直流侧电压波动对MMC的环流影响机理分析及抑制方法

在基于模块化多电平换流器(MMC)的直流配电系统中,直流母线电压波动会在换流器内部激发环流.为了研究环流产生的机理,结合开关函数,对子模块电压波动和内部环流进行数学推导,得出环流幅值和频率的传导规律,并给出环流的解析表达式.为消除此环流的影响,基于快速全局最小二乘子空间旋转不变(TLS-ESPRIT)和比例积分?矢量比例积分(PI-VPI)设计了一种自适应环流抑制控制器.通过改变MMC调制函数来调节桥臂电压,使其跟随直流母线电压波动,从而实现环流抑制.在MATLAB/Simulink平台上进行仿真,结果验证了直流电压波动对MMC的影响机理的正确性,且所提控制策略将环流幅值抑制到原幅值的3.2％～～4.5％.

Analysis on Influence Mechanism of DC-side Voltage Fluctuation on Circulating Current of Modular Multilevel Converter and Its Suppression Method

In the DC distribution system based on modular multilevel converters (MMCs), the voltage fluctuations of the DC bus will generate the circulating currents in the converters. To study the generation mechanism of the circulating current, the voltage fluctuation and internal circulating current of the sub-module are deduced mathematically combined with the switching function. The conduction law of circulating current amplitude and frequency is obtained, and the mathematical expression of circulating current is proposed. To eliminate the influence of the circulating current, an adaptive circulating current suppression controller based on fast total least squares-estimating signal parameter via rotational invariance techniques (TLS-ESPRIT) and proportional integral vector proportional integral (PI-VPI) is proposed. By changing the modulation function of MMC, the bridge arm voltage is adjusted to follow the voltage fluctuation of the DC bus, which is able to suppress the circulating current. The simulation is carried out on MATLAB/Simulink platform. The results verify the correctness of the influence mechanism of DC voltage fluctuations on the MMC. Furthermore, the proposed control strategy can suppress the amplitude of the circulating current to 3.2%~4.5% of its original value.