Method and system for providing local converters to provide maximum power point tracking in an energy generating system

• US 7,969,133 B2
• Filed: 05/14/2008
• Issued: 06/28/2011
• 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
• Primary Examiner(s): Berhane; Adolf
• Assistant Examiner(s): Tran; Nguyen
• Application Number:
  US12/152,491
• Publication Number:
  US 20090284240A1
• Time in Patent Office: 1,140 Days
• Field of Search: 323/222, 323/223, 323/224, 323/265, 323/266, 323/282, 323/283, 323/284, 323/285
• US Class Current: 323/283
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence

Abstract

A method for providing maximum power point tracking for an energy generating device using a local buck-boost converter coupled to the device is provided. The method includes operating in a tracking mode, which includes initializing a conversion ratio for the buck-boost converter based on a previous optimum conversion ratio. A device power associated with the initialized conversion ratio is calculated. The conversion ratio is repeatedly modified and a device power associated with each of the modified conversion ratios is calculated. A current optimum conversion ratio for the buck-boost converter is identified based on the calculated device powers. The current optimum conversion ratio corresponds to one of a buck mode, a boost mode and a buck-boost mode for the buck-boost converter.

Claims

1. A method for providing maximum power point tracking for an energy generating device using a local buck-boost converter coupled to the energy generating device, the method comprising operating in a tracking mode, wherein operating in the tracking mode comprises:

initializing a conversion ratio for the buck-boost converter based on a previous optimum conversion ratio;

calculating a device power associated with the initialized conversion ratio;

repeatedly modifying the conversion ratio and calculating a device power associated with each of the modified conversion ratios; and

identifying a current optimum conversion ratio for the buck-boost converter based on the calculated device powers, the current optimum conversion ratio corresponding to one of a buck mode, a boost mode and a buck-boost mode for the buck-boost converter.

2. The method of claim 1, further comprising storing the current optimum conversion ratio for the buck-boost converter.

3. The method of claim 1, further comprising operating in a dormant mode when a device voltage is less than a primary threshold voltage.

4. The method of claim 3, further comprising switching from the dormant mode to the tracking mode when the device voltage exceeds the primary threshold voltage.

5. The method of claim 4, further comprising reverting to the dormant mode from the tracking mode when the device voltage drops below a secondary threshold voltage, the secondary threshold voltage less than the primary threshold voltage.

6. The method of claim 1, further comprising, when the current optimum conversion ratio for the buck-boost converter is identified:

switching from the tracking mode to a holding mode for a specified period of time; and

reverting to the tracking mode from the holding mode after the specified period of time has passed.

7. The method of claim 1, further comprising, when the current optimum conversion ratio for the buck-boost converter is identified:

determining whether the current optimum conversion ratio corresponds to the buck-boost mode for the buck-boost converter;

when the current optimum conversion ratio corresponds to the buck-boost mode, switching from the tracking mode to a bypass mode for a first specified period of time and reverting to the tracking mode from the bypass mode after the first specified period of time has passed; and

when the current optimum conversion ratio does not correspond to the buck-boost mode, switching from the tracking mode to a holding mode for a second specified period of time and reverting to the tracking mode from the holding mode after the second specified period of time has passed.

8. The method of claim 1, the energy generating device comprising a photovoltaic panel.

9. A system for providing maximum power point tracking (MPPT) for each of a plurality of energy generating devices in an energy generating array, the system comprising, for each energy generating device:

a power stage configured to receive a device voltage and a device current from the energy generating device and to generate an output voltage and an output current based on the device voltage and the device current; and

a local converter comprising;

an MPPT module configured to operate in a tracking mode by (i) initializing a conversion ratio for the power stage based on a previous optimum conversion ratio, (ii) calculating a device power associated with the initialized conversion ratio, (iii) repeatedly modifying the conversion ratio and calculating a device power associated with each of the modified conversion ratios, and (iv) identifying a current optimum conversion ratio for the power stage based on the calculated device powers; and

a communication interface configured to provide information associated with the device voltage, device current, output voltage and output current to a central array controller for the array.

10. The system of claim 9, the MPPT module further configured to store the current optimum conversion ratio for the power stage.

11. The system of claim 9, the MPPT module further configured to operate in a dormant mode when the device voltage is less than a primary threshold voltage and to switch from the dormant mode to the tracking mode when the device voltage exceeds the primary threshold voltage.

12. The system of claim 11, the MPPT module further configured to revert to the dormant mode from the tracking mode when the device voltage drops below a secondary threshold voltage, the secondary threshold voltage less than the primary threshold voltage.

13. The system of claim 9, the MPPT module further configured to, when the current optimum conversion ratio for the power stage is identified:

switch from the tracking mode to a holding mode for a specified period of time; and

revert to the tracking mode from the holding mode after the specified period of time has passed.

14. The system of claim 9, wherein:

the current optimum conversion ratio corresponds to one of a buck mode, a boost mode and a buck-boost mode for the power stage; and

the MPPT module is further configured to, when the current optimum conversion ratio for the power stage is identified;

determine whether the current optimum conversion ratio corresponds to the buck-boost mode for the power stage;

when the current optimum conversion ratio corresponds to the buck-boost mode, switch from the tracking mode to a bypass mode for a first specified period of time and revert to the tracking mode from the bypass mode after the first specified period of time has passed; and

when the current optimum conversion ratio does not correspond to the buck-boost mode, switch from the tracking mode to a holding mode for a second specified period of time and revert to the tracking mode from the holding mode after the second specified period of time has passed.

15. The system of claim 9, the energy generating devices comprising photovoltaic panels.

16. A system for providing maximum power point tracking (MPPT) for each of a plurality of energy generating devices in an energy generating array, the system comprising, for each energy generating device:

a single-inductor, four-switch synchronous buck-boost switching regulator configured to receive a device voltage and a device current from the energy generating device and to generate an output voltage and an output current based on the device voltage and the device current; and

an MPPT module configured to receive the device voltage and the device current, the MPPT module comprising;

an MPPT control block configured to identify a current optimum conversion ratio based on the device voltage and the device current; and

a power stage regulator configured to select a mode for the switching regulator based on the current optimum conversion ratio and to operate the switching regulator in the selected mode;

wherein the MPPT control block is configured to identify the current optimum conversion ratio by operating in a tracking mode, which includes (i) initializing a conversion ratio for the switching regulator based on a previous optimum conversion ratio, (ii) calculating a device power associated with the initialized conversion ratio, (iii) repeatedly modifying the conversion ratio and calculating a device power associated with each of the modified conversion ratios, and (iv) identifying the current optimum conversion ratio for the switching regulator based on the calculated device powers.

17. The system of claim 16, wherein:

the power stage regulator comprises a buck-boost mode control logic and digital pulse width modulator;

the MPPT module further comprises a first analog-to-digital converter (ADC) configured to convert the device voltage from an analog device voltage to a digital device voltage and to convert the device current from an analog device current to a digital device current;

the MPPT control block is configured to identify the current optimum conversion ratio based on the digital device voltage and the digital device current; and

the power stage regulator is configured to operate the switching regulator in the selected mode by generating pulse width modulation signals for the switching regulator based on the current optimum conversion ratio.

18. The system of claim 17, wherein:

the MPPT module further comprises a second ADC configured to convert the output voltage from an analog output voltage to a digital output voltage and to convert the output current from an analog output current to a digital output current; and

the system further comprises a communication interface configured to provide information associated with the digital device voltage, the digital device current, the digital output voltage and the digital output current to a central array controller for the array.

19. The system of claim 16, the switching regulator comprising:

a first transistor and a second transistor coupled in series;

a third transistor and a fourth transistor coupled in series;

an inductor coupled to a first node between the first and second transistors and to a second node between the third and fourth transistors; and

a capacitor coupled in parallel with the third and fourth transistors.

20. The system of claim 19, the power stage regulator configured to:

(i) operate the switching regulator in a buck configuration by turning off the third transistor, turning on the fourth transistor, and alternately turning on the first and second transistors based on the current optimum conversion ratio;

(ii) operate the switching regulator in a boost configuration by turning on the first transistor, turning off the second transistor, and alternately turning on the third and fourth transistors based on the current optimum conversion ratio; and

(iii) operate the switching regulator alternately in the buck configuration and the boost configuration by performing time-division multiplexing between the buck configuration and the boost configuration based on the current optimum conversion ratio.

21. The system of claim 20, the power stage regulator further configured to:

(i) operate the switching regulator in a shutdown mode by turning off the first, second, third and fourth transistors; and

(ii) operate the switching regulator in a bypass mode by turning on the first and fourth transistors and turning off the second and third transistors.

22. The system of claim 16, the energy generating devices comprising photovoltaic panels.

23. The system of claim 16, wherein the MPPT control block is further configured to:

switch from the tracking mode to a holding mode for a specified period of time; and

revert to the tracking mode from the holding mode after the specified period of time has passed.

24. The system of claim 16, wherein the MPPT control block is further configured to:

determine whether the current optimum conversion ratio corresponds to the buck-boost mode for the buck-boost converter;

when the current optimum conversion ratio corresponds to the buck-boost mode, switch from the tracking mode to a bypass mode for a first specified period of time and revert to the tracking mode from the bypass mode after the first specified period of time has passed; and

when the current optimum conversion ratio does not correspond to the buck-boost mode, switch from the tracking mode to a holding mode for a second specified period of time and revert to the tracking mode from the holding mode after the second specified period of time has passed.