulse widths are much less than half the wavelength of the ac waveform synthesized, at least one of the pulse width and the pulse timing being controlled by the control logic means to establish an acceptable level of harmonic content in the waveform.

27. An electric waveform synthesizer as claimed in claim 26 that further includes electric mixer means connected to receive the waveform from the plurality of stages, said electric mixer means comprising a plurality of bilateral mixer switch means connected to receive a dc or unidirectional electric potential from the plurality of stages and operable to process the same in a determined and programmable fashion so that there appears at the output port of the electronic synthesizer a waveform that is alternating in nature even though the electric potential from the plurality of stages is dc or unidirectional in nature, the harmonic content of the alternating waveform being determined under the direction of the control logic means.

28. An electric waveform synthesizer as claimed in claim 26 wherein the bilateral stage switch means of each stage is capable of reversing the polarity between ports of the stage and wherein the control logic means of the plurality of stages serves to produce at the output of the synthesizer a waveform that is alternating in nature and which contains an acceptable level of harmonic content.

40. An electronic waveform synthesizer as claimed in claim 26 in which the control logic means comprises digital logic means comprising counters operable to operate in an up/down counter sequence wherein the down counter is the mirror image of the up count to provide automatic timing symmetry.

41. An electronic waveform synthesizer as claimed in claim 26 wherein the pulses that form each half of the ac waveform are many in number.

42. An electronic waveform synthesizer as claimed in claim 26 in which the bilateral stage switch means and the control logic means interact to interconnect the dc or unidirectional supply voltage means of the plurality of stages to provide a variable frequency waveform whose frequency is variable over a wide range of frequencies and whose harmonic content is controllable, in part, over said wide range of frequencies by control of at least one of the width and timing of said pulses.

29. An electronic rotating machine that comprises, in combination:

a plurality of electronic waveform synthesizers each of which comprises a plurality of stages, each stage comprising dc or unidirectional supply voltage means and bilateral stage switch means, 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, and control logic means that serve to activate the bilateral stage switch means to determine the shape of said waveform, the control logic means controlling the switching of the bilateral stage switch means such that the waveform synthesized is quasi-sinusoidal and comprises square waves whose widths are variable over a wide range to control the rms voltage of the waveform and hence the power delivered by the synthesizers, each half cycle of the wave synthesized comprising a plurality of said square waves, which square waves comprise many pulses whose widths are much less than the half wavelength of the synthesized at least one of the pulse width and the pulse timing being controlled by the control logic means to establish an acceptable level of harmonic content in the waveforms; and

a polyphase rotating electric machine connected to the plurality of waveform synthesizers.

30. An electronic rotating machine as claimed in claim 29 in which the rotating electric machine is an electric motor whose speed is controlled by varying the frequency of the waveforms synthesized and in which the electric power transfer between the plurality of synthesizers and the electric motor is regulated by regulating the width of said square waves.

31. An electronic rotating machine as claimed in claim 29 in which the polyphase rotating electric machine is adapted to perform motoring functions as well as generating functions and in which the control logic means and the plurality of waveform synthesizers interact to permit interchange of energy in either directions between the synthesizers and the polyphase rotating electric machine as well as to monitor the electrical power transfer therebetween.

32. An electronic alternating waveform synthesizer having, in combination, dc or unidirectional supply voltage means comprising a plurality of dc or unidirectional electric power supplies, switch means operable to connect the dc or unidirectional power supplies to an output port of the synthesizer, control logic means connected to activate the switch means in a programmable fashion so that there appears at said output port an electric waveform that is alternating in nature even though the supply voltage means is dc or unidirectional in nature, each half cycle of the waveform being formed solely of a plurality of steps or square waves of electric energy from the dc or unidirectional supply voltage means, said control logic means being adapted to control the width of said steps or square waves to monitor the interchange of electric energy at said port, each half-cycle of the waveform synthesized comprising many substantially fixed amplitude pulses, at least one of pulse width and pulse timing being controllable by the control logic means to establish an acceptable level of harmonic content in the waveform, the control logic means being operable to control the switch means to generate said pulses with pulse widths of the pulses forming each half-cycle much less than half the wavelength of the ac waveform synthesized.

33. An electronic alternating waveform synthesizer as claimed in claim 32 in which the control logic means controls the switch means to interconnect, the plurality of dc or unidirectional power supplies to provide said alternating waveform in the form of multiple steps in each half cycle thereof, said steps comprising said pulses and in which the frequency of the waveform is variable from about zero to some frequency much greater than zero.

34. Apparatus that comprises, in combination:

a polyphase load and a voltage waveform synthesizer interconnected to permit the apparatus to connect to a single phase line, one phase of the polyphase load being adapted to connect directly to the single phase line and another phase thereof being connected through the voltage waveform synthesizer to the single phase line, said synthesizer comprising a first unit comprising a stage that includes dc or unidirectional supply voltage means and bilateral stage switch means, the bilateral stage switch means serving to control electric current flow in the dc or unidirectional supply voltage means of the stage and serving as well to effect an electrical bypass of the dc or unidirectional supply voltage means of the stage, a second unit comprising a stage that includes dc or unidirectional supply voltage means and bilateral stage switch means, the bilateral stage switch means serving to control electric current flow in the dc or unidirectional supply voltage means of the stage and serving as well to effect an electrical bypass of the dc or unidirectional supply voltage means of the stage, electronic mixer means connected to the first unit and the second unit, said electronic mixer means comprising a plurality of bilateral mixer switches connected to receive the dc or unidirectional electric potential of the dc or unidirectional supply voltage means of the stage of each unit and operable to process the same in a determined and programmable fashion so that there appears at an output port of the electronic waveform synthesizer a waveform that is alternating in nature even though the supply voltage means of each stage and each unit is dc or unidirectional in nature, and control logic means that serves to activate the bilateral stage switch means of both the first unit and the second unit, as well as the electronic mixer switch means, in a programmable fashion.

35. Apparatus as claimed in claim 34 wherein the polyphase load is a polyphase rotating machine.

36. Apparatus as claimed in claim 35 wherein the polyphase rotating machine is a two-phase electric motor one phase of which is adapted to connect directly across the single-phase line and the other phase of which is connected to the synthesizer which serves as a phase shifter.

43. An electronic waveform synthesizer having, in combination a plurality of dc sources, switch means operable to connect the plurality of dc sources to an output port of the synthesizer, control logic means connected to activate the switch means in a programmable fashion so that there appears at said output port and electric waveform as a plurality of square waves of electric energy formed solely by combining the dc sources, said control logic means being operable to control the width of said square waves and being operable, as well, to form a square wave of a plurality of fixed amplitude pulses, at least one of pulse width and pulse timing being controllable by the control logic means to establish an acceptable level of harmonic content in said square wave, the control logic means being operable to control the switch means to generate said pulses with pulse widths of the pulses forming said square wave much less than the width of the square wave.