Method and apparatus for reactive power capable inverters

• US 9,450,405 B2
• Filed: 02/25/2014
• Issued: 09/20/2016
• Est. Priority Date: 02/25/2013
• Status: Active Grant

• Current Assignee: Enphase Energy Incorporated
• Original Assignee: Enphase Energy Incorporated
• Inventors: Fornage, Martin
• Primary Examiner(s): Deberadinis, Robert
• Application Number:
  US14/189,813
• Publication Number:
  US 20140239726A1
• Time in Patent Office: 938 Days
• Field of Search: 307/31
• US Class Current: 1/1
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources
• CPC Class Codes: H02J 3/00 Circuit arrangements for ac mains or ac distribution networks
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/46 Controlling of the sharing of output between the generators, converters, or transformers
• CPC Class Codes: H02M 7/53875 with analogue control of three-phase output
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A system, method, and apparatus for converting DC input power to AC output power, including a DC-AC inverter employing: a first feedback loop for determining a maximum power point (MPP) and operating the DC-AC inverter proximate the MPP. A second feedback loop for determining a difference between a first power measurement and a second power measurement, producing an error signal indicative of the difference, and coupling the error signal to the first feedback loop to adjust at least one operating parameter of the DC-AC inverter to drive toward the MPP, where the first power measurement and the second power measurement are each determined based on a phase shift between an AC output voltage from the DC-AC inverter and an AC output current from the DC-AC inverter.

Claims

1. An apparatus for converting DC input power to AC output power, comprising:

a DC-AC inverter employing;

a first feedback loop for determining a maximum power point (MPP) and operating the DC-AC inverter proximate the MPP; and

a second feedback loop for determining a difference between a first power measurement and a second power measurement, producing an error signal indicative of the difference, and coupling the error signal to the first feedback loop to adjust at least one operating parameter of the DC-AC inverter to drive toward the MPP, wherein the first power measurement and the second power measurement are each determined based on a phase shift between an AC output voltage from the DC-AC inverter and an AC output current from the DC-AC inverter.

2. The apparatus of claim 1, further comprising a burst mode controller for operating the DC-AC inverter in a burst mode when the DC input power is below a burst mode threshold, wherein during the burst mode (i) energy is stored in a storage capacitor of the DC-AC inverter during a storage period, and (ii) the energy is subsequently drawn from the storage capacitor during a burst period.

3. The apparatus of claim 1, wherein the first power measurement measures the DC input power during a first phase range of at least one cycle of an AC line coupled to an output from the DC-AC inverter and the second power measurement measures the DC input power during a second phase range of the at least one cycle.

4. The apparatus of claim 3, wherein the first phase range and the second phase range are of equal length and the first phase range and the second phase range are shifted with respect to zero-crossings of an AC voltage on the AC line by half of the phase shift.

5. The apparatus of claim 1, wherein the second feedback loop comprises an integrator for integrating the error signal.

6. The apparatus of claim 2, wherein the burst mode controller causes the AC output power to be greater than the DC input power during the burst period.

7. The apparatus of claim 2, wherein the AC output power is zero during the storage period.

8. A method for converting DC input power to AC output power, comprising:

determining via a first feedback loop of a DC-AC inverter, a maximum power point (MPP);

operating the DC-AC inverter proximate the MPP;

determining via a second feedback loop of the DC-AC inverter, a difference in a first power measurement and a second power measurement;

producing via the second feedback loop of the DC-AC inverter, an error signal indicative of the difference; and

adjusting via the first feedback loop and using the error signal, at least one operating parameter of the DC-AC inverter to drive toward the MPP, wherein the first power measurement and the second power measurement are each determined based on a phase shift between an AC output voltage from the DC-AC inverter and an AC output current from the DC-AC inverter.

9. The method of claim 8, further comprising operating the DC-AC inverter in a burst mode when the DC input power is below a burst mode threshold, wherein during the burst mode (i) energy is stored in a storage capacitor of the DC-AC inverter during a storage period, and (ii) the energy is subsequently drawn from the storage capacitor during a burst period.

10. The method of claim 8, wherein the first power measurement measures the DC input power during a first phase range of at least one cycle of an AC line coupled to an output from the DC-AC inverter and the second power measurement measures the DC input power during a second phase range of the at least one cycle.

11. The method of claim 10, wherein the first phase range and the second phase range are of equal length and the first phase range and the second phase range are shifted with respect to zero-crossings of an AC voltage on the AC line by half of the phase shift.

12. The method of claim 8, wherein the second feedback loop comprises an integrator for integrating the error signal.

13. The method of claim 9, wherein the AC output power is greater than the DC input power during the burst period.

14. The method of claim 9, wherein the AC output power is zero during the storage period.

15. The method of claim 8, further comprising measuring the DC input power during a first phase range of at least one cycle of a commercial power grid and measuring DC input power during a second phase range of the at least one cycle, wherein both ranges are shifted by the same phase.

16. A system for power conversion, comprising:

at least one photovoltaic (PV) module;

at least one DC-AC inverter, coupled to the at least one PV module, wherein each DC-AC inverter of the at least one DC-AC inverter employs;

a first feedback loop for determining a maximum power point (MPP) and operating the DC-AC inverter proximate the MPP; and

a second feedback loop for determining a difference between a first power measurement and a second power measurement, producing an error signal indicative of the difference, and coupling the error signal to the first feedback loop to adjust at least one operating parameter of the DC-AC inverter to drive toward the MPP, wherein the first power measurement and the second power measurement are each determined based on a phase shift between an AC output voltage from the DC-AC inverter and an AC output current from the DC-AC inverter.

17. The system of claim 16, further comprising operating each DC-AC inverter of the least one DC-AC inverter in a burst mode when DC input power is below a burst mode threshold, wherein during the burst mode (i) energy is stored in a storage capacitor of the DC-AC inverter during a storage period, and (ii) the energy is subsequently drawn from the storage capacitor during a burst period.

18. The system of claim 16, wherein the first power measurement measures DC input power during a first phase range of at least one cycle of an AC line coupled to an output from the DC-AC inverter and the second power measurement measures the DC input power during a second phase range of the at least one cycle.

19. The system of claim 18, wherein the first phase range and the second phase range are of equal length and the first phase range and the second phase range are shifted with respect to zero-crossings of an AC voltage on the AC line by half of the phase shift.

20. The system of claim 17, wherein the AC output power is zero during the storage period.