HHybrid HVDC circuit breaker is mainly composed of fast mechanical switch and power electronic device

which mainly relies on fast mechanical switch to carry current and break and close current through power electronic device.It provides DC side short circuit protection for flexible HVDC transmission.However

the breaking current of DC circuit breaker is larger than that of IGBT’s normal capacity.According to the special working conditions and electrical stress of the IGBT of the DC circuit breaker

this paper analyzes the factors that affect the improvement of the IGBT’s turning off capacity and improves the turning off current capacity of the IGBT from three aspects:reducing the turning on loss

turning off loss and restraining the IGBT turning off overvoltage.In this paper

the influence of different circuit parameters on IGBT loss is firstly simulated.The IGBT’ s turning off loss is reduced by optimizing the desaturation ability and the turning off transient characteristics of IGBT

and finally the junction temperature simulation check of IGBT is completed.Meanwhile

by studying the influence factors of IGBT turning off overvoltage and simulating the influence of different circuit parameters on IGBT turning off overvoltage

the specific method of suppressing the turning off transient overvoltage of IGBT is proposed.Through the development of 50 kV transfer branch valve group and the establishment of test platform

this paper completes the large current breaking of 26 kA and the IGBT steady-state loss and transient loss are effectively controlled.The research results have been successfully applied to the ±535 kV hybrid high-voltage DC circuit breaker project of Zhangbei project

which is of great engineering signific ance.