混合型MMC的开关频率优化控制算法

Optimal Switching Frequency Control Algorithm for Hybrid MMC

混合型模块化多电平换流器MMC(modular multilevel converter)的桥臂由半桥子模块HBSM(half-bridge sub-module)和全桥子模块FBSM(full-bridge sub-module)组成,损耗低、成本低,同时具有故障穿越能力。但是,子模块SM(sub-module)电容均压会造成较高开关频率,导致开关损耗较大。为了解决该问题,研究了基于混合型MMC的开关频率优化控制策略,将保持因子引入混合型MMC模型,通过数学推导,设计了基于电容电压波动率的保持因子控制器。仿真结果表明,开关频率优化控制算法在保持均压效果的前提下,有效降低了开关频率,在高压直流输电等领域具有理论意义和工程实践价值。

Each bridge arm of a hybrid modular multilevel converter(MMC)is composed of half-bridge sub-modules(HBSMs)and full-bridge sub-modules(FBSMs),which can maintain the fault ride-through capability while possessing the advantages of low loss and low cost.Among them,the capacitor voltage sharing of sub-modules(SMs)will cause a high switching frequency and a large switching loss.To solve this problem,an optimal switching frequency control strategy based onhybrid MMC is studied.Anretention factor is introduced into the hybrid MMC model,and a retention factor controller based on the capacitor voltage fluctuation rate is designed through mathematical derivation.Simulation results show that the optimal switching frequency control algorithm effectively reduces the switching frequency while maintaining the voltage sharing effect,which is theoretical significance of scientific research and engineering practice value in the fields including HVDC transmission.