基于能量平衡的降低模块化多电平变换器子模块电容电压波动控制策略

电容器是模块化多电平变换器(MMC)子模块的关键部件,降低子模块电容电压波动是提高电容器可靠性和降低变换器成本的双重要求。首先分析不同环流对MMC电容电压波动的影响,指出注入典型2次环流是降低电容电压波动和减少器件损耗较好的折中方案。然后,在介绍已有基于工频周期的能量平衡控制策略基础上,提出基于控制周期的能量平衡控制策略,在达到注入典型2次环流降低MMC电容电压稳态波动的同时又能取得较好的暂态性能。所提出的基于能量平衡的控制策略,与常规PI控制器相比避免了繁琐的参数整定过程,并适应各种工况。最后,通过仿真和实验验证了所提控制策略的有效性。

Control Strategy Based on the Energy Balance for Reducing Sub-Module Capacitor Voltage Fluctuation of Modular Multilevel Converter

Capacitors are the key elements in the sub-modules of the modular multilevel converter (MMC). Reducing sub-module capacitor voltage fluctuation is a dual requirement to improve capacitor reliability and reduce converter costs. Firstly, the influence of different circulating currents to the capacitor voltage fluctuation is analyzed in this paper. It is shown that injecting the typical 2nd order circulating current can reduce the capacitor voltage fluctuation greatly without increasing too much loss. Secondly, after introducing the existing energy-balance based control strategy with the line-cycle time scale, the control strategy with the control-cycle time scale is proposed. It can reduce the capacitor voltage fluctuation by injecting the 2nd order circulating current and improve the transient performance at the same time. Compared with the traditional proportional-integral controller, the proposed energy-balance based control strategy avoids the complicated adjusting process of parameters, which can be used in various conditions. Finally, both simulation and experimental results verify the proposed control strategy.