Hybrid islanding detection method by using grid impedance estimation in parallel-inverters-based microgrid

This paper presents a hybrid islanding detection algorithm integrated on the distributed generation unit more close to the point of common coupling of a Microgrid based on parallel inverters where one of them is responsible to control the system. The method is based on resonance excitation under grid impedance variation. Firstly, grid impedance variation will be detected easily and rapidly by sensing any abrupt grid current variation. Then, the closest inverter to the grid will excite the resonance to detect the grid fault by using virtual resistance, in order to extract the grid impedance parameters, both resistive and inductive parts, from the injected resonance frequency determination. Finally, the inverter will disconnect the microgrid from the faulty grid and reconnect the parallel inverter system to the controllable distributed system in order to ensure high power quality. This paper shows that grid impedance variation detection estimation can be an efficient method for islanding detection in microgrid systems. Theoretical analysis and simulation results are presented to validate the proposed method.