模块化多电平变流器低频调速系统控制方法

A Low-frequency Control Scheme for Modular Multilevel Converter Motor Drive

详细分析了模块化多电平变流器能量流动情况,研究了变流器桥臂能量波动的原因,并指出桥臂能量波动与运行频率成反比,且当模块化多电平变流器调速系统在低频运行时,由于模块电容电压波动过大而无法正常工作。针对该问题,文中提出在桥臂共模电流中加入高频正弦分量,并同时在变流器输出共模电压中加入高频方波分量,从而在变流器上、下桥臂间引入高频能量交换,抑制模块电容电压波动。阻感及电机负载的实验结果证明,采用所提出的控制方法后模块电容电压得到有效的抑制,低频调速系统性能良好。

The process of energy flow of modular multilevel converter (MMC) is analyzed in detail,the cause of energy fluctuation is discussed and it is pointed out that the peak value of energy fluctuation is inversely proportional to operating frequency.When MMC motor drive is operated at low frequency,the fluctuation of modular capacitor voltage is so large that the motor drive cannot work normally.To solve this problem,this paper presents a control scheme,by which a high frequency sinusoidal component is incorporated in the arms”common-mode current and a high frequency square component in the output common-mode voltage simultaneously.Thus energy exchange between the upper arm and lower arm is realized to restrain voltage fluctuation.The experiment results show that the fluctuation of modular capacitor voltage is effectively restrained and the performance of the low frequency drive system is satisfactory.