一种新型的混合MMC预充电策略

A New Precharging Strategy for Hybrid MMC

模块化多电平换流器(MMC)的预充电是保证MMC-HVDC系统正常运行的基础,其中同时包含全桥子模块(FBSM)和半桥子模块(HBSM)的混合型MMC拥有较强的直流故障穿越能力而成为研究的热点。由于全桥子模块和半桥子模块的充电特性不同,子模块(SMs)的电容器电压在不受控制的预充电过程结束时可能会有所不同。通过分析指出了混合型MMC常规不控充电策略的缺陷,然后提出了一种三阶段预充电策略。该策略可以消除不同类型子模块的电容电压不平衡,解决了半桥子模块预充电过程中自取能量不成功的问题。最后,基于所提出的策略对不受控预充电过程进行了仿真和分析。

Precharging process of the modular multilevel converter(MMC)is the basis to ensure the normal operation of MMC-HVDC system.The hybrid MMC,which includes both full-bridge sub-modules(FBSM)and half-bridge sub-modules(HBSM),has DC fault ride-through capability and has become a hot research topic.Due to the different charging characteristics of the full-bridge sub-module and the half-bridge sub-module,the sub-modules(SMs)capacitor voltages may be different at the end of the uncontrolled precharging process.Based on analysis,the defects of the conventional uncontrolled charging process of hybrid MMC were pointed out.Then a three-stage precharging strategy was proposed.This strategy can eliminate the capacitor voltages imbalance of different types of SMs and solve the problem of unsuccessful self-taking energy during HBSM precharging process.Finally,simulation and analysis of the uncontrolled precharging process based on the proposed strategy were carried out.