Voltage sag problems in large‐scale clustering wind farms

Accompanied by the development of large-scale wind energy and integration into grid in China, wind farm cascading trip-off accidents resulting from voltage sag have occurred frequently in the past few years. Before proposing countermeasures, it is necessary to clarify the voltage sag problem of wind farms. First, three voltage sag risk indices are proposed. Second, the simplified equivalent circuit of double fed induction generator (DFIG) for short-circuit calculation, stochastic model of wind speed and the fault model of buses/lines are presented in this paper. Third, assessment method of voltage sag in wind farm, implemented by Digsilent dynamic programming language (DPL), is proposed to analyze the severity and probability of voltage sag. Finally, a case study of wind farm connected to WSCC nine-bus benchmark systems is analyzed in detail, and the validity of the proposed approach is confirmed. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.