System and method for over-voltage protection in a photovoltaic system

• US 8,884,465 B2
• Filed: 04/16/2010
• Issued: 11/11/2014
• Est. Priority Date: 04/17/2009
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Sarhan, Sameh
• Primary Examiner(s): Fureman, Jared
• Assistant Examiner(s): Mourad, Rasem
• Application Number:
  US12/762,134
• Publication Number:
  US 20100269883A1
• Time in Patent Office: 1,670 Days
• Field of Search: 361/15, 361/58, 307/66, 307/71, 307/77, 307/82
• US Class Current: 307/82
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers

Abstract

A photovoltaic array for use in an electrical power system includes multiple photovoltaic modules and a voltage converter coupled to at least one of the photovoltaic modules. The photovoltaic array also includes an over-voltage protection circuit. The over-voltage protection circuit includes an interface adapted to couple to an output of the voltage converter. The over-voltage protection circuit also includes a spike detector configured to detect a voltage spike in an output voltage of the voltage converter. The over-voltage protection circuit further includes a voltage control module configured to regulate an output voltage slew rate of the voltage converter in response to an over-voltage signal received from the spike detector.

Claims

1. A photovoltaic array for use in an electrical power system, the photovoltaic array comprising:

at least one string of multiple photovoltaic modules connected in series;

an inverter configured to couple power from the string of modules to a load;

at least one of the multiple modules having an associated voltage converter and an associated over-voltage protection circuit;

the voltage converter configured to convert power output from the module to the string; and

the over-voltage protection circuit comprising;

a spike detector configured to detect a string over-voltage event based on a rate of change of the output voltage of the voltage converter (output voltage slew rate) exceeding a threshold value; and

a voltage control module configured to regulate the output voltage slew rate of the voltage converter in response to the string over-voltage event, thereby limiting the output voltage slew rate of the voltage converter to less than the threshold value.

2. The photovoltaic array as set forth in claim 1, wherein the spike detector includes:

an analog-to-digital converter configured to convert the output voltage of the voltage converter into a digital output voltage representation; and

a digital detection module configured to detect, in response to the digital output voltage representation, the string over-voltage event.

3. The photovoltaic array as set forth in claim 1, wherein the voltage converter includes the over-voltage protection circuit.

4. The photovoltaic array as set forth in claim 1, wherein the spike detector includes:

an amplifier with first and second inputs;

a first voltage input circuit coupled to the first input; and

a second voltage input circuit coupled to the second input;

the first and second voltage input circuits configured to establish the threshold value of the output voltage slew rate

wherein the amplifier is configured to signal the string over-voltage event in response to detecting a difference between a voltage from the first voltage input circuit and a voltage from the second voltage input circuit as indicating that the output voltage slew rate exceeds the threshold value.

5. The photovoltaic array as set forth in claim 4, wherein establishing the threshold value of the output voltage slew rate comprises cooperatively sizing respective capacitors in the first and second voltage input circuits.

6. The photovoltaic array as set forth in claim 4, further comprising:

a hysteresis circuit configured to hysteretically control signaling successive string over-voltage events.

7. The photovoltaic array as set forth in claim 1, wherein the voltage control module is configured to limit a duty cycle of the voltage converter.

8. A device for use in a solar cell power system including at least one string of multiple photovoltaic modules connected in series, and an inverter configured to couple power from the string of modules to a load, at least one module operable with the device, the device comprising:

a voltage converter coupled to the associated module, and configured to convert power output from the module to the string;

an over-voltage protection circuit coupled to the voltage converter comprising;

a spike detector configured to detect a string over-voltage event based on a rate of change of the output voltage of the voltage converter (output voltage slew rate) exceeding a threshold value; and

a voltage control module configured to regulate the output voltage slew rate of the voltage converter in response to the string over-voltage event, thereby limiting the output voltage slew rate of the voltage converter to less than the threshold value.

9. The device as set forth in claim 8, wherein the spike detector includes:

an analog-to-digital configured to convert the output voltage of the voltage converter into a digital output voltage representation; and

a digital detection module configured to detect, in response to the digital output voltage representation, the string over-voltage event.

10. The device as set forth in claim 8, wherein the spike detector includes:

an amplifier with first and second inputs;

a first voltage input circuit coupled to the first input; and

a second voltage input circuit coupled to the second input;

the first and second voltage input circuits configured to establish the threshold value of the output voltage slew rate

wherein the amplifier is configured to signal the string over-voltage event in response to detecting a difference between a voltage from the first voltage input circuit and a voltage from the second voltage input circuit as indicating that the output voltage slew rate exceeds the threshold value.

11. The device as set forth in claim 10, wherein establishing the threshold value of the output voltage slew rate comprises cooperatively sizing respective capacitors in the first and second voltage input circuits.

12. The device as set forth in claim 10, further comprising:

a hysteresis circuit configured to hysteretically control signaling successive string over-voltage events.

13. The device as set forth in claim 8, wherein the voltage control module is configured to limit a duty cycle of the voltage converter.

14. The device as set forth in claim 8, wherein the voltage converter includes the over-voltage protection circuit.

15. A method for string over-voltage avoidance in a photovoltaic array that includes at least one string of multiple photovoltaic modules connected in series, and that includes an inverter configured to couple power from the string to a load, each of the modules having an associated voltage converter configured to convert power output from the module to the string, the method at each module of the array comprising:

sensing an output voltage of the associated voltage converter;

detecting a string over-voltage event based on a rate of change of the output voltage of the voltage converter (output voltage slew rate) exceeding a threshold value; and

regulating the output voltage slew rate of the voltage converter in response to the detection of the string over-voltage event, thereby limiting the output voltage slew rate of the voltage converter to less than the threshold value.

16. The method set forth in claim 15, wherein sensing the output voltage of the voltage converter comprises:

converting analog measurements of the output voltage into digital signals representing the output voltage; and

sampling the digital signals at a specified sampling frequency.

17. The method as set forth in claim 15, wherein detecting the string over-voltage event comprises:

generating first and second voltages such that a difference between the first and

second voltages corresponds to the output voltage slew rate; and

signaling the string over-voltage event when the difference between the first and second voltages corresponds to the output voltage slew rate exceeding the threshold value.

18. The method as set forth in claim 15, further comprising:

hysteretically controlling signaling successive string over-voltage events.

19. The method as set forth in claim 15, wherein regulating the output voltage slew rate of the voltage converter comprises limiting a duty cycle of the voltage converter.