Impact of Nonlinearity on Type-3 WT's Fault Current

Due to Type-3 wind turbine (WT) has already become a highly penetrated power source in modern power systems, characterizing its properties during short circuit is a basic requirement for system analysis. However, although nonlinearity, such as saturation effect of doubly fed induction generator (DFIG) and the dynamic of phase-locked loop (PLL), is a critical determinant, it has been simply ignored in the existing literatures. This paper is focusing on the impact of nonlinearity on Type-3 WT's fault current. First, a 10kW experimental prototype is carefully designed in laboratorial scale to demonstrate the dynamic performance of Type-3 WT during low voltage ride through (LVRT). Then, the impact of those nonlinear elements on fault current is quantified through the comparisons with the analytical results that are calculated without the consideration of nonlinearity. It shows that the nonlinear feature mainly influences the maximum value of fault current in the instant control time scale. Hence, expressions and method are proposed to evaluate the actual momentary current of a Type-3 WT. The conclusion of this paper is expected to be implemented in rating circuit breakers and other equipment.