模块化多电平换流器子模块关键组部件稳态电流应力全解析化计算

Steady-state Current Stress Fully Analytical Calculation of Components in Sub-modules of Modular Multilevel Converter

模块化多电平换流器(modular multilevel converter,MMC)是当前柔性直流工程的主流拓扑。高压大容量柔性直流输电工程中,MMC子模块中的半导体器件,特别是绝缘栅双极型晶体管(insulated gate bipolar transistor,IGBT)的通流能力较弱,电流安全裕度较小,对各半导体器件的稳态电流应力进行精确解析计算对换流器器件选型、换流器损耗计算、阀冷系统设计、换流阀运行状态评估等具有决定性的作用。同时,支撑电容器也是模块的关键组部件,电流是其研发的关键指标。该文基于MMC子模块各组部件的通流条件和平均开关函数模型,推导了各组部件的电流平均值和电流有效值等关键参数的精确解析表达式,并进一步分析了MMC处于整流状态和逆变状态时各器件稳态电流应力的大小关系及特征。通过将稳态电流应力的解析计算结果与电磁暂态仿真结果进行对比,验证了该文提出的解析计算方法的精确性。最后,基于解析计算和仿真分析,揭示了各组部件电流应力分布的特征规律。

Modular multilevel converter(MMC)is the main topology for the voltage source converter-based high voltage direct current(VSC-HVDC)project.The current through-flow capability of the semiconductor devices,especially that of the IGBTs of the MMC,is weak and the safety margin is small in high-voltage VSC-HVDC projects with large capacity.So it is decisive to calculate the steady-state current stress of the semiconductor devices accurately for the device selection,the converter loss calculation,the design of the valve cooling system,the valve operation state estimation and so on.Also,the supporting capacitor is the key component of the submodule,and its current is the key parameter to be considered when being developed.In this paper,the accurate analytical expression of the average value of the current,and the root-mean-square value of the current of the components in sub-modules are deduced,based on the current through-flow conditions and the average switching function model.Furthermore,the current stresses of the four devices are compared and their characteristics are analyzed when the MMC is in the converter and the inverter states.With the comparison of the analytical calculation results and the electromagnetic simulation results of the steady state current stress of the devices,the accuracy of the proposed analytical method is validated.Finally,the characteristics of the current stress distribution of the components are revealed based on the analytical calculation and simulation analysis.