混合多端直流输电系统柔直换流阀电气应力抑制策略研究

Control Strategy of Suppressing Sub-module Hybrid MMC Valve Electrical Stress on Multi-terminal Hybrid-HVDC System

混合多端直流输电系统中逆变站采用子模块混合型模块化多电平电压源换流器(MMC)并联,因此对子模块混合型MMC换流阀电气应力及抑制策略进行研究对于系统安全性和可靠性分析具有重要的意义。首先分析了混合多端直流输电系统运行原理;然后进一步分析了MMC换流阀电气应力产生机理,并在此基础上提出了MMC换流阀电气应力抑制策略;最后在PSCAD/EMTDC软件中建立3端LCC+MMC+MMC型混合直流输电系统,并对MMC换流阀电气应力抑制策略进行了仿真验证。通过本文研究可知,故障发生过程中非故障换流站持续注入能量是MMC换流阀电气应力增大的主要原因,采用泄能装置后可以有效抑制MMC换流阀的电气应力。

In hybrid multi-terminal high voltage direct current system, inverter is designed for paralleled two hybrid modular multilevel converter（MMC）. Valve electrical stress and its control strategy of the hybrid sub-module MMC is very critical for power transmission stability and engineering feasibility of hybrid multi-terminal HVDC transmission system. Firstly, the operation mechanism of hybrid multi-terminal system is analyzed. Based on this,the valve electrical stress control strategy is proposed in detailed. Finally,LCC＋MMC＋MMC（sub-module MMC） three terminal hybrid-HVDC transmission system model is built by PSCAD/EMTDC, and valve electrical stress and its control strategy are simulated. According to the analysis result, the main factor of valve electrical stress of sub-module MMC is the energy from non-fault converter station continuous injection into failure station during the fault occurrence. The valve electrical stress level of sub-module MMC of multi-terminal hybrid HVDC system could be suppressed effectively by energy release device.