Inverter ground fault circuit

• US 20060227472A1
• Filed: 07/22/2005
• Published: 10/12/2006
• Est. Priority Date: 04/07/2005
• Status: Abandoned Application

• Current Assignee: PV Powered, Inc. (Advanced Energy Industries, Inc. (China))
• Original Assignee: PV Powered, Inc. (Advanced Energy Industries, Inc. (China))
• Inventors: Taylor, William, Hoffman, Brian
• Application Number:
  US11/187,059
• Publication Number:
  US 20060227472A1
• Time in Patent Office: Days
• US Class Current: 361/42
• CPC Class Codes: H02H 3/04 with warning or supervision in addition to disconnection, e.g. for indicating that protective apparatus has functioned watching of pilot wires H02H1/0084; protection of protective arrangements H02H7/008; indication of the state of electronic switches H03K17/18
• CPC Class Codes: H02H 3/16 responsive to fault current to earth, frame or mass with balanced or differential arrangement H02H3/26 ; monitoring earth connection H02H5/105
• CPC Class Codes: H02H 7/1203 Circuits independent of the type of conversion

Abstract

A batteryless inverter allows for a positive or a negative lead from a photovoltaic array to be attached to a grounding terminal of the inverter. Internally a ground fault voltage is rectified and processed to produce a signal that will shut down the inverter. This signal will be the same whether the ground fault voltage is positive, negative, or AC.

Claims

1. A ground fault detection apparatus for use in an inverter connected to a photovoltaic panel comprising:

a ground conductor that connects a system ground in said inverter to earth ground;

a fuse device in series with said ground conductor;

a rectifier circuit connected in parallel with said fuse device;

a voltage detector that detects a rectified voltage across said fuse device; and

a switch that interrupts an electrical circuit within said inverter when a voltage is detected across said fuse device.

2. The ground fault detection apparatus of claim 1 wherein said fuse device is a fuse.

3. The ground fault detection apparatus of claim 1 wherein said fuse device is a circuit breaker.

4. The ground fault detection apparatus of claim 1 wherein said fuse device is a current sensor and a relay.

5. The ground fault detection apparatus of claim 1 wherein said fuse device is a relay.

6. The ground fault detection apparatus of claim 1 wherein said rectifier circuit produces a DC output with a predetermined voltage polarity regardless of the polarity of voltage across said fuse device and regardless of whether the voltage across said fuse device is AC or DC.

7. The ground fault detection apparatus of claim 6wherein said rectifier circuit comprises a plurality of diodes arranged to form a passive rectifier.

8. The ground fault detection apparatus of claim 7 wherein said rectifier circuit is an H bridge circuit.

9. The ground fault detection apparatus of claim 1 further comprising a signal conditioning circuit that converts said rectified voltage across said fuse to a signal in a different form that is appropriate for input to said voltage detector.

10. The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit comprises an opticoupler.

11. The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit comprises a low pass filter.

12. The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit comprises a Zener diode whereby said switch does not interrupt an electrical circuit within said inverter until said voltage across said fuse device exceeds a predetermined threshold level.

13. The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit comprises a transistor.

14. The ground fault detector apparatus of claim 9 wherein said signal conditioning circuit produces a binary signal with predetermined characteristics regardless of the magnitude and waveform of said rectified voltage across said fuse.

15. A solar generation system comprising:

a photovoltaic panel;

an inverter electrically connected to said photovoltaic panel for conditioning the output of said photovoltaic panel; and

a ground fault interrupter in said inverter comprising;

a ground conductor that connects a system ground to earth ground;

a fuse device in series with said ground conductor;

a voltage detector that detects a voltage across said fuse device; and

a switch that interrupts an electrical circuit within said inverter when a voltage is detected across said fuse device.

16. The solar generation system of claim 15 further comprising a rectifier circuit connected in parallel with said fuse device and wherein the voltage presented to said voltage detector has a polarity that is independent of the polarity and frequency of said voltage across said fuse device.

17. The ground fault detection apparatus of claim 16 wherein said rectifier circuit comprises a plurality of diodes arranged to form a passive rectifier.

18. The ground fault detection apparatus of claim 17 wherein said rectifier circuit is an H bridge circuit.

19. The ground fault detection apparatus of claim 16 further comprising a signal conditioning circuit that converts said rectified voltage across said fuse to a signal in a different form that is appropriate for input to said voltage detector.

20. The ground fault detector apparatus of claim 19 wherein said signal conditioning circuit produces a binary signal with predetermined characteristics regardless of the magnitude and waveform of said rectified voltage across said fuse.

21. A method of detecting a ground fault in an inverter comprising the steps of:

providing a system ground within said inverter;

providing a ground conductor between said system ground and earth ground;

providing a fuse device in series with said ground conductor that trips when electrical current in said ground conductor exceeds a predetermined level;

rectifying voltage across said fuse device whereby said rectified voltage is a DC voltage with a polarity that does not depend on the polarity of voltage across said fuse device and does not depend on whether voltage across said fuse device is AC or DC; and

detecting said rectified voltage across said fuse device as an indication of a ground fault condition.

22. The method of claim 21 further comprising the step of conditioning said rectified voltage.

23. The method of claim 22 wherein said step of conditioning said rectified voltage comprises the step of filtering high frequency electrical noise from said rectified voltage.

24. The method of claim 22 wherein said step of conditioning said rectified voltage comprises the step of blocking said voltage when it is less than a predetermined threshold value.

25. The method of claim 22 wherein said step of conditioning said rectified voltage comprises the step of optically isolating said voltage from a circuit that detects said voltage.

26. The method of claim 22 wherein said step of conditioning said rectified voltage comprises the step of converting said rectified voltage into a current signal with predetermined magnitude when said rectified voltage is above a predetermined threshold value.

27. The method of claim 21 further comprising the step of activating a switch to interrupt a circuit within said inverter when a ground fault condition is detected.