电网短路故障引发的全功率风电机组频率失稳机理与控制方法

Mechanism of Frequency Instability of Full-Scale Wind Turbines Caused by Grid Short Circuit Fault and Its Control Method

电网故障期间全功率风电机组由于持续的电流控制作用存在与电网频率异步、失稳的风险。为分析频率失稳机理,建立全功率风电机组并网系统的非线性降阶模型。由于该模型具有与同步机暂态稳定模型相似的结构特征,因此自然引入了"类机械转矩"和"类同步转矩"等概念,并利用等面积法揭示由暂态"转矩"不平衡所导致的全功率机组频率失稳这一内在机制。定量分析锁相环带宽、风机端口到故障点电气距离等因素对频率稳定裕度的影响,得出锁相环带宽越小,风机端口到故障点电气距离越近,越利于频率稳定等研究结论。提出一种有功、无功电流时序控制方法,在确保全功率机组频率稳定的同时,可以向电网提供无功电流支撑以满足并网导则要求。最后在PSCAD/EMTDC仿真平台上验证了分析结论的正确性与控制方法的有效性。

Full-scale wind turbines（FSWT） are susceptible to lose synchronization due to the continuous control interaction between FSWT and faulty grid. To reveal the mechanisms, a nonlinear reduced order model of FSWT was deducted based on its multi-time scale properties. Because the derived model has similar structural characteristics to the transient stability model of synchronous generator, the concepts of emulated mechanical torque and emulated synchronizing torque were introduced for better understanding. The mechanism of frequency instability of FSWT during grid faults was revealed by applying the principal of equal area. It is concluded that, the smaller the phase-locked loop（PLL） bandwidth is, the closer the distance from faulty point to FSWT terminal is, the larger the frequency stability margin is. Based on the mechanism, a time-sequence control of active and reactive current was proposed for frequency stabilization as well as grid reactive power support. Finally, time domain simulations in PSCAD/EMTDC prove the correctness of mechanism analysis and effectiveness of the proposed control strategy.