Microgrid Protection Criterion Based on Positive Sequence Component of Fault Current*

According to China's grid connection standard, the access of doubly-fed wind turbines of small and medium capacity causes the topology and operation mode of the distribution network, and the complexity and variability of the current level and direction of flow, which brings great challenges to the protection of microgrids. In this paper, based on the low-voltage ride-through operation characteristics of DFIG, the distribution characteristics of the positive sequence component of fault current in microgrids with doubly-fed turbines are analyzed in depth, and a longitudinal protection principle for microgrids based on the positive sequence component of fault current is proposed. This principle not only reduces the requirement of longitudinal protection on the data synchronization of communication equipment by using fault component amplitude transmission, but also eliminates the influence of load current and improves the action characteristics of protection. Finally, simulation is carried out by MATLAB/Simulink to verify the feasibility of the proposed protection principle.