A New Adaptive Logic Phase-Shift Algorithm for Anti-Islanding Protections in Inverter-Based DG Systems

Recent developments in anti-islanding techniques have demonstrated that phase shift techniques are very effective for anti-islanding protections in inverter-based distributed generation (DG) systems. Several approaches have been proposed in the previous researches such as slide-mode frequency shift (SMS), active frequency drift (AFD), and active frequency drift with positive feedback (AFDPF) etc. The automatic phase shift (APS) method is actually a modified SMS method. It can effectively reduce the non-detection zone (NDZ) of the SMS technique by introducing an additional phase shift increment each time the frequency of the terminal voltage stabilizes. However, it is very difficult to determine a stable islanding frequency, and the APS algorithm sometimes acts slowly, even fails in certain load conditions. A new adaptive logic phase-shift (ALPS) algorithm is proposed in this paper to regulate the additional phase shift at a suspicious islanding situation and evaluate the effects of the phase shift. This algorithm can yield a quick phase shift in an islanding situation yet only produce a very small phase shift when the grid is available for inverter-based DG systems. Both simulation and experiment results have proved the robustness and effectiveness of the newly proposed anti-islanding algorithm