Method and system for selecting between centralized and distributed maximum power point tracking in an energy generating system

• US 20090284232A1
• Filed: 05/14/2008
• Published: 11/19/2009
• Est. Priority Date: 05/14/2008
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Lisi, Gianpaolo, Djabbari, Ali, Zhang, Jianhui
• Granted Patent: US 7,991,511 B2
• Time in Patent Office: Days
• US Class Current: 322/89
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02M 1/0077 Plural converter units whose outputs are connected in series
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 454/90 Ventilator using solar power

Abstract

A method for selecting between centralized and distributed maximum power point tracking in energy generating system is provided. The energy generating system includes a plurality of energy generating devices, each of which is coupled to a corresponding local converter. Each local converter includes a local controller for the corresponding energy generating device. The method includes determining whether the energy generating devices are operating under quasi-ideal conditions. The energy generating system is placed in a centralized maximum power point tracking (CMPPT) mode when the energy generating devices are operating under quasi-ideal conditions and is placed in a distributed maximum power point tracking (DMPPT) mode when the energy generating devices are not operating under quasi-ideal conditions.

Claims

1. A method for selecting between centralized and distributed maximum power point tracking in an energy generating system comprising a plurality of energy generating devices, each of the energy generating devices coupled to a corresponding local converter, each local converter comprising a local controller for the corresponding energy generating device, the method comprising:

determining whether the energy generating devices are operating under quasi-ideal conditions;

placing the energy generating system in a centralized maximum power point tracking (CMPPT) mode when the energy generating devices are operating under quasi-ideal conditions; and

placing the energy generating system in a distributed maximum power point tracking (DMPPT) mode when the energy generating devices are not operating under quasi-ideal conditions.

2. The method of claim 1, placing the system in the CMPPT mode comprising disabling the local controllers and enabling a global controller.

3. The method of claim 1, placing the system in the DMPPT mode comprising enabling the local controllers and disabling a global controller.

4. The method of claim 1, further comprising, when the system is in the DMPPT mode, determining whether a probability that at least one of the energy generating devices is shaded is above a predefined threshold.

5. The method of claim 4, further comprising, when the probability that at least one of the energy generating devices is shaded is determined to be above the predefined threshold:

identifying at least one potentially shaded energy generating device; and

performing a full characteristic scan for each identified potentially shaded energy generating device.

6. The method of claim 5, further comprising:

identifying at least one under-performing energy generating device based on the full characteristic scan; and

providing a correction to each identified under-performing energy generating device.

7. The method of claim 1, determining whether the energy generating devices are operating under quasi-ideal conditions comprising:

for each energy generating device, calculating a probability that the energy generating device is shaded based on output power values associated with each of the energy generating devices;

identifying a maximum value of the calculated probabilities;

comparing the maximum value of the calculated probabilities to a DMPPT threshold; and

determining that the energy generating devices are operating under quasi-ideal conditions when the maximum value of the calculated probabilities is less than the DMPPT threshold.

8. The method of claim 7, further comprising, when the system is in the DMPPT mode, comparing the maximum value of the calculated probabilities to a diagnostic threshold.

9. The method of claim 8, further comprising, when the maximum value of the calculated probabilities is greater than the diagnostic threshold, (i) identifying as a potentially shaded energy generating device each of the energy generating devices having a calculated probability that the energy generating device is shaded that is greater than the diagnostic threshold and (ii) performing a full characteristic scan for each identified potentially shaded energy generating device.

10. The method of claim 9, further comprising (i) identifying at least one under-performing energy generating device based on the full characteristic scan and (ii) providing a correction to each identified under-performing energy generating device.

11. The method of claim 1, the energy generating devices comprising photovoltaic panels.

12. A method for selecting between centralized and distributed maximum power point tracking in an energy generating system comprising a plurality of energy generating devices, each of the energy generating devices coupled to a corresponding local converter, each local converter comprising a local controller for the corresponding energy generating device, the method comprising:

calculating an output power value for each of the energy generating devices;

for each energy generating device, calculating a probability that the energy generating device is shaded based on the output power values for the energy generating devices;

identifying a maximum value of the calculated probabilities;

comparing the maximum value of the calculated probabilities to a distributed maximum power point tracking (DMPPT) threshold;

placing the energy generating system in a centralized maximum power point tracking (CMPPT) mode when the maximum value of the calculated probabilities is less than the DMPPT threshold; and

placing the energy generating system in a DMPPT mode when the maximum value of the calculated probabilities is equal to or greater than the DMPPT threshold.

13. The method of claim 12, further comprising, when the system is in the DMPPT mode, determining whether a probability that at least one of the energy generating devices is shaded is above a predefined threshold.

14. The method of claim 13, determining whether the probability that at least one of the energy generating devices is shaded is above the predefined threshold comprising comparing the maximum value of the calculated probabilities to a diagnostic threshold.

15. The method of claim 14, further comprising, when the maximum value of the calculated probabilities is greater than the diagnostic threshold, (i) identifying as a potentially shaded energy generating device each of the energy generating devices having a calculated probability that the energy generating device is shaded that is greater than the diagnostic threshold, (ii) performing a full characteristic scan for each identified potentially shaded energy generating device, (iii) identifying at least one under-performing energy generating device based on the full characteristic scan, and (iv) providing a correction to each identified under-performing energy generating device.

16. The method of claim 12, the energy generating devices comprising photovoltaic panels.

17. A central array controller capable of selecting between centralized and distributed maximum power point tracking for an energy generating system comprising a plurality of energy generating devices, each of the energy generating devices coupled to a corresponding local converter, each local converter comprising a local controller for the corresponding energy generating device, the central array controller comprising:

a diagnostic module capable of determining whether the energy generating devices are operating under quasi-ideal conditions; and

a control module capable of placing the energy generating system in a centralized maximum power point tracking (CMPPT) mode when the energy generating devices are operating under quasi-ideal conditions and placing the energy generating system in a distributed maximum power point tracking (DMPPT) mode when the energy generating devices are not operating under quasi-ideal conditions.

18. The central array controller of claim 17, the control module capable of placing the system in the CMPPT mode by disabling the local controllers and enabling a global controller.

19. The central array controller of claim 17, the control module capable of placing the system in the DMPPT mode by enabling the local controllers and disabling a global controller.

20. The central array controller of claim 17, the diagnostic module further capable of determining, when the system is in the DMPPT mode, whether a probability that at least one of the energy generating devices is shaded is above a predefined threshold.

21. The central array controller of claim 20, the diagnostic module further capable of, when the probability that at least one of the energy generating devices is shaded is determined to be above the predefined threshold, (i) identifying at least one potentially shaded energy generating device and (ii) performing a full characteristic scan for each identified potentially shaded energy generating device.

22. The central array controller of claim 21, the diagnostic module further capable of (i) identifying at least one under-performing energy generating device based on the full characteristic scan and (ii) providing a correction to each identified under-performing energy generating device.

23. The central array controller of claim 17, the energy generating devices comprising photovoltaic panels.