Anti-islanding accelerated by grid unbalance component

In this paper, a method to detect islanding operation of distributed generator (DG) is proposed, which exploits frequency drift accelerated by grid unbalance component, namely negative sequence component of grid voltage. The negative sequence component could be added to the gain of frequency feedback loop in the conventional anti-islanding scheme. To keep the power factor regulation, the displacement power factor (DPF) is considered in the tuning of feedback gain. The PLL (Phase-Locked Loop) with low bandwidth is used to replace the nominal frequency in calculating frequency deviation, and this brings the reduction of unnecessary reactive power injection during normal grid connected operation. The experimental results are shown to verify the effectiveness of the proposed method, which show that both detection time and NDZ (Non-Detection Zone) are improved. Also, the performance of the proposed method with multiple DG systems is discussed by introducing the equivalent single virtual inverter. The simulation and experimental results show validity of discussions.