MMC低开关频率的自适应降损控制策略

An adaptive loss reduction control strategy for MMC with low switching frequency

针对半桥型模块化多电平换流器(MMC),本文提出了一种低开关频率的自适应降损策略,解决了最近电平逼近调制(NLM)策略和基于排序算法的电容均压控制策略导致的换流阀功率器件开关损耗较高的问题。首先,分析了MMC内部悬浮电容均压效果与其开关频率间的制约关系,明确实际工程应用对子模块电容电压均衡性的要求,为后续低开关频率的自适应降损控制策略提供理论依据。其次,基于所设置子模块电容电压动态限值、流经子模块的电流方向以及子模块工作状态,确定每个周期内子模块投入优先级,从而减少非必要的子模块附加投切动作,降低子模块开关频率。然后,利用线性插值方法,实现不同系统传输功率下子模块电容电压动态限值的自适应调整,进一步降低子模块开关频率。最后,基于在Matlab搭建的MMC仿真模型,验证了本文所提方法。

For the MMC with HBSM,an adaptive loss reduction control strategy with low switching frequency is proposed to solve the problem of high switching loss of converter valve caused by the nearest level modulation(NLM)strategy and sort based capacitor voltage balancing control strategy.Firstly,the relationship between the capacitor voltage balancing effect and the switching frequency is analyzed,and the requirements for capacitor volt⁃age balancing in practical engineering applications are clarified,providing a theoretical basis for the subsequent a⁃daptive loss reduction control strategy with low switching frequency.Secondly,based on the dynamic limit values of the capacitor voltage,the direction of the arm current and the switching status of the submodules in the previous control cycle,the priority of submodule in the current control cycle is determined.The unnecessary extra switching actions of the submodules are reduced.Then,the linear interpolation method is used to realize the adaptive adjust⁃ment of the dynamic limit value of the capacitor voltage under different system transmission power,which further re⁃duces the switching frequency of the submodules.Finally,the MMC⁃HVDC electromagnetic transient simulation model with 200 submodules is built in MATLAB/Simulink to verify the proposed loss reduction control strategy.