采用桥臂电抗投切控制的MMC降电容运行方法

Operation Method for MMC Capacitance Reduction with Arm Reactor Switching Control

随着柔性直流输电技术的发展,换流阀轻型化的需求日益迫切,对子模块电容电压纹波幅值的要求决定了电容值的降低比较困难,是影响换流阀轻型化的关键因素之一。根据基频、二倍频分量在子模块电容电压波动中占主导的特点,提出一种通过控制桥臂电抗值的方式降低子模块电容电压波动的策略。设计了桥臂电抗投切电路和投切控制策略,并从数学原理上对比分析了所提策略与现有环流抑制控制策略的不同之处与优势。在PSCAD/EMTDC仿真环境下搭建了双端直流输电模型,验证了所提降容策略的有效性。最后从经济性角度对所提策略及现有环流抑制策略进行了对比分析,表明所提策略具有良好的经济性。

With the development of the flexible DC transmission techniques, the lightweight requirements of the converter valves have become increasingly urgent. The reduction of sub-module capacitance is difficult because of the requirements of the ripple amplitude of capacitor voltage, which is one of the key factors that affect the light weight of the valve. According to the characteristic that the fundamental frequency and second harmonic frequency components are the critical factors for voltage ripples, a novel strategy is proposed to reduce the voltage ripples of sub module capacitor by controlling the reactance value of the bridge arm. The bridge arm reactor switching circuit and switching control strategy are designed. The proposed strategy and the existing circulating current suppression control （CCSC） strategies are researched in terms of mathematical principles. A two terminal DC transmission model is built in PSCAD/EMTDC simulation environment, and the effectiveness of the proposed strategy is verified. Finally, the proposed strategy is compared with the CCSC strategy in the economic aspect and it is concluded that the proposed strategy has good economic performance.