Methods and apparatus for controlling operation of photovoltaic power plants

• US 9,059,604 B2
• Filed: 06/27/2011
• Issued: 06/16/2015
• Est. Priority Date: 06/27/2011
• Status: Active Grant

• Current Assignee: Solaredge Technologies Incorporated
• Original Assignee: Sunpower Corporation (Totalenergies Se)
• Inventors: Johnson, Lars
• Primary Examiner(s): Barnie, Rexford
• Assistant Examiner(s): PARRIES, DRU M
• Application Number:
  US13/169,978
• Publication Number:
  US 20120326511A1
• Time in Patent Office: 1,450 Days
• Field of Search: 363/95, 307/51
• US Class Current: 1/1
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02J 3/50 Controlling the sharing of the out-of-phase component
• CPC Class Codes: H02S 10/00 PV power plants; Combinations of PV energy systems with other systems for the generation of electric power
• CPC Class Codes: H02S 50/00 Monitoring or testing of PV systems, e.g. load balancing or fault identification
• CPC Class Codes: H02S 50/10 Testing of PV devices, e.g. of PV modules or single PV cells testing of semiconductor devices during manufacturing H01L22/00
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A photovoltaic power plant includes a photovoltaic inverter that converts direct current generated by solar cells to alternating current. The output of the photovoltaic inverter is provided to a point of interconnection to a power grid. A meter at the point of interconnection may be read to detect the output of the photovoltaic inverter at the power grid. The photovoltaic power plant includes a plant controller with a state machine. The plant controller is configured to adjust setpoints of the photovoltaic inverter to control the output of the photovoltaic power plant. The plant controller is also configured to soft start and soft stop automatic voltage regulation (AVR) of the photovoltaic power plant to prevent perturbing the AVR.

Claims

1. A method of controlling a photovoltaic power plant, the method comprising:

generating direct current using a plurality of solar cells;

converting the direct current generated by the solar cells to alternating current using a photovoltaic inverter;

coupling an output of the photovoltaic inverter to a power grid;

detecting that the photovoltaic power plant generates a photovoltaic power plant output that exceeds a maximum allowable output limit of the photovoltaic power plant, the maximum allowable output limit being a maximum allowable reactive power or power factor of the photovoltaic power plant; and

in response to detecting that the photovoltaic power plant generates the photovoltaic power plant output that exceeds the maximum allowable output limit of the photovoltaic power plant, lowering a setpoint variable limit of the photovoltaic inverter from a first inverter setpoint limit to a second inverter setpoint limit to lower a limit on the reactive power output of the photovoltaic inverter.

2. The method of claim 1 wherein the photovoltaic power plant output comprises reactive power exported or absorbed by the photovoltaic inverter, the maximum allowable output limit of the photovoltaic power plant comprises a maximum allowable reactive power exported by the power plant, and each of the first and second inverter setpoint limits comprises a reactive power setpoint limit of the inverter.

3. The method of claim 1 wherein the detecting that the photovoltaic power plant generates the photovoltaic power plant output that exceeds the maximum allowable output limit of the photovoltaic power plant is performed in a first state of photovoltaic power plant operation and the lowering the setpoint variable limit of the photovoltaic inverter from the first inverter setpoint limit to the second inverter setpoint limit is performed in a second state of photovoltaic power plant operation.

4. The method of claim 3 further comprising, returning to the first state of photovoltaic power plant operation in response to detecting that the photovoltaic power plant output does not exceed the maximum allowable output limit of the photovoltaic power plant.

5. The method of claim 4 wherein the photovoltaic power plant is controlled by automatic voltage regulation (AVR) in the first state of photovoltaic power plant operation.

6. The method of claim 1 wherein the photovoltaic power plant output is detected at a point of interconnection (POI) to the power grid.

7. The method of claim 6 wherein the detecting that the photovoltaic power plant generates the photovoltaic power plant output that exceeds the maximum allowable output limit of the photovoltaic power plant is performed in a first state of photovoltaic power plant operation, and a third state of operation is entered when communications with a meter detecting the photovoltaic power plant output at the POI is lost.

8. The method of claim 1 wherein the photovoltaic power plant output comprises the power factor of the photovoltaic power plant, the maximum allowable output limit of the power plant comprises a maximum allowable power factor of the photovoltaic power plant, and each of the first and second inverter setpoint limits comprises a power factor setpoint limit of the inverter.

9. A photovoltaic power plant comprising:

a plurality of solar cells;

a photovoltaic inverter configured to convert direct current generated by the plurality of solar cells to alternating current;

a meter detecting an output of the photovoltaic power plant at a point of interconnection to a power grid; and

a plant controller comprising a state machine, the plant controller being configured to read the meter to detect the output of the photovoltaic power plant at the point of interconnection in a first state of operation and to dynamically adjust a setpoint variable limit of the photovoltaic inverter from a first inverter setpoint limit to a second inverter setpoint limit to lower a limit on the reactive power output of the photovoltaic inverter when the output of the photovoltaic power plant exceeds a maximum allowable output, the maximum allowable output being a maximum allowable reactive power or power factor of the photovoltaic power plant.

10. The photovoltaic power plant of claim 9 wherein the output of the photovoltaic power plant comprises reactive power and the setpoint variable limit comprises an inverter reactive power setpoint.

11. The photovoltaic power plant of claim 9 wherein the output of the photovoltaic power plant comprises power factor and the setpoint variable limit comprises an inverter power factor setpoint.

12. The photovoltaic power plant of claim 9 further comprising a compensator configured to receive and process readings from the meter.

13. The photovoltaic power plant of claim 12 wherein the compensator comprises a proportional-integral (PI) compensator.

14. The photovoltaic power plant of claim 9 wherein the photovoltaic power plant is controlled using automatic voltage regulation (AVR) in the first state of operation.

15. A photovoltaic power plant comprising:

a plurality of solar cells;

a photovoltaic inverter configured to convert direct current generated by the plurality of solar cells to alternating current;

a meter configured to detect an output of the photovoltaic power plant at a point of interconnection to a power grid; and

a plant controller configured to read the meter to detect a real power output of the photovoltaic power plant at the point of interconnection, to compare the real power output of the photovoltaic power plant to a minimum real power generation level, and to ramp down a reactive power setpoint of the photovoltaic inverter to unity power factor in response to detecting the real power output of the photovoltaic power plant to be below the minimum real power generation level.

16. The photovoltaic power plant of claim 15 wherein the plant controller is further configured to ramp up the reactive power setpoint of the photovoltaic inverter in response to detecting that the real power output of the photovoltaic power plant is above an enabling real power generation level.

17. The photovoltaic power plant of claim 16 further comprising a compensator configured to receive and process readings from the meter.

18. The photovoltaic power plant of claim 17 wherein the compensator comprises a proportional-integral (PI) compensator.