本文针对多端柔性直流输电的下垂控制方式,研究其工作特性和控制原理,推导其小信号模型,得到基于下垂控制的多端柔性直流输电系统(voltage soured converter based multi-terminal direct current, VSC-MTDC)小信号模型。在此基础上推导出下垂控制下换流站对交流系统的影响机理,并得到相关结论。最后在一个基于两区四机的三端直流网络系统中证明了本文模型及结论的正确性,即下垂控制对振荡传递的双向性,并得到下垂系数对系统稳定的影响机理。接着使用粒子群算法求解最优的下垂系数,对比仿真结果证明了其可行性和优越性。仿真结果还显示直流系统对低频振荡的隔离性,通过直流系统引起的受迫振荡幅度较小。
英文摘要:
This paper studies the working characteristics and control principles of DC droop control of VSC-MTDC (voltage soured converter based multi-terminal direct current) and deduce its small-signal model based on droop control strategy. On this basis, the impact mechanism of VSC station on AC system and relevant conclusions are derived. Finally, the correctness of the model and conclusions are validated in a three-terminal DC system based on 2A4M system and the impact of droop coefficient on system stability is revealed, i.e. the bidirectional characteristic to spread oscillations. Then the optimal droop coefficient is obtained based on PSO whose feasibility and superiority are demonstrated by comparative simulations. Simulation results also reveal the isolation of DC system to low frequency oscillations, the amplitude of forced oscillations caused through DC system is relatively small.