Fault Simulation And Diagnosis Of Modular Multilevel Converter

Modular multilevel converter(MMC)is widely used in dc power transmission,new energy grid-connected power generation,transmission,reactive power compensation,flow control,etc.It has the characteristics of cascade inverter,modular structure.It is easy to change the number of level,and realize dc side back-to-back connection mode.It can be considered as a special form of cascade.Changing the number of sub-modules and connection way between them,and choose a reasonable control strategy,so we can get the required voltage grade.In high voltage applications,the number of sub-modules in every bridge increases,to ensure normal operation of system,module fault diagnosis and location becomes more important.The purpose of this paper is to explore the method of fault diagnosis and location of MMC sub-module(by a half bridge module structure).The main information derived from DC voltage,capacitance voltage of sub-module and three-phase current.Through analysising the power harmonic,the neutral point offset characteristics of the quantities above,the characteristics of sub-module IGBT device open circuit,short circuit,high impedance fault was summed up.This article introduces several modular multilevel converter topology analysis and comparison,and then introduced the working principle and mathematical model of double star modular multilevel converter.On the basis of analyzing the working principle and failure behavior of MMC,the five level MMC Simulink fault simulation platform based on MATLAB was built,sub-module IGBT device open circuit,short circuit and high impedance fault are simulated,and summarizes the characteristics of different fault in DC voltage,capacitance voltage of sub-module and three phase current,providing the basis for MMC fault diagnosis and location.