Fault Current Analysis of Type-3 Wind Turbine Considering Dynamic Influence of Phase Locked Loop

As Type-3 wind turbine (WT)has already become a vital source in power system, analyzing its fault current is necessary. Although phase-angle jump of stator voltage always occurs during short circuit, it is neglected in existing research and the influence of phase locked loop (PLL)on fault current is still unclear. In this paper, an analytical model of Type-3 WT considering both magnitude drop and phase-angle jump is first developed. Then, the variable-frequency phenomenon of fault current component is discovered by comparing the results of modal analysis and Hilbert-Huang Transformation (HHT). Moreover, the dominant branch causing this phenomenon is extracted so that the whole system can be decomposed into a linear subsystem and a nonlinear subsystem. Based on these subsystems, an analytical expression of fault current is deduced and validated. The conclusion of this paper indicates that the variable-frequency phenomenon may result in protective relays' maloperation.