MMC静态直流充电时电容均压特性研究和保护定值整定

Voltage-sharing Characteristics and Protection Value Setting of Modular Multilevel Converter at Static DC Charging State

模块化多电平换流器在静态直流充电时存在电容电压两极分化的问题,部分子模块甚至因电压跌落导致反复启动。先通过引入取能电源等效阻抗动态参数改进子模块等效模型,然后根据改进后模型仿真分析了电容电压两极分化的机理,最后在仿真基础上提出了静态直流充电耐受时间定值整定方法,通过优化保护定值降低电容电压两极分化程度。依托厦门柔性直流输电工程进行了静态直流充电和单个阀塔加压试验,试验结果与仿真结果基本一致,验证了所提子模块等效模型、电容电压两极分化机理分析和保护定值整定方法的正确性。

A common problem in the static DC charging process of modular multilevel converter is voltage polarization. Some submodules＇ voltage sags even cause startup and shutdown repeatedly. In order to analyze the voltage-sharing characteristics of MMC,firstly, equivalent impedance of energy-absorbing source is introduced into the simulation model of sub-module; secondly, the mechanism of voltage polarization is studied based on the improved model; finally, a setting process of static DC charging tolerance time protection is proposed which can reduce the degree of voltage polarization. The static DC charging experiment and single tower test are conducted at Xiamen HVDC flexible transmission project and the results show consistence between simulation and experiment,which prove the feasibility of the improved simulation model of the sub-module, the mechanism analysis result of voltage polarization,the correction of static DC charging tolerance time protection value setting method.