Series resonance charge transfer regulation method and apparatus

• US 4,523,269 A
• Filed: 11/16/1983
• Issued: 06/11/1985
• Est. Priority Date: 11/16/1983
• Status: Expired due to Fees

• Current Assignee: Reliance Electric Company (ABB Limited)
• Original Assignee: Reliance Electric Company (ABB Limited)
• Inventors: Baker, Richard H., Chambers, Derek, Chu, David L.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): REBSCH, DONALD
• Application Number:
  US06/552,335
• Time in Patent Office: 573 Days
• Field of Search: 307/110, 320/1, 363/17, 363/43, 363/96, 363/97, 363/98, 363/136, 363/137, 363/138
• US Class Current: 363/138
• CPC Class Codes: H02M 5/14 for conversion between circuits of different phase number
• CPC Class Codes: H02M 5/2576 with digital control
• CPC Class Codes: H02M 7/4826 operating from a resonant DC source, i.e. the DC input voltage varies periodically, e.g. resonant DC-link inverters

Abstract

A DC to N phase AC converter, where N is an integer greater than 2, includes a DC source having first and second terminals for deriving equal amplitude opposite polarity DC voltages, a series resonant circuit, and N output terminals, one for each phase of the converter. The series resonant circuit is selectively connected in series with the first and second terminals and the N output terminals for an interval equal to one half cycle of the resonant circuit resonant frequency, so that current flows between a selected one of the first and second terminals and the resonant circuit and a selected one of the N output terminals during the interval. The resonant circuit current is zero at the beginning and end of the interval. A capacitor shunting each of the output terminals has a value relative to the capacitance of the series resonant circuit such that the voltage across each output terminal remains approximately constant between adjacent exchanges of energy between the resonant circuit and the output terminal. The selective connection is in response to a comparison of the actual voltage across each of the N output terminals and a reference voltage for each of the N output terminals. The comparison controls when the flow of current between the selected first and second terminals and the selected output terminal via the resonant circuit begins. The frequency of the AC voltage developed across the N output terminals is much less than the resonant frequency of the circuit.

Claims

1. A method of regulating a load so it has a predetermined voltage, the load being regulated with a resonant circuit selectively connected between the load and a source, the resonant circuit including a series capacitor, the load including a shunt capacitor having a value such that the load voltage remains relatively constant between adjacent exchanges of energy between the resonant circuit and to the load, comprising charging the series capacitor to a level determined by the source voltage and the voltage across the shunt capacitor, and connecting the source in series with the load and the resonant circuit while the series capacitor is charged to said level for an interval equal to one half cycle of the resonant circuit resonant frequency so current flowing between the source and the load via the resonant circuit during the interval is zero at the beginning and end of the interval.

2. The method of claim 1 further including the step of instigating the flow of said current between the source and the load via the resonant circuit at a time determined by the relative amplitudes of the load voltage and the predetermined voltage.

3. The method of claim 1 wherein the series capacitor is charged to the level by a DC voltage source for a period having a duration equal to the interval so that the resonant circuit current is zero at the beginning and end of the period and approximately all of the charge subsisting across the capacitor at the end of the period subsists across the capacitor at the beginning of the interval.

4. The method of claim 3 wherein the DC voltage source for charging the series capacitor during the period has a polarity that is the same as the polarity of the DC source connected to the resonant circuit during the interval.

5. A method of regulating a load so it has a predetermined voltage, the load being regulated with a resonant circuit selectively connected between the load and a source, the resonant circuit including a series capacitor, the load including a shunt capacitor having a value such that the load voltage remains relatively constant between adjacent exchanges of energy between the resonant circuit and the load, comprising connecting the source in series with the resonant circuit and the load for an interval equal to one half cycle of the resonant circuit resonant frequency so current flowing between the source and the load via the resonant circuit during the interval is zero at the beginning and end of the interval, the flow of said current between the source and the resonant circuit to the load being instigated at a time determined by the relative amplitudes of the load voltage and the predetermined voltage.

6. A DC to N phase AC converter, where N is an integer greater than 2, comprising a DC source having first and second terminals for deriving opposite polarity DC voltages, a series resonant circuit, N output terminals, one for each phase of the converter, means for selectively connecting the series resonant circuit in series with the first and second terminals and the N output terminals for an interval equal to one half cycle of the resonant circuit resonant frequency so current flows between a selected one of the first and second terminals and the resonant circuit and a selected one of the N output terminals during the interval, the resonant circuit current being zero at the beginning and end of the interval, a capacitor shunting each of the output terminals, each shunt capacitor having a value relative to the capacitance of the series resonant circuit so that the voltage across each output terminal remains approximately constant between adjacent exchanges of energy between the resonant circuit and the output terminal, means responsive to the actual voltage across each of the N output terminals and a reference voltage for each of the N output terminals for controlling said means for selecting and for controlling the time of instigating the flow of said current between the selected first and second terminals and the selected output terminal via the resonant circuit, the frequency of the AC voltage developed across the N output terminals being much less than the resonant frequency of the resonant circuit.

7. The converter of claim 6 wherein the means for controlling activates the means for selecting so the resonant circuit capacitance is charged, prior to application of energy to the selected output terminal, to a level determined by the voltage across the selected output terminal so that at the beginning of the interval the capacitance is charged to the level.

8. The converter of claim 7 wherein the means for controlling activates the means for selecting to connect the selected output terminal to the source terminal having a polarity opposite to the selected source terminal, the connection subsisting for a period having a duration equal to the interval so that the resonant circuit current is zero at the beginning and end of the period and approximately all of the charge subsisting across the capacitor at the end of the period subsists across the capacitor at the beginning of the interval.

9. The converter of claim 6 wherein the voltages at the first and second terminals have the same magnitude.

10. A DC to AC converter comprising a DC source having first and second terminals for deriving opposite polarity DC voltages, a series resonant circuit, an output terminal across which the AC is developed, means for selectively connecting the series resonant circuit in series with the first and second terminals and the output terminal for an interval equal to one half cycle of the resonant circuit resonant frequency to apply current from a selected one of the first and second terminals and the resonant circuit to the output terminal during the interval so that the resonant circuit current is zero at the beginning and end of the interval, a capacitor shunting each of the output terminal, each shunt capacitor having a value relative to the capacitance of the series resonant circuit so that the voltage across the output terminal remains approximately constant between adjacent exchanges of energy between the resonant circuit and the output terminal, means responsive to the voltage across the output terminal and a value for a reference voltage for the output terminal for controlling said means for selecting and for controlling the time of instigating the flow of said current between the selected first and second terminals and to the selected output terminal via the resonant circuit, the frequency of the AC voltage developed across the N output terminals being much less than the resonant frequency of the resonant circuit.

11. The converter of claim 10 wherein the means for controlling activates the means for selecting so the resonant circuit capacitance is charged, prior to application of energy to the selected output terminal, to a level determined by the voltage across the output terminal so that at the beginning of the interval the capacitance is charged to the level.

12. The converter of claim 10 wherein the means for controlling activates the means for selecting to connect the output terminal to the source terminal having a polarity opposite to the selected source terminal for a period having a duration equal to the interval so that the resonant circuit current is zero at the beginning and end of the period and approximately all of the charge subsisting across the capacitor at the end of the period subsists across the capacitor at the beginning of the interval.

13. Apparatus for converting DC to AC comprising a DC source having equal amplitude and opposite polarity first and second DC terminals, first and second AC output terminals on which are simultaneously derived opposite polarity AC voltages, an output capacitor shunting each of the output terminals, a series resonant circuit, each of the output capacitors having a capacitance much greater than capacitance of the resonant circuit so that voltage established on the output capacitance has a tendency to remain constant over a period equal to many resonant frequency cycles of the resonant circuit, and means for connecting the resonant circuit to the first and second DC terminals and to the first and second output terminals for intervals having equal durations so first and second opposite polarity half sinusoidal power pulses having zero initial and final currents alternately flow relative to the first and second AC output terminals respectively, said connecting means establishing a charge that is a function of the DC source voltage amplitude and the voltage across the output terminal through which the next power pulse flows.

14. The apparatus of claim 13 wherein the means for connecting establishes the charge immediately prior to the first and second power pulses by connecting the second and first DC terminals to the resonant cicuit while the resonant circuit is respectively connected to the first and second output terminals for equal intervals equal to the interval of one of the half sinusoidal pulses.

15. The apparatus of claim 13 further including a reference source for voltages at the output terminals, and means responsive to an error function of the voltages at the output terminals and the reference source for controlling the times when the first and second power pulses are supplied to the first and second terminals.

16. A method of converting DC to AC with a DC source having equal amplitude and opposite polarity first and second DC terminals, first and second AC output terminals on which are simultaneously derived opposite polarity AC voltages, an output capacitor shunting each of the output terminals, a series resonant circuit, each of the output capacitors having a capacitance much greater than capacitance of the resonant circuit so that voltage established on the output capacitance has a tendency to remain constant over a period equal to many resonant frequency cycles of the resonant circuit, the method comprising establishing a first charge on the resonant circuit capacitance that is a function of the DC source voltage amplitude and the voltage of the first output terminal, with the first charge established connecting the resonant circuit to the first DC terminal and first AC output terminal for an interval of one half a resonant frequency cycle of the resonant circuit so a half wave power pulse having zero initial and final currents and of a first polarity is coupled via the resonant circuit between the first DC terminal and the first AC output terminal, establishing a second charge on the resonant circuit capacitance that is a function of the DC source voltage amplitude and the voltage of the second output terminal, with the second charge established connecting the resonant circuit to the second DC terminal and second AC output terminal for an interval of one half a resonant frequency cycle of the resonant circuit so a half wave power pulse having zero initial and final currents and of a second polarity is coupled via the resonant circuit between the second DC terminal and the second AC output terminal.

17. The method of claim 16 wherein the first charge is established by connecting the resonant circuit to the second DC terminal and first AC output terminal for an interval of one half a resonant frequency cycle of the resonant circuit so a half wave charge establishing pulse having zero initial and final currents of the first polarity is coupled via the resonant circuit between the second DC terminal and the first AC output terminal, the second charge being established by connecting the resonant circuit to the first DC terminal and second AC output terminal for an interval of one half a resonant frequency cycle of the resonant circuit so a half wave charge establishing pulse have zero initial and final currents of the second polarity is coupled via the resonant circuit between the first DC terminal and the second AC output terminal.

18. The method of claim 17 further comprising initially charging the capacitance, prior to the first charge establishing pulse, to a voltage equal to twice the amplitude of the DC source, the voltage across the capacitance at the end of the second power pulse having the same amplitude and polarity as the voltage resulting from the initial charging and the voltage across the capacitance at the end of the first power pulse having the same amplitude and polarity opposite from the voltage resulting from the initial charging.

19. The method of claim 16 further including controlling the times when the first and second power pulses are coupled between the input and output terminals in response to an error function of the voltages across the output terminals relative to reference values therefor.

20. The method of claim 19 wherein the polarities of the reference values for the first and second output terminals differ, and controlling the polarity of the first and second power pulses in response to the polarity of the error function.

21. In a DC to AC converter including a series resonant circuit having a shuttle capacitor and a shuttle inductor for providing resonant current flow for charge transfer between DC voltage sources of +E and -E volts and selected ones of a plurality of output capacitors, whereby over successive cycles of operation of said converter said output capacitors are charged and discharged so desired voltage levels are derived across them at any given time, a method of operating said converter so voltage across said shuttle capacitor is naturally stabilized over a cycle of the converter operation, the voltage across the capacitor being reversed in polarity between absolute levels of 2E volts during each half-cycle of said converter by supplying a zero average current to the capacitor over each converter cycle of operation, the method comprising the steps of:

(1) providing a unidirectional current path during a first quarter cycle of the converter operation so resonant current flows between a first one of said +E and -E sources of voltage and a first one of said plurality of output capacitors through said series resonant circuit in a first direction;

(2) providing a unidirection current path during a second quarter cycle of the converter operator so resonant current flows between the or second one of said +E and -E sources of voltage and the first one of said plurality of output capacitors through said series resonant circuit in the first direction;

(3) providing a unidirectional current path during a third quarter cycle of the converter operation so resonant current flows between the first one of said +E and -E sources of voltage and the second one of said plurality of output capacitors through said series resonant circuit in a second direction;

(4) providing a unidirectional current path during a fourth quarter cycle of the converter operation so resonant current flows between the second one of said +E and -E sources of voltage and the second one of said plurality of output capacitors through said series resonant circuit in the second direction; and

,

repeating steps (1) through (4) to provide a frequency of operation of said converter that is no greater than one-half the resonant frequency of said series resonant circuit.

22. In a DC to AC converter including a series resonant circuit having a shuttle inductor and a shuttle capacitor for resonantly transferring energy between DC voltage sources of +E and -E volts and selected ones of a plurality of output capacitors, whereby over successive cycles of operation of said converter and output capacitors are charged and discharged to obtain desired levels of voltage across each one of said capacitors at any given time to obtain a desired conversion of said +E and -E voltages, said converter including means for naturally stabilizing the voltage across said shuttle capacitor between plus and minus 2E volts at any given time, the voltage polarity across the shuttle capacitor reversing during each half-cycle of said converter via said stabilization means maintaining zero average current flow through said shuttle capacitor over each cycle of operation of said converter, said stabilization means comprising:

first switching means for providing a unidirectional current path during a first quarter cycle of the converter operation for permitting resonant current to flow between a first one of said +E and -E sources of voltage and a first one of said plurality of output capacitors through said series resonant circuit in a first direction;

second switching means for providing a unidirectional current path during a second quarter cycle of the converter operation for permitting resonant current to flow between the second one of said +E and -E sources of voltage and the first one of said plurality of output capacitors through said series resonant circuit in the first direction;

third switching means for providing a unidirectional current path during a third quarter cycle of the converter operation for permitting resonant current to flow between a second one of said plurality of output capacitors and the second one of said +E and -E sources of voltage through said series resonant circuit in a second direction; and

fourth switching means for providing a unidirectional current path during a fourth quarter cycle of the converter operation for permitting resonant current to flow between the second one of said plurality of output capacitors and the first one of said +E and -E sources of voltage through said series resonant circuit in the second direction.

23. The converter of claim 22 wherein said first switching means includes:

first unidirectional current switching device means connected between one end of said series resonant circuit and said source of +E volts operable to a first and second conditions in which unidirectional current flows between said source of +E volts and said resonant circuit and for no current flows, respectively;

second unidirectional current switching device means connected between said one end of said series resonant circuit and said source of -E volts, operable to first and second conditions in which unidirectional current flows between said source of -E volts and said resonant circuit, and no current flows, respectively; and

a plurality of third unidirectional current switching device means each individually connected between the other end of said series resonant circuit and one end of said plurality of output capacitors, respectively, the other ends of said plurality of output capacitors being connected to a source of reference potential, each of said plurality of third unidirectional current switching device means being individually operable to first and second conditions in which unidirectional current flows between said other end of said series resonant circuit and its respective output capacitor, and no current flows, respectively.

24. The converter of claim 22 wherein said second switching means includes:

first unidirectional current switching device means connected between one end of said series resonant circuit and said source of +E volts operable to first and second conditions in which unidirectional current flows between said source of +E volts and said resonant circuit and no current flows, respectively;

second unidirectional current switching device means connected between said one end of said series resonant circuit and said source of -E volts, operable to first and second conditions in which unidirectional current flows between said source of -E volts and said resonant circuit, and no current flows, respectively; and

a plurality of third unidirectional current switching device means each individually connected between the other end of said series resonant circuit and one end of said plurality of output capacitors, respectively, the other ends of said plurality of output capacitors being connected to a source of reference potential, each of said plurality of third unidirectional current switching device means being individually operable to first and second conditions in which unidirectional current flows between said other end of said series resonant circuit and its respective output capacitor, and no current flows, respectively.

25. The converter of claim 22 wherein said third switching means includes:

a plurality of first undirectional current switching device means individually connected between one end of said series resonant circuit and one end of individual ones of said plurality of output capacitors, respectively, the other ends of said output capacitors being connected to a source of reference potential, each of said plurality of first unidirectional current switching device means being individually operable to first and second conditions in which unidirectional current flows between the respective output capacitor and said resonant circuit;

said unidirectional current switching device means connected between the other end of said series resonant circuit and said source of +E volts operable to first and second conditions in which unidirectional current flows between said series resonant circuit and said source of +E volts and no current flows, respectively; and

third unidirectional current switching device means connected between the other end of said series resonant circuit and said source of -E volts operable to first and second conditions in which unidirectional current flows between said series resonant circuit and said source of -E volts and no current flows, respectively.

26. The converter of claim 22 wherein said fourth switching means includes:

a plurality of first unidirectional current switching device means individually connected between one end of said series resonant circuit and one end of individual ones of said plurality of output capacitors, respectively, the other ends of said output capacitors being connected to a source of reference potential, each of said plurality of first unidirectional current switching device means being individually operable to first and second conditions in which unidirectional current flows between the respective output capacitor and said resonant circuit and no current flows, respectively;

second unidirectional current switching device means connected between the other end of said series resonant circuit and said source of +E volts operable to first and second conditions in which unidirectional current flows between said series resonant circuit and said source of +E volts and no current flows; and

third unidirectional current switching device means connected between the other end of said series resonant circuit and said source of -E volts, operable to first and second conditions in which unidirectional current flows between said series resonant circuit and said source of -E volts and no current flows, respectively.

27. The converter of claim 23 wherein each of said first, second and plurality of third unidirectional current switching device means includes a silicon-controlled-rectifier naturally commutated from a conducting to a non-conducting state in response to the magnitude of the resonant current flowing through it dropping substantially to zero.

28. The converter of claim 25 wherein said plurality of first unidirectional current switching device means, and said second and third unidirectional current switching device means each includes a silicon-controlled-rectifier naturally commutated from a conducting to a non-conducting state in response to the magnitude of the resonant current flowing through it dropping substantially to zero.

29. The converter of claim 23 whereby each of said first, second and plurality of third unidirectional current switching device means includes a power switching transistor.

30. The converter of claim 25 wherein each of said plurality of first unidirectional current switching device means, and said second and third unidirectional current switching device means includes a power switching transistor.

31. The converter circuit of claim 22 wherein said first switching means includes:

first unidirectional current switching device means connected between said series resonant circuit and said source of +E volts, operable to a first condition for unidirectionally conducting current from said source of +E volts to said series resonant circuit;

a diode having an anode electrode connected to said source of -E volts and a cathode electrode connected to said series resonant circuit for unidirectionally conducting current from said source of -E volts to said series resonant circuit;

a plurality of second unidirectional current switching device means each individually connected between said series resonant circuit and said plurality of output capacitors, respectively, said plurality of second unidirectional current switching device means each being individually operable to a first condition for unidirectionally conducting current from said series resonant circuit to an output capacitor connected thereto, and each having a second condition for preventing such flow of current.

32. The converter circuit of claim 22 wherein said second switching means includes:

first unidirectional current switching device means connected between said series resonant circuit and said source of +E volts, operable to a first condition for unidirectionally conducting current from said source of +E volts to said series resonant circuit;

a diode having an anode electrode connected to said source of -E volts and a cathode electrode connected to said series resonant circuit for unidirectionally conducting current from said source of -E volts to said series resonant circuit;

a plurality of second unidirectional current switching device means each individually connected between said series resonant circuit and said plurality of output capacitors, respectively, said plurality of second unidirectional current switching device means each being individually operable to a first condition for unidirectionally conducting current from said series resonant circuit to the output capacitor connected thereto, and each having a second condition for preventing such flow of current.

33. The converter circuit of claim 31 wherein said first unidirectional current switching device means includes a silicon-controlled-rectifier having an anode electrode connected to said source of +E volts and a cathode electrode connected to said series resonant circuit.

34. The converter circuit of claim 31 wherein each of said plurality of second unidirectional current device means includes a silicon-controlled-rectifier having an anode electrode connected to said series resonant circuit and a cathode electrode individually connected to said plurality of output capacitors.

35. The converter circuit of claim 31 wherein each of said first unidirectional switching device means and said plurality of second unidirectional current device means includes a power switching transistor.

36. The converter circuit of claim 22 wherein said third switching means includes:

first unidirectional current switching device means connected between said series resonant circuit and said source of -E volts, operable to a first condition for unidirectionally conducting current from said series resonant circuit to said source of -E volts;

a diode having a cathode electrode connected to said source of +E volts and an anode electrode connected to said series resonant circuit for unidirectionally conducting current from said series resonant circuit to said source of +E volts;

a plurality of second unidirectional current switching device means each individually connected betwen said series resonant circuit and said plurality of output capacitors, respectively, said plurality of second unidirectional current switching device means each being individually operable to a first condition for unidirectionally conducting current from said series resonant circuit to an output capacitor connected thereto, and each having a second condition for preventing such flow of current.

37. The converter circuit of claim 22 wherein said fourth switching means includes:

first unidirectional current switching device means connected between said series resonant circuit and said source of -E volts, operable to a first condition for unidirectionally conducting current from said series resonant circuit to said source of -E volts;

a diode having a cathode electrode connected to said source of +E volts and an anode electrode connected to said series resonant circuit for unidirectionally conducting current from said series resonant circuit to said source of +E volts;

a plurality of second unidirectional current switching device means each individually connected between said series resonant circuit and said plurality of output capacitors, respectively, said plurality of second unidirectional current switching device means each being individually operable to a first condition for unidirectionally conducting current from said series resonant circuit to the output capacitors connected thereto, and each having a second condition for preventing such flow of current.

38. The converter circuit of claim 36 wherein said first unidirectional current switching device means includes a silicon-controlled-rectifier having a cathode electrode connected to said source of -E volts and an anode electrode connected to said series resonant circuit.

39. The converter circuit of claim 36 wherein each of said plurality of second unidirectional current device means includes a silicon-controlled-rectifier having a cathode electrode connected to said other end of said series resonant circuit and an anode electrode individually connected to said plurality of output capacitors.

40. The converter circuit of claim 36 wherein each of said first unidirectional switching device means and said plurality of second unidirectional current device means includes a power switching transistor having a main current path polarized for unidirectional current flow in the desired direction.

41. In a cyclically operated charge transfer regulator converter including a series resonant circuit having a shuttle inductor and a shuttle capacitor, first and second power terminals connected to DC voltage sources having +E and -E output voltages, first and second output terminals connected to a load, a reference terminal connected to a reference potential, first and second output capacitors having first electrodes commonly connected to said reference terminal second electrodes connected to said first and second output terminals respectively, a method of operating said converter for resonantly conducting current between said +E and -E voltage sources and said first and second output terminals whereby current is coupled between a load connected to said output terminals and said sources to obtain a desired level of voltage across the load at any given time, the voltage across the shuttle capacitor reversing polarity during each half-cycle of said converter between absolute levels of 2E volts at the beginning and end of each half-cycle via the maintenance of a zero average magnitude of current flow over each cycle of operation of said converter, such method of operation of said converter over each cycle comprising the steps of:

(1) providing a unidirectional current path during a first quarter cycle of the converter operation so resonant of a first polarity current flows between a first one of said DC sources of voltage and a first one of said output terminals through said series resonant circuit;

(2) providing a unidirectional current path during a second quarter cycle of the converter operation so resonant current of the first polarity flows between the other DC source and the first output terminal through said series resonant circuit;

(3) providing a unidirectional current path during a third quarter cycle of the converter operation so resonant current of a second polarity flows between the second output terminal and the other DC source through said series resonant circuit;

(4) providing a unidirectional current path during a fourth quarter cycle of the converter operation so resonant current of the second polarity flows between the second output terminal and the first DC source through said series resonant circuit; and

repeating steps (1) through (4) for providing a frequency of operation of said converter that is substantially less than the resonant frequency of said series resonant circuit, each of said one-quarter cycles having a duration equal to one-half the period of one resonant frequency cycle of the resonant circuit.

48. The converter of claim 41 wherein each of said first, second, and third output switching means includes a pair of silicon-controlled-rectifiers connected in antiparallel.

42. A cyclically operated charge transfer regulator converter for converting DC to three phase AC, comprising:

first, second, and third output terminals;

a reference terminal connected to a reference potential;

first, second, and third output capacitors each having a first electrode connected to said reference terminal and second electrodes respectively connected to said first, second, and third output terminals;

first and second power terminals respectively connected to sources of DC voltages having levels of +E and -E volts;

a series resonant circuit including a shuttle inductor and a shuttle capacitor;

first and second input switching means respectively having first electrodes connected to said first and second power terminals and second electrodes having a common connection to said resonant circuit, said first and second input switching means each being operable to;

a first condition for providing a current path for unidirectional current flow of a first polarity between the power terminal associated therewith and said resonant circuit, a second condition for providing a current path for unidirectional current flow of a second polarity between said resonant circuit and the power terminal associated therewith, a third condition for preventing current flow therebetween;

first, second and third output switching means each having a main current path connected to said resonant circuit, each of said output switching means being respectively connected to said first, second and third output terminals and operable to;

a first condition for providing a current path for unidirectional current flow of the second polarity between said resonant cicuit and the associated output terminal, a second condition for providing a current path for unidirectional current flow of the first polarity between the associated output terminal and said resonant circuit, and a third condition for preventing current flow therebetween;

control means for operating said first and second input switching means and said first, second and third output switching means in predetermined, repetitive patterns over a number of operating cycles of said converter for (a) supplying current to a load connected to said first, second and third output terminals, and (b) selectively charging and discharging said first, second, and third output capacitors to obtain a desired level of voltage at the output terminals at any given time;

the sum of the voltages developed across said first, second and third output capacitors being zero at any given time, the voltage developed across said shuttle capacitor reversing polarity during each half-cycle of said converter operation between absolute levels of 2E volts at the beginning and end of each such half-cycle by maintaining a zero average magnitude of current flow over each cycle of operation of said converter, whereby for each such cycle, the operation of said first and second input switching means, and said first, second and third output switching means is such that over a first quarter cycle of converter operation a unidirectional current path is provided for current of the second polarity flowing between a first one of said power terminals sources and a first of said output capacitors, over a second quarter cycle of converter operation a unidirectional current path is provided for current of the second polarity flowing between the second power terminal and the first output capacitor, over a third quarter cycle of converter operation a unidirectional current path is provided for current of the first polarity flowing between a second of said output capacitors and the second power terminal, and over a fourth quarter cycle of converter operation a unidirectional current path is provided for current of the first polarity flowing between the second output capacitor and the first power terminal, the interval of each quarter cycle being approximately one-half the period of a resonant frequency cycle of said series resonant circuit.

43. The converter of claim 42 wherein each of said first and second input switching means includes a pair of silicon-controlled-rectifiers connected in antiparallel.

44. The converter of claim 42 wherein said first input switching means includes:

a first silicon-controlled-rectifier having anode and cathode electrodes respectively connected to said first power terminal and to said series resonant circuit; and

a first diode having cathode and anode electrodes respectively connected to said first power terminal and to said series resonant circuit.

45. The converter of claim 44 wherein said second input switching means includes:

a second silicon-controlled-rectifier having cathode and anode electrodes respectively connected to said second power terminal and to said series resonant circuit; and

a second diode having anode and cathode electrodes respectively connected to said second power terminal and to said series resonant circuit.

46. The converter of claim 42 wherein said first input switching means includes:

a first power switching transistor having a main current path connected between and polarized for unidirectionally conducting current from said first power terminal to said series resonant circuit; and

a first diode having a cathode electrode connected to said first power terminal and an anode electrode connected to said series resonant circuit.

47. The converter of claim 44 wherein said second input switching means includes:

a second power switching transistor having a main current path connected between and polarized for unidirectionally passing current from said series resonant circuit to said second power terminal; and

a second diode having an anode electrode connected to said second power terminal and a cathode electrode connected to said series resonant circuit.

49. A charge transfer regulator converter for converting DC to AC, comprising:

first and second output terminals connected to a load;

a reference terminal connected to a source of reference potential;

first and second output capacitors connected individually between said first output and reference terminals, and said second output and reference terminals, respectively;

first and second power terminals connected to sources of DC voltage having levels of +E and -E volts, respectively;

a series resonant circuit including a shuttle inductor and a shuttle capacitor;

first and second input switching means respectively connected to said first and second power terminals, said first and second input switching means having a common connection to one end of said resonant circuit, and being respectively operable to;

(a) a first condition for providing a current path for unidirectional current flow from the first and second power terminals to said resonant circuit, (b) a second condition for providing a current path for unidirectional current flow from said resonant circuit to the first and second power terminals, and (c) a condition for preventing current flow between the first and second power terminals and the resonant circuit;

first and second output switching means each having a common connection to said resonant circuit and respectively connected to said first and second output terminals, each of said first and second output switching means being respectively operable to;

(a) a first condition for providing a current path for unidirectional current flow from said resonant circuit to the first and second output terminals, (b) a second condition for providing a current path for unidirectional current flow from the first and second output terminals to said resonant circuit, and (c) an open circuit condition for preventing current flow between the first and second output terminals and the resonant circuit;

control means for operating said first and second input and output switching means in predetermined, repetitive patterns over a number of operating cycles of said converter for charging and discharging said first and second output capacitors to obtain a desired level of voltage therebetween at any given time and for supplying current to a load connected between said first and second output terminals, the voltage developed across said shuttle capacitor reversing polarity during each half-cycle of said converter operation between absolute levels of 2E volts at the beginning and end of each such half-cycle by maintaining a zero average current flow over each cycle of operation of said converter, whereby for each such cycle, the operation of said first and second input and output switching means is such that over a first quarter cycle of converter operation a unidirectional current path is provided for permitting current to flow in a first direction between a first of power terminals and a first of said output capacitors, over a second quarter cycle of converter operation a unidirectional current path is provided for permitting current to flow in the first direction between the other of said power terminals and the first output capacitor, over a third quarter cycle of converter operation a unidirectional current path is provided for permitting current to flow in the second direction between the other output capacitor and the second one of said power terminals, and over a fourth quarter cycle of the converter operation a unidirectional current path is provided for permitting current to flow in the second direction between the second output capacitor and the first power terminal, the duration of each one-quarter cycle of operation of said converter being approximately equal to one-half the period of one cycle of the resonant frequency of said series resonant circuit.

50. The converter of claim 49 wherein each of said first and second input switching means includes a pair of blocking silicon-controlled-rectifiers connected in antiparallel.

51. The converter of claim 49 wherein each of said first and second input switching means includes an asymmetrical silicon-controlled-rectifier, and a diode connected in antiparallel therewith.

52. The converter of claim 49 wherein each of said first and second input switching means includes a switching transistor, and a diode connected in antiparallel therewith.

53. The converter of claim 49 wherein each of said first and second output switching means includes a pair of blocking silicon-controlled-rectifiers connecting in antiparallel.

54. The converter of claim 49 wherein each of said first and second output switching means includes a switching transistor, and a diode converted in antiparallel therewith.

55. The converter of claim 49 wherein each of said first and second input switching means includes a pair of switching transistors connected in antiparallel.

56. The converter of claim 49 wherein each of said first and second output switching means includes a pair of switching transistors connected in antiparallel.