Power Factor Adjustment in Multi-Phase Power System

• US 20140306543A1
• Filed: 09/05/2013
• Published: 10/16/2014
• Est. Priority Date: 04/16/2013
• Status: Active Grant

• Current Assignee: SolarCity Corporation (Tesla Inc.)
• Original Assignee: Enecsys Limited
• Inventors: Garrity, Paul, Jungreis, Aaron M.
• Granted Patent: US 9,882,507 B2
• Time in Patent Office: Days
• US Class Current: 307/82
• CPC Class Codes: H02J 3/18 Arrangements for adjusting, eliminating or compensating reactive power in networks for adjustment of voltage H02J3/16
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02M 7/44 by static converters
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

A multi-phase power generation system for renewable energy, in which reactive elements (i.e., capacitors and/or inductors) can be selectively switched in and out in order to meet a particular power factor requirement, is provided. Each phase of the multi-phase power system receives generated powers from a set of inverters, and each phase has a set of switch reactive elements for making power factor adjustments to the power generated by the set of inverters. The power outputs of the set of inverters belonging to a particular phase are combined into a one combined ac power output, and the power factor adjustment for that particular phase is performed on the combined power output by the set of the switch reactive elements of that particular phase. In some embodiments, at least some of the inverters are micro-inverters that convert DC power from one or two solar panels to AC power.

Claims

1. A multi-phase power generation system comprising:

a plurality of sets of inverters for converting DC power into AC power;

a plurality of ac current combiners, each combiner for combining power outputs from one set of inverters from the plurality of sets of inverters into a combined ac power output for one phase of the multi-phase power generation system; and

a plurality of reactive power compensators, each reactive power compensator comprising a set of reactive elements, each reactive element switchable to be connected to said combined ac power output for performing power factor adjustment for one phase of the multi-phase power generation system.

2. The multi-phase power generation system of claim 1, wherein the set of reactive elements comprises a plurality of capacitors and a plurality of inductors.

3. The multi-phase power generation system of claim 1, wherein each inverter is a micro-inverter for converting DC power from photovoltaic (PV) cells from one solar panel.

4. The multi-phase power generation system of claim 1, wherein the inverters do not have switchable reactive elements.

5. The multi-phase power generation system of claim 1, wherein the inverters include switchable reactive elements for jointly performing the power factor adjustment.

6. The multi-phase power generation system of claim 1 further comprising a system controller for balancing the power output levels between the different phases.

7. The multi-phase power generation system of claim 6, wherein the power factor adjustment for a phase is based on the power output level of the phase after the system controller has balanced the power output levels between the different phases.

8. The multi-phase power generation system of claim 1, wherein the power factor adjustment for a phase is based on a power level ratio computed from a power output level of the phase relative to a rated maximum power output for the phase.

9. The multi-phase power generation system of claim 8, wherein the power output level of the phase is based on power output levels collected from inverters that produce ac power for the phase.

10. The multi-phase power generation system of claim 8, wherein the power factor adjustment is further based on a required power factor at the power level ratio.

11. The multi-phase power generation system of claim 10, wherein the power factor adjustment for the phase is further based on a difference between a displacement power factor of the phase and the required power factor at the power level ratio.

12. The multi-phase power generation system of claim 11, wherein the displacement power factor of the phase is based on a current measurement and a voltage measurement of the ac power being injected into an ac grid mains.

13. The multi-phase power generation system of claim 1, wherein each reactive power compensator of comprises a micro-controller for generating a set of switch drives for the set of reactive elements.

14. The multi-phase power generation system of claim 13, wherein the micro-controllers of the reactive power compensators are in a communications network with the plurality of sets of inverters.

15. The multi-phase power generation system of claim 14, wherein the communications network comprises a gateway controller for monitoring and controlling the multi-phase power generation system.

16. The multi-phase power generation system of claim 15, wherein the gateway controller is further for balancing the power levels of the different phases of the multi-phase power generation system.

17. A method of compensating reactive power by a multi-phase power generation system, the method comprising:

combining ac power outputs generated by a plurality of inverters for one phase of the multi-phase system into one combined ac power output for the phase;

receiving a current measurement and a voltage measurement for the combined ac power that is being injected into an grid mains; and

selecting a reactive element from a set of reactive element to be switched in in parallel with the combined ac output based on the current measurement and the voltage measurement.

18. The method of claim 17, wherein the set of reactive elements comprises a plurality of capacitors and a plurality of inductors.

19. The method of claim 17, wherein each inverter is a micro-inverter for converting DC power from photovoltaic (PV) cells from one solar panel.

20. The method of claim 17, wherein the inverters do not have switchable reactive elements.

21. The method of claim 17 further comprising balancing the power output levels between the different phases.

22. The method of claim 21, wherein the selecting of the reactive element is further based on the power output level of the phase after said balancing.

23. The method of claim 17, wherein the selecting of the reactive element comprises computing a power level ratio based on a power output level of the phase relative to a rated maximum power output for the phase.

24. The method of claim 23, wherein computing the power output level of the phase comprising collecting power output levels from inverters that produce the ac power for the phase.

25. The method of claim 23, wherein the selecting of the reactive element further comprises determining a required power factor at the computed power level ratio.

26. The method of claim 17, wherein the selecting of the reactive element comprises determining a difference between a displacement power factor of the phase and a required power factor, wherein the method further comprising computing the displacement power factor from the received current measurement and voltage measurement.