C-MMC型电力电子变压器直流故障分析与保护方法研究

Study on DC fault analysis and protection method of C-MMC based power electronic transformer

对模块化多电平换流器(Modular Multilevel Converter,MMC)型电力电子变压器的拓扑结构及实现原理进行介绍。分析了在采用半桥子模块的MMC中发生中压直流母线双极短路故障后的电流流通路径,以及其不能实现直流故障闭锁的原因。为解决上述问题,选取箝位双子模块代替半桥模块,并分析了其故障电流流通路径和故障闭锁原理。但由于箝位双子模块在直流故障闭锁后可能出现子模块过电压问题,为此,提出了电力电子变压器隔离级延时闭锁的策略,并分析了MMC闭锁后在该策略下隔离级闭锁前的故障电流流通路径。最后,通过PSCAD仿真平台对箝位双子模块的闭锁功能和隔离级延时闭锁策略进行了仿真验证。

The topological structure and implementation principle of modular multilevel converter(MMC)based power electronic transformers were introduced in this paper.The current path of the MMC with half-bridge sub-module in the presence of medium-voltage DC bus double pole short-circuit fault,and the reasons of failing to achieve DC fault blocking were analyzed.In order to solve the above problems,the clamp double sub-module was selected to replace the half-bridge sub-module,and the fault current path and the fault blocking principle were analyzed.However,the overvoltage of the clamp double sub-module may occur after the DC fault blocking.Therefore,the delay blocking strategy of isolated stage for power electronic transformer was put forward,and the fault current path before isolation and after MMC blocked was analyzed.Finally,the blocking function of clamp double sub-module and isolation level delay blocking strategy were simulated and verified by PSCAD simulation platform.