Accurate and Less-Disturbing Active Antiislanding Method Based on PLL for Grid-Connected Converters

An accurate and less-disturbing active antiislanding method suitable for grid-connected converters using phase-locked loop (PLL) based grid synchronization is proposed in this paper. The orthogonal signal generator required by a single-phase PLL is built using a second-order generalized integrator. The inverter current reference is slightly modified each output cycle by an injected signal, and a feedback signal is extracted fromthe voltage of the point of common coupling (PCC). When the grid becomes unavailable, the feedback signal moves outside of a preset threshold value. The disturbance caused by this method is small compared to other active antiislanding methods, such as active frequency drift or frequency shift up/down. The method does not affect the zero crossing of the injected current, can be used to estimate the grid impedance, and is highly robust to different grid disturbances and stiffness. The performance of the proposed method has been studied through extensive simulations using MATLAB/Simulink and experiments. Selected results are presented to confirm its validity.