Granted Patent B2

US 7,945,413 · App. 11/849,827 · Granted May 17, 2011

Abstract

Claims (33)

1. A method for preventing islanding of a power source connected to an electric AC grid via an interface, the method comprising the steps of:

sensing an output voltage waveform of the interface using a high-pass filter circuit connected to an output of the interface;

generating a reference current waveform with the high-pass filter circuit, such that the reference current waveform is (i) proportional to the output voltage waveform and (ii) time delayed relative to the output voltage waveform;

controlling an output current waveform of the interface to track the reference current waveform; and

discontinuing said output current waveform when said output voltage waveform is sensed to be outside a predetermined waveform range.

2. The method of claim 1 , wherein the interface (i) comprises a power inverter or another form of a switching power converter, and (ii) controls the output current waveform flowing from the power source into the grid based on the reference current waveform.

3. The method of claim 1 , wherein said step of controlling said output current waveform comprises a step of tracking a maximum power point of the power source.

4. The method of claim 1 , wherein said step of discontinuing said output current waveform comprises turning off the power source and/or turning off the interface.

5. The method of claim 1 , wherein said step of discontinuing said output current waveform comprises disconnecting the power source from the AC electric grid.

6. The method of claim 1 , wherein said step of discontinuing said output current waveform is performed after said output voltage waveform is sensed to be outside of said predetermined waveform range for a predetermined number of line cycles of operation.

7. The method of claim 1 , wherein said step of sensing an output voltage waveform comprises sensing a frequency of said output voltage waveform.

8. The method of claim 1 , wherein said predetermined waveform range of said sensed voltage waveform includes a predetermined nominal value.

9. The method of claim 1 , wherein the power source comprises one or more sources.

10. A system for preventing islanding of a power source connected to an AC electric grid, comprising:

an interface connectable between the power source and the electric grid;

a sensor for sensing an output voltage waveform of said interface, the sensor comprising a high-pass filter circuit;

a control unit for controlling an output current waveform of said interface to track a reference current waveform having a mathematical relationship with the sensed output voltage waveform such that the output current waveform is proportional to an output of the high-pass filter circuit; and

a discontinuing unit for discontinuing said output current waveform when said output voltage waveform is sensed to be outside a predetermined waveform range.

11. The system of claim 10 , wherein said step of discontinuing said output current waveform is performed after said output voltage waveform is sensed to be outside of said predetermined waveform range for a predetermined number of line cycles of operation.

12. The system of claim 10 , wherein said mathematical relationship is a linear, nonlinear and/or non-invertible function of said sensed voltage waveform.

13. The system of claim 10 , wherein said mathematical relationship includes a time delay.

14. The system of claim 10 , wherein said mathematical relationship includes a small time variation.

15. A computer readable medium comprising instructions which when executed by a computer system causes the computer to implement a method for preventing islanding of a power source connected to an electric grid via an interface, the method comprising the steps of:

sensing an output voltage waveform of the interface;

controlling an output current waveform of the interface to track a reference current waveform having a mathematical relationship with the sensed output voltage waveform such that the output current waveform is (i) proportional to and (ii) time delayed relative to an output of a high-pass filter circuit connected to an output of the interface; and

discontinuing said output current waveform when said output voltage is sensed to be outside a predetermined voltage range.

16. A system for preventing islanding of a power source connected to an electric grid via an interface, the system comprising:

at least one processor programmed to (i) sense an output voltage of the interface and (ii) generate a reference current waveform that is proportional to a mathematical function of the output voltage, the mathematical function including a term proportion to the time derivative of the output voltage;

at least one processor programmed to control an output current waveform of the interface to track a reference current waveform; and

at least one processor programmed to discontinue said output current waveform when said output voltage waveform is sensed to be outside a predetermined waveform range.

17. The method of claim 1 , wherein sensing an output voltage waveform of the interface using a high-pass filter circuit comprises sensing an output voltage waveform of the interface using a high-pass capacitor-resistor (CR) filter circuit.

18. The system of claim 10 , wherein the high-pass filter circuit comprises a high-pass capacitor-resistor (CR) filter circuit.

19. The computer readable medium of claim 15 , wherein the output current waveform is (i) proportional to and (ii) time delayed relative to an output of a high-pass capacitor-resistor (CR) filter circuit connected to an output of the interface.

Assignments (9)