MMC型换流器电容电压波动抑制方法研究

Study on the Suppression Strategy of Capacitor Voltage Fluctuation of MMC Converter

为了解决模块化多电平换流器(MMC)电容电压波动导致的换流器成本与体积增加等问题,提出了一种电容电压二倍频纹波抑制方法。首先从能量脉动角度推导了电容电压波动的数学模型,比较了不同二倍频环流对MMC电容电压波动抑制效果的影响;然后采用Clark变换将桥臂共模电压分解为αβ轴分量,利用准比例谐振控制器生成桥臂环流参考值,设计内环控制器对外环控制器生成的桥臂环流参考值进行跟踪,从而抑制子模块电容电压波动;最后在MATLAB/Simulink仿真系统上对所提控制策略进行仿真验证,通过对比传统环流抑制策略与所提控制策略对电容电压波动的抑制效果,证明了所提方法可有效抑制电容电压波动,改善输出电压的波形质量。

In order to solve the problem of cost and volume increase of modular multilevel converter(MMC)caused by capacitor voltage fluctuation, this paper presents a new method to suppress the double fundamental frequency ripple of capacitor voltage. Firstly, the mathematical model of capacitor voltage fluctuation is derived from the perspective of energy fluctuation, and the influence of different double fundamental frequency circulating current on MMC capacitor voltage fluctuation is analyzed. Then, the bridge arm common-mode voltage is decomposed into α-β axial components by using Clark transform, and the quasi-proportional resonance controller is used to generate the reference bridge arm circulating current. The inner loop controller is designed to track the reference bridge arm circulating current generated by the outer loop controller to suppress the capacitor voltage fluctuation of the submodule. Finally, the proposed control strategy is simulated and verified on the MATLAB/Simulink simulation system. By comparing the suppression effect of the traditional circulating current suppression strategy and the proposed control strategy on capacitor voltage fluctuation, it is verified that the proposed control method can effectively suppress capacitor voltage fluctuation and improve the waveform quality of output voltage.