Improved voltage shift islanding detection method for multi-inverter grid-connected photovoltaic systems

This study presents an improved voltage shift islanding detection method with the new control mode. The proposed method adopts the modulation index shift scheme based on the pulse-width modulation control principle, which can promote the detection performance in the multi-inverter grid-connected photovoltaic (PV) systems, compared with the conventional voltage positive feedback (VPF) method. The superposition algorithm of the proposed method can make the rapid reduction of voltage magnitude at the point of common coupling during the islanding condition, and minimise the non-detection zone. Through the self-varying positive feedback gain, the synchronisation of voltage shift rates from multiple PV inverters can be effectively improved under the varying active power conditions. According to the characteristic of maximum power point tracking control, the gain will be automatically changed along with the variable PV voltage. The advantage of the proposed method is analysed by the simulation results in comparison with the conventional VPF method. Moreover, the experimental results are provided to verify the effectiveness of the proposed method.