Solar string power point optimization

• US 10,153,383 B2
• Filed: 03/12/2009
• Issued: 12/11/2018
• Est. Priority Date: 11/21/2008
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Foss, Andrew
• Primary Examiner(s): Leong, Susan D
• Assistant Examiner(s): Horton, Dujuan A
• Application Number:
  US12/403,339
• Publication Number:
  US 20100126550A1
• Time in Patent Office: 3,561 Days
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H01L 31/02021 for solar cells electrical connection means, e.g. junction boxes, specially adapted for structural association with photovoltaic modules H02S40/34
• CPC Class Codes: H02J 2300/24 of photovoltaic origin
• 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: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

An apparatus and method that controls the power produced by a string of solar cells, enabling the string to operate at its maximum power point when connected to a bus that operates at an externally controlled voltage. The apparatus and method can also be used to increase or decrease the output power of a string to any desired operating point.

Claims

1. A solar power generation system comprising:

at least one string of solar modules, the modules connected in series to a direct current (DC) bus;

each module to generate a module power output through the string to the DC bus, and to operate at a pre-defined module output power point when unimpaired; and

an injection circuit connected in series with the at least one string of modules, to selectively inject power into the string when one or more modules in the string generates an impaired module power output.

2. The system of claim 1, the injection circuit to inject power from one of:

(a) the DC bus, and (b) a power source external to the solar power generation system.

3. The system of claim 1, wherein impairment of module power output of a module results from a reduction in solar energy reaching that module caused by at least one of:

(a) shade, and (b) cloud cover.

4. The system of claim 1, the injection circuit including a power tracking unit to measure voltage across the string, and current through the string.

5. The system of claim 1, the injection circuit including a buck power converter circuit.

6. The system of claim 1, further comprising:

a direct current (DC) to alternating current (AC) inverter connected to the DC bus.

7. The system of claim 6, further comprising:

at least a second string of solar modules connected in series to the DC bus, and a corresponding second injection circuit connected in series with the second string of modules; and

a central control unit coupled to the inverter;

each injection circuit including a communication unit to communicate with the central control unit.

14. The system of claim 1, the injection circuit to selectively inject power into the string when one or more modules in the string generates an impaired module power output, such that each unimpaired module operates substantially at the associated pre-defined module output power point.

8. An apparatus for use in a solar power generation system including at least one string of solar modules connected in series to a direct current (DC) bus, each module operable to generate a module power output through the string to the DC bus, including a module power output at a pre-defined module output power point when unimpaired, the apparatus comprising:

a power injection unit connectable to the string of modules, in series with the modules, the injection unit including

detection circuitry to detect a string operating condition representative of module power output for modules in the string, including to detect an impairment condition indicating that at least one module in the string is generating an impaired module power output; and

injection circuitry to selectively inject power into the string when the detection circuitry detects the impairment condition.

9. The apparatus of claim 8, the injection circuitry to inject power from one of:

(a) the DC bus, and (b) a power source external to the solar power generation system.

10. The apparatus of claim 8, wherein impairment of module power output of a module results from a reduction in solar energy reaching that module caused by at least one of:

(a) shade, and (b) cloud cover.

11. The apparatus of claim 8, the detection circuitry to measure a string operating condition corresponding to voltage across the string, and current through the string.

12. The apparatus of claim 8, the injection circuitry including a buck converter circuit.

13. The apparatus of claim 8:

wherein the solar power generation system further comprises;

a direct current (DC) to alternating current (AC) inverter connected to the DC bus, and

a central control unit coupled to the inverter; and

wherein the injection circuitry includes a communication unit to communicate with the central control unit.

15. The apparatus of claim 8, the injection circuitry to selectively inject power into the string, such that each unimpaired module operates substantially at the associated pre-defined module output power point.

16. A method for controlling solar power generation in a solar power generation system including at least one string of solar modules connected in series to a direct current (DC) bus, each module operable to generate a module power output through the string to the DC bus, and to operate at a module output power point when unimpaired, the method comprising:

detecting a string operating condition representative of module power output for modules in the string, including a string operating condition in which each module is operating at a pre-defined module output power output point when unimpaired;

detecting an impairment condition indicating that at least one module in the string is generating an impaired module power output; and

when the impairment condition is detected, selectively injecting power into the string independent of the module power output for the modules in the string, by means of an injection circuit connected in series with the at least one string of modules.

17. The method of claim 16, wherein power is injected into the string when the impairment condition is detected such that each unimpaired module operates substantially at the associated pre-defined module output power point.

18. The method of claim 16, wherein power is injected into the string when the impairment condition is detected from one of:

(a) the DC bus, and (b) a power source external to the solar power generation system.

19. The method of claim 16 wherein detecting a string operating condition is based on at least one of voltage across the string, and current through the string.

20. The method of claim 16, wherein the solar power generation system includes a direct current (DC) to alternating current (AC) inverter connected to the DC bus, and a central control unit coupled to the inverter, the method further comprising:

communicating power injection status to the central control unit.