Development Of 6kV DC Solid State Circuit Breaker Based On Cascade Of SiC JFETs

With the goal of "carbon peaking" and "carbon neutrality" being put forward,and distributed energy and DC loads increasing day by day,the DC power system has attracted great attention from scholars because it is more compatible with the access of distributed energy and DC loads.Due to the existence of large-capacity capacitors on the bus side of the DC system and the low impedance characteristics of the DC line,a large transient current will be generated when a short-circuit fault occurs in the DC system,and the fault isolation speed is demanding.Therefore,a safe and reliable DC protection device is one of the key technologies to promote the further development of the DC system.The solid-state DC circuit breakers based on the power semiconductor device as the main switch can better meet the harsh requirements of the DC system for fault isolation due to its unique fast arc-free fault current cutoff characteristics.The third-generation semiconductor devices represented by SiC will promote the further development of solid-state DC circuit breakers due to their low on-resistance,high withstand voltage,and high temperature tolerance.However,limited by the withstand voltage rating of semiconductor power devices,solid-state DC circuit breakers are currently mainly used in lowvoltage fields.Researching the series technology of power semiconductor devices is an effective way to improve the voltage level of solid-state DC circuit breakers.The main research contents of this paper are as follows:Firstly,in order to improve the voltage level of DC solid-state circuit breakers,the series technology of SiC JFETs is researched.The turn-off process of SiC JFET and the factors affecting the voltage withstand of cascading SiC JFETs are analyzed,and a novel cascading method of multi-SiC JFETs based on module cascading is proposed,which can effectively suppress the overvoltage of each SiC JFET,ensure that the dynamic and static voltage of the SiC JFET is within a safe range during the turn-off process,and realize the safe and reliable cascade of multiple SiC JFETs.This method consists of two parts: one is a single-gate driver cascaded SiC JFETs topology which is used to form the module,the other one is an active clamp control strategy which ensures that each module is protected from overvoltage when modules are cascaded.The topology,working principle and selection of key device parameters of the method are analyzed in detail.The effectiveness of the new SiC JFETs cascading method proposed in this paper is verified by simulation and experiment,which provides a new idea for the design of medium-voltage DC solid-state circuit breakers.Secondly,in order to realize the fast protection of the DC system under different fault types,a programmable,ultra-fast 6kV DC solid-state circuit breaker based on the cascade of 10 SiC JFETs was developed.The designed circuit breaker is composed of a detection module,a control module and a solid-state switch module.The detection module samples the current on the bus,and the control module judges whether there is a fault and the type of fault according to the bus current signal,and sends control signals.The solid-state switch module receives the control signal.When a fault occurs,the solid-state switch module quickly drives the SiC JFETs to turn off,completing the process of fast arc-free removal of the fault current.The overall topology and basic working principle of the circuit breaker are introduced,the circuit structure and working principle of each part are analyzed in detail,and the operation program of the circuit breaker is designed.The functional characteristics of the circuit breaker are verified by the experimental prototype,which ensures the rapid fault isolation of the DC system when different faults occur.