CENTRALIZED MPPT EXITING AND SWITCHING METHOD AND APPLICATION THEREOF

• US 20170264099A1
• Filed: 07/15/2014
• Published: 09/14/2017
• Est. Priority Date: 07/15/2014
• Status: Active Grant

• Current Assignee: Sungrow Power Supply Co., Ltd.
• Original Assignee: Sungrow Power Supply Co., Ltd.
• Inventors: ZHANG, Fenggang, NI, Hua, ZHENG, Qun, ZHANG, Yanhu, HU, Bing
• Granted Patent: US 10,693,297 B2
• Time in Patent Office: Days
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2300/26 involving maximum power point tracking control for photovoltaic sources maximum power point systems in particular G05F1/67
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02J 3/381 Dispersed generators
• CPC Class Codes: H02M 7/44 by static converters
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

Disclosed is a centralized MPPT exiting method for a photovoltaic inverter comprising multiple DC chopper circuits and one inverter circuit. The method comprises: when the photovoltaic inverter is in a centralized MPPT mode, MPPT control is implemented independently for each photovoltaic cell in a photovoltaic component and the maximum power point for each photovoltaic cell is obtained; a reference value of the maximum power point for each photovoltaic cell is determined according to the type of the multiple DC chopper circuits; whether the voltage difference between the other maximum power points and the reference value goes beyond an allowable voltage difference is judged and the operation of the DC chopper circuits connecting to the photovoltaic cells with a voltage difference beyond the allowable voltage difference is recovered.

Claims

1. A method for exiting a MPPT centralized mode of a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the method comprising:

performing a MPPT control individually on each of photovoltaic strings to obtain a maximum power point for each of the photovoltaic strings, when the photovoltaic inverter is operating in the MPPT centralized mode, wherein the photovoltaic strings are connected in parallel to the DC bus via DC chopper circuits which stop operating;

determining a standard value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits; and

determining whether voltage differences between voltages of the maximum power points and the standard value exceed a preset voltage difference, and restarting DC chopper circuits connected to photovoltaic strings with voltage differences exceeding the preset voltage difference.

2. The method for exiting a MPPT centralized mode according to claim 1, wherein, before performing a MPPT control individually on each of photovoltaic strings, the method further comprises:

determining whether a voltage of the DC bus meets an inversion requirement and exiting the MPPT centralized mode if the voltage of the DC bus does not meet the inversion requirement.

3. The method for exiting a MPPT centralized mode according to claim 1, wherein, if the DC chopper circuits are boost chopper circuits, determining a standard value for the maximum power points of the photovoltaic strings comprises:

determining a maximum voltage among the voltages of the maximum power points of the photovoltaic strings.

4. The method for exiting a MPPT centralized mode according to claim 1, wherein, if the DC chopper circuits are buck chopper circuits, determining a standard value for the maximum power points of the photovoltaic strings comprises:

determining a minimum voltage among the voltages of the maximum power points of the photovoltaic strings.

5. A method for switching MPPT centralized modes of a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the method comprising a method for entering a MPPT centralized mode and the method for exiting the MPPT centralized mode according to claim 1, wherein the method for entering a MPPT centralized mode comprises:

obtaining a maximum power point for each of photovoltaic strings connecting to the plurality of DC chopper circuits;

determining a reference value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits;

suspending a DC chopper circuit connected with a photovoltaic string corresponding to the reference value; and

determining whether voltage differences between voltages of the maximum power points and the reference value exceed a preset voltage difference, and suspending DC chopper circuits connected to photovoltaic strings with voltage differences not exceeding the preset voltage difference.

6. The method for exiting a MPPT centralized mode according to claim 5, wherein, before obtaining a maximum power point for each of photovoltaic strings connected to the plurality of DC chopper circuits, the method further comprises:

determining whether a voltage of the bus meets an inversion requirement.

11. The method for exiting a MPPT centralized mode according to claim 2, wherein, if the DC chopper circuits are boost chopper circuits, determining a standard value for the maximum power points of the photovoltaic strings comprises:

determining a maximum voltage among the voltages of the maximum power points of the photovoltaic strings.

12. The method for exiting a MPPT centralized mode according to claim 2, wherein, if the DC chopper circuits are buck chopper circuits, determining a standard value for the maximum power points of the photovoltaic strings comprises:

determining a minimum voltage among the voltages of the maximum power points of the photovoltaic strings.

13. A method for switching MPPT centralized modes of a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the method comprising a method for entering a MPPT centralized mode and the method for exiting the MPPT centralized mode according to claim 2, wherein the method for entering a MPPT centralized mode comprises:

obtaining a maximum power point for each of photovoltaic strings connecting to the plurality of DC chopper circuits;

determining a reference value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits;

suspending a DC chopper circuit connected with a photovoltaic string corresponding to the reference value; and

determining whether voltage differences between voltages of the maximum power points and the reference value exceed a preset voltage difference, and suspending DC chopper circuits connected to photovoltaic strings with voltage differences not exceeding the preset voltage difference.

14. The method for exiting a MPPT centralized mode according to claim 13, wherein, before obtaining a maximum power point for each of photovoltaic strings connected to the plurality of DC chopper circuits, the method further comprises:

determining whether a voltage of the bus meets an inversion requirement.

15. A method for switching MPPT centralized modes of a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the method comprising a method for entering a MPPT centralized mode and the method for exiting the MPPT centralized mode according to claim 3, wherein the method for entering a MPPT centralized mode comprises:

obtaining a maximum power point for each of photovoltaic strings connecting to the plurality of DC chopper circuits;

determining a reference value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits;

suspending a DC chopper circuit connected with a photovoltaic string corresponding to the reference value; and

determining whether voltage differences between voltages of the maximum power points and the reference value exceed a preset voltage difference, and suspending DC chopper circuits connected to photovoltaic strings with voltage differences not exceeding the preset voltage difference.

16. The method for exiting a MPPT centralized mode according to claim 15, wherein, before obtaining a maximum power point for each of photovoltaic strings connected to the plurality of DC chopper circuits, the method further comprises:

determining whether a voltage of the bus meets an inversion requirement.

17. A method for switching MPPT centralized modes of a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the method comprising a method for entering a MPPT centralized mode and the method for exiting the MPPT centralized mode according to claim 4, wherein the method for entering a MPPT centralized mode comprises:

obtaining a maximum power point for each of photovoltaic strings connecting to the plurality of DC chopper circuits;

determining a reference value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits;

suspending a DC chopper circuit connected with a photovoltaic string corresponding to the reference value; and

determining whether voltage differences between voltages of the maximum power points and the reference value exceed a preset voltage difference, and suspending DC chopper circuits connected to photovoltaic strings with voltage differences not exceeding the preset voltage difference.

18. The method for exiting a MPPT centralized mode according to claim 17, wherein, before obtaining a maximum power point for each of photovoltaic strings connected to the plurality of DC chopper circuits, the method further comprises:

determining whether a voltage of the bus meets an inversion requirement.

19. A method for switching MPPT centralized modes of a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the method comprising a method for entering a MPPT centralized mode and the method for exiting the MPPT centralized mode according to claim 11, wherein the method for entering a MPPT centralized mode comprises:

obtaining a maximum power point for each of photovoltaic strings connecting to the plurality of DC chopper circuits;

determining a reference value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits;

suspending a DC chopper circuit connected with a photovoltaic string corresponding to the reference value; and

determining whether voltage differences between voltages of the maximum power points and the reference value exceed a preset voltage difference, and suspending DC chopper circuits connected to photovoltaic strings with voltage differences not exceeding the preset voltage difference.

20. A method for switching MPPT centralized modes of a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the method comprising a method for entering a MPPT centralized mode and the method for exiting the MPPT centralized mode according to claim 12, wherein the method for entering a MPPT centralized mode comprises:

obtaining a maximum power point for each of photovoltaic strings connecting to the plurality of DC chopper circuits;

determining a reference value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits;

suspending a DC chopper circuit connected with a photovoltaic string corresponding to the reference value; and

determining whether voltage differences between voltages of the maximum power points and the reference value exceed a preset voltage difference, and suspending DC chopper circuits connected to photovoltaic strings with voltage differences not exceeding the preset voltage difference.

7. An apparatus for exiting a MPPT centralized mode of a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the apparatus comprising:

a maximum power point determination unit, configured to perform a MPPT control individually on each of photovoltaic strings to obtain a maximum power point for each of the photovoltaic strings when the photovoltaic inverter is operating in the MPPT centralized mode, wherein the photovoltaic strings are connected in parallel to the DC bus via DC chopper circuits which stop operating;

a standard value determination unit connected with the maximum power point determination unit, configured to determine a standard value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits; and

a circuit restarting unit connected with the standard value determination unit, configured to determine whether voltage differences between voltages of the maximum power points and the standard value exceed a preset voltage difference, and restart DC chopper circuits connected to photovoltaic strings with voltage differences exceeding the preset voltage difference.

8. The apparatus for exiting a MPPT centralized mode according to claim 7, further comprising:

a bus voltage determination unit connected with the maximum power point determination unit, configured to determine whether a voltage of the DC bus meets an inversion requirement and exit the MPPT centralized mode if the voltage of the DC bus does not meet the inversion requirement.

9. An inverter control system for a photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, wherein, the control system is configured to, when the photovoltaic inverter is operating in a MPPT centralized mode, perform a MPPT control individually on each of photovoltaic strings to obtain a maximum power point for each of the photovoltaic strings, wherein the photovoltaic strings are connected in parallel to the DC bus via DC chopper circuits which stop operating;

determine a standard value for the maximum power points of the photovoltaic strings according to the type of the plurality of DC chopper circuits; and

determine whether voltage differences between voltages of the maximum power points and the standard value exceed a preset voltage difference, and restart DC chopper circuits connected to photovoltaic strings with voltage differences exceeding the preset voltage difference.

10. A photovoltaic inverter, wherein the photovoltaic inverter comprises a plurality of DC chopper circuits and an inverting circuit, and the inverting circuit is connected to an output side of the plurality of DC chopper circuits on which side the plurality of DC chopper circuits are connected in parallel to a DC bus, the photovoltaic inverter further comprising:

the inverter control system according to claim 9.