Boundary conditions of reactive-power-variation method and active-frequency-drift method for islanding detection of grid-connected photovoltaic inverters

Photovoltaic (PV) power conditioning system (PCS) has been increased around the world since PV is becoming widespread as a clean and gentle energy source for earth. As a result, high-density grid-connected PV PCS will be interconnected with distribution network. In this situation, islanding phenomenon becomes most important issues for the safety and stability. Many methods to prevent islanding phenomenon have been proposed and analyzed. Especially, active frequency drift positive feedback (AFDPF) method is to process output current waveform of PV PCS by chopping fraction. However, AFDPF method is not fully identified the chopping fraction considering output power quality and islanding prevention performance in IEEE Std 929-2000 islanding prevention test. In this paper the research for the minimum value of chopping fraction gain applied digital phase-locked-loop (DPLL) to AFDPF method considering output power quality and islanding prevention performance are performed by PSIM simulation and experiment in IEEE Std 929-2000 islanding prevention test.