active islanding detection method for the grid-connected photovoltaic generation system

this paper proposes an active islanding detection method incorporated into the control of the gridconnected inverter to protect the photovoltaic generation system from the islanding operation. the proposed active islanding detection method performs the grid-connected inverter as a virtual resistor with the operation frequency slightly higher or lower than the fundamental frequency of the utility voltage. the function of virtual resistor will not be actuated when the utility is nominal, and the gridconnected inverter can convert the dc power from the solar array to an ac power. when the strong utility is lost, the grid-connected inverter acts as a virtual resistor with the operation frequency slightly higher or lower than the fundamental frequency of the utility voltage. thus, the frequency and the amplitude of the local load voltage will be away from their normal values under the islanding operation. hence, the proposed active islanding detection method can immediately detect the islanding operation. a prototype is developed and tested to demonstrate the performance of the proposed active detection method. both computer simulation and experimental results verify that the performance of the proposed active islanding detection method is expected.