Equivalent Modeling Method for Wind Farm when Inner Failure Occurs

Wind energy, as a kind of green energy sources, has become more widely used. However, the regional and multiple wind farm cascading trip-off induced by the wind farm inner failure will cause serious impacts on the power grid. Previous studies have focused on external failures in wind farms, so it is necessary to find a way to analyze the transient characteristics of wind farms when inner failures occur. Based on the demagnetizing control of low voltage ride through(LVRT), the wind farm equivalent model is established according to the generator groups divided by the switching situation of Crowbar after the fault. First, by taking the influence of rotor side converter into consideration, stator flux during grid voltage dip is calculated by state equation, then the demagnetizing rotor current is obtained. Using the demagnetizing rotor current, switching situation of Crowbar can be determined. Thereby the generators of the wind farm are divided into three groups. After analyzing the characteristics of wind farm inner failure, a novel method been proposed. The collector network does not need to be changed, but connection points of equivalent generators are determined by using the nonlinear programming. Finally, the example and simulation show that the method proposed can accurately reflect the characteristics of the wind farm before and after the failure.