ANTI-ISLANDING FOR GRID-TIE INVERTER USING COVARIANCE ESTIMATION AND LOGIC DECISION MAKER
First Claim
1. A method of anti-islanding a grid-connected distributed generation system from an electrical grid, comprising:
- introducing a first phase shift in an output current of an inverter of the distributed generation system;
calculating a covariance between the phase shift of the output current and a frequency of an output voltage of the inverter;
responsive to the covariance exceeding a predefined threshold, introducing a second phase shift larger than the first phase shift in the output current of the inverter;
detecting a deviation in the output voltage frequency responsive to introducing the second phase shift; and
responsive to the detecting, causing the inverter to disconnect from a load connected to the inverter.
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Accused Products
Abstract
An anti-islanding implementation that introduces a small, continuously varying phase shift pattern in the output current of an inverter. In grid-connected mode, this phase shift pattern has no impact on the frequency of the inverter'"'"'s output voltage. However, when islanded, the phase shift will cause the voltage frequency to deviate from nominal. Changes in the output current phase thus correlate well with the voltage frequency, so a covariance index is used to detect an islanding configuration. When this index exceeds a threshold, a larger phase shift pattern is introduced in the output current, large enough to cause the voltage frequency to fall outside the inverter'"'"'s trip protection window without compromising the inverter'"'"'s power quality yet ensuring reliable tripping of the inverter.
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Citations
20 Claims
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1. A method of anti-islanding a grid-connected distributed generation system from an electrical grid, comprising:
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introducing a first phase shift in an output current of an inverter of the distributed generation system; calculating a covariance between the phase shift of the output current and a frequency of an output voltage of the inverter; responsive to the covariance exceeding a predefined threshold, introducing a second phase shift larger than the first phase shift in the output current of the inverter; detecting a deviation in the output voltage frequency responsive to introducing the second phase shift; and responsive to the detecting, causing the inverter to disconnect from a load connected to the inverter. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of anti-islanding a grid-connected distributed generation system from an electrical grid, comprising:
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shifting, by a phase generator of a grid-tied inverter, the phase of an output current of the inverter of the distributed generation system by a first phase shift in the output current; calculating, by a controller, a correlation function that includes the first phase shift and a frequency of an output voltage of the inverter; responsive to an output of the correlation function exceeding a threshold, the phase generator shifting the phase of the output current by a second phase shift that is greater than the first phase shift; determining whether the output voltage frequency falls outside a frequency protection window of the inverter; and responsive to the output voltage frequency falling outside the frequency protection window, causing the inverter to interrupt the output current to a load connected to the inverter. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification