Patent ID: 7843082

Claim:
An islanding detection method for a distributed generation power system, comprising the steps of: a utility power system connecting with the distributed generation power system, the distributed generation power system including a power converter to connect with the utility power system; and controlling the power converter of the distributed generation power system to adopt a current-mode control, to have an output current tracing a reference signal including a real-power control signal and a virtual-capacitor control signal, and to act as a virtual capacitor at a frequency close to but unequal to a fundamental frequency of the utility power system for detecting islanding phenomenon under abnormal conditions of the utility power system; wherein when power failure occurs in the utility power system, only the distributed generation power system supplies power to a load such that the virtual capacitor of the power converter is enabled, thereby causing a significant change of a load voltage in at least one of amplitudes and frequencies; wherein the step of controlling the power converter to adopt the current-mode control, to have the output current tracing the reference signal including the real-power control signal and the virtual-capacitor control signal, and to act as the virtual capacitor comprises: detecting the load voltage by a voltage detector; filtering the load voltage by a first band-pass-filter having a center frequency the same with a fundamental frequency of the utility power system, so that an output of the first band-pass-filter is a sine-wave signal with a frequency and a phase identical with a frequency and a phase of a voltage of the utility power system; multiplying the output of the first band-pass-filter by an amplitude signal in a multiplier to obtain the real-power control signal; subtracting the output of the first band-pass-filter from the load voltage detected by the voltage detector by a first subtracter and sending the result of the first subtracter to a second band-pass-filter having a center frequency higher than the fundamental frequency of the utility power system; sending an output of the second band-pass-filter to a differentiator to generate the virtual-capacitor control signal; adding the real-power control signal and the virtual-capacitor control signal by an adder to obtain the reference signal; detecting an output current of the power converter by a current detector; subtracting the output current of the power converter from the reference signal by a second subtracter and sending an output of the second subtracter to a current controller; and sending an output of the current controller to a driving circuit to generate driving signals for power electronic switches of the power converter.