AC power supply apparatus and methods providing output control based on estimated instantaneous reactive power

• US 6,549,440 B2
• Filed: 07/19/2001
• Issued: 04/15/2003
• Est. Priority Date: 07/19/2001
• Status: Expired due to Term

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Powerware Corporation (Eaton Corporation PLC.)
• Inventors: Tassitino, Frederick Jr., Taimela, Pasi
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US09/908,990
• Publication Number:
  US 20030016548A1
• Time in Patent Office: 635 Days
• Field of Search: 363/71, 363/131, 323/205, 323/207, 307/52, 307/60, 307/82
• US Class Current: 363/131
• CPC Class Codes: H02J 9/062 for AC powered loads

Abstract

An AC power supply, e.g., an uninterruptible power supply (UPS), includes an output, a reference signal generator circuit operative to generate a reference signal representative of a desired voltage waveform at a node connected to the output, a power determiner circuit operative to generate an estimate of instantaneous reactive power transferred between the output and the node, and a reference signal compensator circuit responsive to the reference signal generator circuit and to the power determiner circuit and operative to generated a compensated reference signal from the reference signal responsive to the estimate of instantaneous reactive power. An AC voltage generator circuit is responsive to the reference signal compensator and operative to transfer current between the output and the node responsive to the compensated reference signal. For example, the AC voltage generator circuit may include a controlled inverter that includes an output voltage control loop that receives the compensate reference signal at a reference input thereof. Related methods are also described.

Claims

1. An AC power supply, comprising:

an output;

a reference signal generator circuit operative to generate a reference signal representative of a desired voltage waveform at a node connected to the output;

a power determiner circuit operative to generate an estimate of instantaneous reactive power transferred between the output and the node;

a reference signal compensator circuit operative to generate a compensated reference signal from the reference signal responsive to the estimate of instantaneous reactive power; and

an AC voltage generator circuit operative to transfer current between the output and the node responsive to the compensated reference signal.

2. A power supply according to claim 1, wherein the power determiner circuit is operative to generate the estimate of instantaneous reactive power from an estimate of instantaneous current and an estimate of instantaneous voltage at the output of the AC power supply.

3. A power supply according to claim 2:

wherein the reference signal comprises a first sinusoidal reference signal having a frequency and phase indicative of a frequency and phase of the desired voltage waveform at the node; and

wherein the power determiner circuit includes;

a first multiplier operative to multiply the sinusoidal reference signal by an estimate of voltage at the output of the AC power supply to produce a second sinusoidal reference signal that is representative of the instantaneous voltage;

a phase shifter circuit operative to process the second sinusoidal reference signal to produce a third sinusoidal reference signal that is quadrature phase shifted with respect to the second sinusoidal reference signal; and

a second multiplier operative to multiply the third sinusoidal reference signal by the estimate of instantaneous current to produce the estimate of instantaneous reactive power.

4. A power supply according to claim 1, wherein the reference signal compensator circuit is operative to generate the compensated reference signal by time-shifting and/or amplitude modulating the reference signal responsive to the estimate of instantaneous reactive power.

5. A power supply according to claim 4:

wherein the reference signal comprises a first periodic signal;

wherein the reference signal compensator circuit is operative to amplitude modulate the first periodic signal responsive to the estimate of instantaneous reactive power to generate a second periodic signal; and

wherein the AC voltage generator circuit is operative to control current transfer between the output and the node responsive to the second periodic signal.

6. A power supply according to claim 5:

wherein the power determiner circuit is further operative to generate an estimate of instantaneous real power transferred between the output and the node; and

wherein the reference signal generator circuit is operative to amplitude modulate the first periodic signal responsive to the estimate of instantaneous reactive power and the estimate of instantaneous real power.

7. A power supply according to claim 6, wherein the reference signal generator circuit is operative to amplitude modulate the first periodic reference signal responsive to the estimate of instantaneous real power when the estimate of instantaneous real power meets a first predetermined criterion, and wherein the reference signal generator circuit is operative to prevent amplitude modulation of the first periodic reference signal responsive to the estimate of instantaneous real power when the estimate of instantaneous real power meets a second predetermined criterion.

8. A power supply according to claim 5:

wherein the reference signal compensator circuit is operative to process an RMS voltage reference signal according the estimate of instantaneous reactive power to generate a compensated RMS voltage reference signal;

wherein the power supply further comprises;

an RMS voltage determiner circuit operative to generate an RMS voltage signal representative of an RMS voltage at the output;

a summing circuit that generates an RMS voltage error signal from the RMS voltage signal and the compensated RMS voltage reference signal; and

an RMS voltage compensation circuit operative to process the RMS voltage error signal according to a predetermined compensation to produce an RMS voltage compensation signal; and

wherein the reference signal compensator circuit is further operative to amplitude modulate the first periodic signal according to the RMS voltage compensation signal to produce the second periodic signal.

9. A power supply according to claim 8:

wherein the reference signal compensator circuit is operative to time shift and/or amplitude modulate the first periodic signal responsive to the estimate of instantaneous reactive power to generate a compensated periodic signal and to generate the compensated RMS voltage reference signal responsive to the compensated periodic signal; and

wherein the reference signal compensator circuit is operative to amplitude modulate the compensated periodic signal according to the RMS voltage compensation signal to produce the second periodic signal.

10. A power supply according to claim 4:

wherein the reference signal compensator circuit is operative to generate a first sinusoidal signal from the reference signal and to amplitude modulate the first sinusoidal signal responsive to the estimate of instantaneous reactive power to generate a second sinusoidal signal; and

wherein the AC voltage generator circuit is operative to control current transfer between the output and the node responsive to the second sinusoidal signal.

11. A power supply according to claim 10, wherein the first and second sinusoidal signals are digital approximations of continuous sinusoids.

12. A power supply according to claim 10, wherein the reference signal compensator circuit is further operative to time shift the first sinusoidal signal responsive to the estimate of instantaneous reactive power.

13. A power supply according to claim 12, wherein the reference signal compensator circuit is operative to time shift the first sinusoidal signal responsive to the estimate of instantaneous reactive power and to an estimate of instantaneous real power transferred between the output and the node.

14. A power supply according to claim 10:

wherein the reference signal comprises a first index signal;

wherein the reference signal compensator circuit comprises;

a first compensation circuit operative to process the estimate of instantaneous reactive power according to a first compensation to generate a first compensation signal;

a summing circuit operative to modify the first index signal responsive to the first compensation signal factor to produce a second index signal that is time-shifted with respect to the first index signal;

a sine lookup table circuit operative to generate the first sinusoidal signal responsive to the second index signal;

a second compensation circuit operative to process the estimate of instantaneous reactive power according to a second compensation to produce a second compensation signal; and

a multiplier circuit operative to amplitude modulate the first sinusoidal signal responsive to the second compensation signal to produce the second sinusoidal signal.

15. A power supply according to claim 14:

wherein the reference signal compensator circuit further comprises;

a third compensation circuit operative to process an estimate of instantaneous real power transferred between the output and the node according to a third compensation to produce a third compensation signal; and

a fourth compensation circuit operative to process the estimate of instantaneous real power according to a fourth compensation to produce a fourth compensation signal;

wherein the summing circuit is operative to modify the first index signal responsive to the first and third compensation signals to produce the second index signal; and

wherein the multiplier circuit is operative to amplitude modulate the first sinusoidal signal responsive to the second and fourth compensation signals to generate the second sinusoidal signal.

16. A power supply according to claim 1, wherein the AC voltage generator circuit comprises a controlled inverter.

17. A power supply according to claim 16, wherein the controlled inverter comprises an output voltage control loop that receives the compensate reference signal at a reference input thereof.

18. An AC power supply, comprising:

an output;

means for generating a reference signal representative of a desired voltage waveform at a node connected to the output;

means for generating a compensated reference signal from the reference signal responsive to an estimate of instantaneous reactive power transferred between the output and the node; and

means for controlling current transfer between a power source and the node via the output responsive to the compensated reference signal.

19. A power supply according to claim 18, further comprising means for generating the estimate of instantaneous reactive power from an estimate of instantaneous current and an estimate of instantaneous voltage at the output of the AC power supply.

20. A power supply according to claim 19:

wherein the reference signal comprises a first sinusoidal reference signal having a frequency and phase indicative of a frequency and phase of the desired voltage waveform at the node; and

wherein the means for generating the estimate of instantaneous reactive power from an estimate of instantaneous current and an estimate of instantaneous voltage comprises;

means for multiplying the sinusoidal reference signal by an estimate of voltage at the output to produce a second sinusoidal reference signal representative of the instantaneous voltage;

means for processing the second sinusoidal reference signal to produce a third sinusoidal reference signal that is quadrature phase shifted with respect to the second sinusoidal reference signal; and

means for multiplying the third sinusoidal reference signal by the estimate of instantaneous current to produce the estimate of instantaneous reactive power.

21. A power supply according to claim 18, wherein the means for generating a compensated reference signal comprises means for generated the compensated reference signal from the reference signal responsive to the estimate of instantaneous reactive power transferred between the output and the node and to an estimate of instantaneous real power transferred between the output and the node.

22. An uninterruptible power supply (UPS), comprising:

a DC voltage generating circuit configured to connect to an AC power source and to an auxiliary power source and operative to produce a DC voltage circuit at a DC bus from the AC power source and/or the auxiliary power source;

a controlled inverter coupled to the DC bus and operative to produce an AC voltage at an output thereof from the DC voltage on the DC bus responsive to a signal applied to a reference input of the controlled inverter;

a reference signal generator circuit operative to generate a reference signal representative of a desired voltage waveform at a node connected to the output of the controlled inverter;

a power determiner circuit operative to generate an estimate of instantaneous reactive power transferred between the output of the inverter and the node; and

a reference signal compensator circuit responsive to the reference signal generator circuit and to the power determiner circuit and operative to generate a compensated reference signal at the reference input of the controlled inverter from the reference signal responsive to the estimate of instantaneous reactive power.

23. A UPS according to claim 22, wherein the power determiner circuit is operative to generate the estimate of instantaneous reactive power from an estimate of instantaneous current and an estimate of instantaneous voltage at the output of the controlled inverter.

24. A UPS according to claim 22:

wherein the reference signal comprises a first sinusoidal reference signal having a frequency and phase indicative of a frequency and phase of the desired voltage waveform at the node; and

wherein the power determiner circuit includes;

a first multiplier operative to multiply the sinusoidal reference signal by an estimate of voltage at the output to produce a second sinusoidal reference signal representative of the instantaneous voltage;

a phase shifter circuit operative to process the second sinusoidal reference signal to produce a third sinusoidal reference signal that is quadrature phase shifted with respect to the second sinusoidal reference signal; and

a second multiplier operative to multiply the third sinusoidal reference signal by the estimate of instantaneous current to produce the estimate of instantaneous reactive power.

25. A UPS according to claim 22:

wherein the power determiner circuit is operative to generate an estimate of instantaneous real power transferred between the output of the inverter and the node; and

wherein the reference signal compensator circuit is operative to generate the compensated reference signal from the reference signal responsive to the estimate of instantaneous reactive power and to the estimate of instantaneous real power.

26. A method of operating an AC power supply, the method comprising:

generating a reference signal representative of a desired voltage waveform at a node connected to an output of the AC power supply;

modifying the reference signal responsive to an estimate of instantaneous reactive power transferred between the output and the node to generate a compensated reference signal; and

controlling current transfer between the output and the node responsive to the compensated reference signal.

27. A method according to claim 26, further comprising generating the estimate of instantaneous reactive power from an estimate of instantaneous current and an estimate of instantaneous voltage at the output of the AC power supply.

28. A method according to claim 27:

wherein the reference signal comprises a first sinusoidal reference signal having a frequency and phase indicative of a frequency and phase of the desired voltage waveform at the node; and

wherein generating the estimate of instantaneous reactive power from an estimate of instantaneous current and an estimate of instantaneous voltage comprises;

multiplying the sinusoidal reference signal by an estimate of a voltage at the output to produce a second sinusoidal reference signal representative of the instantaneous voltage;

processing the second sinusoidal reference signal to produce a third sinusoidal reference signal that is quadrature phase shifted with respect to the second sinusoidal reference signal; and

multiplying the third sinusoidal reference signal by the estimate of instantaneous current to produce the estimate of instantaneous reactive power.

29. A method according to claim 26, wherein modifying the reference signal comprises time-shifting and/or amplitude modulating the reference signal responsive to the estimate of instantaneous reactive power.

30. A method according to claim 29:

wherein the reference signal comprises a first periodic signal;

wherein time shifting and/or amplitude modulating the reference signal comprises amplitude modulating the first periodic signal responsive to the estimate of instantaneous reactive power to generate a second periodic signal; and

wherein controlling current transfer between the output and the node comprises controlling current transfer between the output and the node responsive to the second periodic signal.

31. A method according to claim 30, wherein amplitude modulating the first periodic signal comprises amplitude modulating the first periodic signal responsive to the estimate of instantaneous reactive power and an estimate of instantaneous real power transferred between the output and the node.

32. A method according to claim 31, further comprising preventing amplitude modulation of the first periodic signal responsive to the estimate of instantaneous real power when the estimate of instantaneous real power meets a predetermined criterion.

33. A method according to claim 30, wherein time shifting and/or amplitude modulating the reference signal comprises:

processing an RMS voltage reference signal according the estimate of instantaneous reactive power to generate a compensated RMS voltage reference signal;

summing an RMS voltage signal representative of an RMS voltage at the output and the compensated RMS voltage reference signal to generate an RMS voltage error signal;

processing the RMS voltage error signal according to a predetermined compensation to produce an RMS voltage compensation signal; and

amplitude modulating the first periodic signal according to the RMS voltage compensation signal to produce the second periodic signal.

34. A method according to claim 33, wherein time shifting and/or amplitude modulating the reference signal further comprises:

time shifting and/or amplitude modulating the first periodic signal responsive to the estimate of instantaneous reactive power to generate a compensated periodic signal;

generating the compensated RMS voltage reference signal responsive to the compensated periodic signal; and

amplitude modulating the compensated periodic signal according to the RMS voltage compensation signal to produce the second periodic signal.

35. A method according to claim 29:

wherein time shifting and/or amplitude modulating the reference signal comprises;

generating a first sinusoidal signal from the reference signal; and

amplitude modulating the first sinusoidal signal responsive to the estimate of instantaneous reactive power to generate a second sinusoidal signal; and

wherein controlling power transfer between the output and the node comprises controlling power transfer between the output and the node responsive to the second sinusoidal signal.

36. A method according to claim 35, wherein the first and second sinusoidal signals are digital approximations of continuous sinusoids.

37. A method according to claim 35, wherein generating a first sinusoidal signal comprises time-shifting the first sinusoidal signal responsive to the estimate of instantaneous reactive power.

38. A method according to claim 37, wherein generating a first sinusoidal signal comprises time-shifting the first sinusoidal signal responsive to the estimate of instantaneous reactive power and an estimate of instantaneous real power transferred between the output and the node.

39. A method according to claim 35:

wherein the reference signal comprises a first index signal, and wherein generating a first sinusoidal signal comprises;

processing the estimate of instantaneous reactive power according to a first compensation to generate a first compensation signal;

summing the first index signal and the first compensation signal to generate a second index signal that is time shifted with respect to the first index signal; and

processing the second index signal according to a sine lookup table to generate the first sinusoidal signal; and

wherein amplitude modulating the first sinusoidal signal comprises;

processing the estimate of instantaneous reactive power according to a second compensation to generate a second compensation signal; and

multiplying the first sinusoidal signal by the second compensation signal to generate the second sinusoidal signal.

40. A method according to claim 39:

wherein generating a first sinusoidal signal further comprises processing an estimate of real power transferred between the output and the node according to a third compensation to generate a third compensation signal;

wherein summing the first index signal and the first compensation signal comprises summing the first index signal, the first compensation signal and the second compensation signal to generate the second index signal;

wherein amplitude modulating the first sinusoidal signal further comprises processing the estimate of real power according to a fourth compensation to generate a fourth compensation factor; and

wherein multiplying the first sinusoidal signal comprises multiplying the first sinusoidal signals by the second and fourth compensation signals to generate the second sinusoidal signal.

41. A method according to claim 26, wherein the AC power supply comprises an uninterruptible power supply (UPS) configured to receive an AC input voltage and operative to generate an AC voltage at the output of the AC power supply therefrom, and wherein generating a reference signal comprises synchronizing the reference signal to the AC input voltage.

42. A method according to claim 26, wherein controlling current transfer between the output and the node comprises controlling an inverter having an output that is coupled to the node responsive to the compensated reference signal.

43. A method according to claim 42, wherein controlling an inverter comprises controlling a reference input of an inverter output voltage control loop responsive to the compensated reference signal.

44. A method according to claim 26, further comprising coupling the AC power supply to at least one other AC power supply and a load at the node.

45. A method according to claim 44, wherein the at least one other AC power supply comprises an AC utility source coupled to the node via a bypass circuit.