Abstract：Due to the large rotational inertia of synchronous machines，frequency changes caused by faults are

minimal. In contrast，new energy systems have smaller rotational inertia，which can result in more significant

frequency variations during faults. These larger frequency fluctuations inevitably lead to changes in the

characteristics of existing relay protection. There is limited research in the current literature on the frequency

variation characteristics of PMSG under fault conditions. To address this issue，firstly，analyzed the phase variation

characteristics of voltage and current during line faults based on a single direct-drive wind turbine system with an

infinite bus，considering the grid-side inverter control strategy，thus revealing the mechanism of frequency changes in PMSG. Then the impact of the phase lock error induced by the phase-locked loop on the frequency response characteristics of the direct-drive wind turbine was considered. Finally，through simulation，the effects of different fault types，fault durations，and short-circuit ratios on frequency variation characteristics were analyzed. Theoretical analysis and simulations show that the phase lead of voltage and current before the protection action is cumulative and effectively equivalent to an increase in frequency. The phase-locked loop error makes the frequency variation characteristics more complex，and different fault conditions result in different frequency variation characteristics.

      Key words：direct-drive wind turbines grid connection system；phase variation；frequency characteristics；

phase-locked loop error

     Format Citation:孙向飞，李平，达光军,等. 故障下直驱风机频率变化特性及其影响因素分析[J].电气传动,2026,56(06):49-57. SUN Xiangfei，LI Ping，DA Guangjun,et al. Analysis of frequency variation characteristics and influencing factors of PMSG under fault conditions [J].Electric Drive,2026,56(06):49-57