Research On Fault Diagnosis And Tolerance Technology Of Switch On Module Multilevel Converter Based On Capacitance Voltage Balance Control

With the development of HVDC,Modular Multilevel Converter(MMC)is more and more widely used because of its huge advantages.However,the use of many switches causes the probability of its failure to increase.Therefore,it is of great significance to study the open circuit fault diagnosis and fault-tolerant control technology of MMC switch tube in order to improve the reliability of converter and to promote its application in DC transmission and motor drive.The MMC studied in this paper adopts single phase independent load topologies and carrier phase shift modulation strategy.The working principle of MMC is analyzed and the mathematical model of the system is established.This paper introduces two capacitor voltage balancing algorithms based on carrier phase shift modulation strategy,and analyzes the advantages and disadvantages of the two balance algorithms.This paper studies the reason why the capacitor voltage balancing algorithm based on ranking method may lead to the failure of the commonly used fault location method according to the comparison between the actual value of the capacitor voltage and the reference value and proposes a method by comparing the ideal value of the capacitor voltage and the actual value,the metod can not only detect the fault but also locate the fault sub module.The final simulation verifies the feasibility of the method.The scheme of cold redundancy and hot redundancy is studied.The reason of the current impact caused by the fault tolerance scheme is analyzed.A fault-tolerant scheme of non-redundant submodule is designed,which includes symmetric and asymmetric ablation.It does not need additional redundant modules,saves costs and is simple to implement.Finally,the advantages and disadvantages of each scheme of cold standby redundancy and hot standby redundancy and fault tolerance of non-redundant sub-module are compared by simulation analysis.Finally,this paper designs and builds a 8 module MMC prototype.The experimental results show that the proposed fault diagnosis and design of redundancy-free sub-module fault-tolerant scheme is effective.