基于环流解析分析的MMC电容电压优化控制策略

Optimization Control Strategy of Capacitor Voltage for Modular Multilevel Converter Based on Mathematical Analysis of Circulating Current

为限制MMC子模块电容电压波动,一般所需电容较大。首先分析二倍频环流与电容电压波动间的解析关系,提出了全工况范围内的子模块电容电压波动峰值与二倍频环流之间关系的数学模型。然后利用该模型,提出以电容电压波动为目标值的二倍频环流注入方式,将电容电压波动峰值控制在设定参考值。该方法不仅能在在全工况下实现控制目标,而且通过减小峰值电流增加安全裕度。最后,通过仿真及试验结果验证了所提模型的正确性与优化控制策略的有效性。

Bulk capacitor is used to limit capacitor voltage ripple in modular multilevel converter(MMC). First,we propose a mathematical model which depicts the relationship between the peak value of capacitor voltage ripple and the 2 nd–order circulating current in various conditions by studying the analytic relationship between them. Then, the peak value of capacitor voltage ripple is controlled to the reference by injecting 2 nd –order circulating current with the aim of acceptable capacitor voltage ripple. The method can not only achieve the control destination, but also reduce arm current to improve margin of safety. Finally, the simulation and experimental results verity the validity of the proposed method.