Research On The Anti-Islanding Method For Inverter-Based Distributed Generation

Distributed generation is an effective solution to reduce the distribution system losses and mitigate the greenhouse gas emission. With the popularity of the distributed generation, grid-connected inverters are increasingly employed for the renewable energy sources utilization. The inverter is an interface between the power system and the micro-grid, and it is equipped with islanding detection scheme. Islanding detection function is an integrant function for grid-connected inverters to avoid the damage of the equipment and to ensure the personal safety. Therefore, the impact of an inverter resident anti-islanding protection scheme is our new concern. The effect of islanding detection depends directly on the performance of islanding detection methods. Many anti-islanding protection schemes have been developed for inverter-based generators in recent years. In general, passive methods suffer from large non-detection zones. To avoid the large non-detection zones and to detect islanding in a timely manner, active islanding scheme are widely employed.The Sandia frequency shift (SFS) is selected as a representative of the positive feedback anti-islanding scheme in this paper. This paper investigates the influence of positive feedback anti-islanding scheme on inverter-based distributed generator stability. First, the adequate system model is established to represent the inverter anti-islanding actions. Second, On the basis of system model and the principle of the positive feedback anti-islanding scheme, the analytical small-signal model of distributed generator systems equipped with the positive feedback anti-islanding scheme is set up to determine the positive feedback gain and the stability limit. Third, The maximum output power limit versus positive feedback gain curve is proposed as an index for the stability analysis.Sensitivity studies of important parameters are conducted for DGs. the analytical model of distributed generator systems equipped with the positive feedback anti-islanding scheme is set up in the simulation environment of MATLAB/Simulink. Finally, the simulation results verify the theoretical analysis. The results show that the positive feedback anti-islanding scheme does have the potential to destabilize the DG system. If the positive feedback gain is too high, the DG system will become unstable.