应用于风力发电的MMC子模块新型电容降容控制

模块化多电平换流器(MMC)因其多方面优势适用于中压及更高电压等级的风力发电,但由于风电机组的低频大电流工况,机侧MMC子模块电容电压波动大,需要大的直流滤波电容。提出一种在负序二倍频环流控制器中注入环流来抑制子模块电容电压波动的策略,指出了所注入的环流的初相角的选择依据,并给出了基于该方法的子模块电容容值选取依据。针对该策略带来的环流二倍频分量增加的问题,提出了一组表征子模块电容电压抑制效果相对于环流增加量的折中系数,指出需根据系统要求来选择不同的折中系数作为评价标准,以达到所需求的总体性能。基于MATLAB/Simulink的仿真结果验证了理论分析的正确性和所提控制策略的有效性。

Capacitance Reduction Control for Sub-module of Modular Multilevel Converter Applied in Wind Power Generation

Modular multilevel converter(MMC)is very suitable for medium voltage and high voltage wind power generation system due to its advantages in many aspects. However, the capacitor voltage of each sub-module(SM)fluctuates widely in low frequency large current condition of the generator, which leads to large capacitors of the SMs. A novel method is proposed to suppress the capacitor voltage fluctuation of the SM with the circulating current injection based on the negative sequence double frequency circulation controller. And the basis is given for choosing the initial phase of the injected circulating current and the choice of SM capacitance based on the method. For the increase of the double frequency circulation with this strategy, a set of tradeoff coefficients characterizing the effect of voltage suppression relative to the increase of circulating current is presented. It is pointed out that the coefficient should be chosen according to the system requirements to meet the overall performance. Simulation results based on MATLAB/Simulink verifies the effectiveness of the proposed control strategy.