基于选择性定频积分逼近调制策略的MMC子模块不对称运行控制方法

Selective Constant Frequency Integration Approaching Modulation Based Control Method for Sub-Module Asymmetric Operation of Modular Multilevel Converter

针对模块化多电平变换器子模块不对称运行问题,提出了一种基于选择性定频积分逼近的PWM调制策略。变换器由于元件损坏或参数差异会出现子模块电容电压失衡的不对称运行状态,周期性地监测子模块电容电压和桥臂电流方向,改变PWM驱动信号与实际开关管驱动的映射关系,使系统由不平衡运行状态回到平衡运行状态。此外,该调制策略有效减少了开关管驱动的窄脉冲、降低了开关损耗。仿真和实验验证了所提方法的有效性。

Due to element failure or differences among parameters, the asymmetric operation condition of the converter in modular multilevel converter （MMC） may be caused by the imbalance among capacitor voltages of sub-modules. To solve this problem, a selective constant frequency integration approaching modulation based pulse width modulated （PWM） strategy is proposed. In the proposed modulation strategy, the capacitor voltage of sub-modules and the current direction in the bridge-arms are periodically monitored to change the loop mapping relation between the driving signal of PWM and the driving of actual switching valves to make the MMC returning to balanced operation condition from unbalanced operation condition. Besides, the proposed modulation strategy can effectively reduce the number of the narrow pulse to drive the switching valves and switching loss can be correspondingly decreased. The validity of the proposed modulation strategy is verified by both results of simulation and experiments.