交直流侧电流分别可控的模块化多电平换流器控制方法

摘要

对于模块化多电平换流器应用于柔性直流输电系统,由于已有的控制方法基于每相投入的子模块个数N不变的前提,因此,直流侧电压、电流不能直接控制,冗余模块得不到充分利用.文中提出的交直流电流分别可控的控制方法,其特点是N可变.首先在阀组级控制中合理安排投切子模块的个数、时机和选择方法,使N可以在一定范围内调节,然后在系统级控制中以有功、无功电流解耦控制和直流电流控制为内环,实现了换流器功率、电压控制策略.通过对71电平模块化多电平换流器仿真证明:该方法可以实现交流侧和直流侧电流的分别可控,具有良好的直流电容均压效果,当直流系统电压波动时可以抑制电容电压波动,维持稳定输出.%DC voltage and current of modular multilevel converter (MMC) in voltage source converter based high voltage DC (VSC-HVDC) system cannot be directly control in existing control strategy so as to without full use of the redundant sub-modules. The number of switched on sub-modules per phase N is a constant in existing control strategy. A controllable N strategy is proposed here. At first, on device level a switching algorithm, including number of switch on/off sub-modules, switching time and selection method is proposed so that make N controllable. Then based on the algorithm, AC and DC current hybrid control strategy is implemented on system level with the inner-loop of power/voltage control of the converter. The results of simulation with 71 level MMC illustrate that AC and DC current hybrid control strategy is successful and has good voltage sharing among capacitors in DC link of MMC. It also shows that when DC system voltage fluctuates, the DC voltages fluctuation of sub-modules can be suppressed so as to keep power output smooth.