Research On DC Solid State Circuit Breaker Based On SiC MOSFET

With the development of DC microgrid,DC circuit breaker,as a key protection device to achieve fast and accurate fault isolation,provides a strong guarantee for the safety of DC microgrid.Due to the long action time of mechanical DC circuit breakers and the complicated circuit and control strategies of hybrid DC circuit breakers,DC solid-state circuit breakers are widely used in DC microgrids because of their fast action speed and simple circuit structure.Compared with Sidevices,SiC devices have lower on-resistance,faster switching speed,and stronger high-voltage and high-temperature resistance.Using them as switching elements of DC solid-state circuit breaker can greatly improve the breaking capacity,action speed and power density of DC solid-state circuit breaker.In this thesis,combined with the performance advantages of SiC MOSFET,a DC solid-state circuit breaker scheme based on SiC MOSFET is studied to improve the accuracy,quickness,safety,automation and controllability of DC solidstate circuit breakers.First,the working characteristics of SiC MOSFET are studied.On the basis of introducing the structure and working principle of SiC MOSFET,the dynamic and static characteristics of SiC MOSFET and SiMOSFET are compared and studied,the influence of device parameters on the characteristics is analyzed,and the advantages of SiC MOSFET in terms of on-resistance and switching speed are verified.Combined with the short-circuit scenario of DC solid-state circuit breakers,the influence of different circuit parameters on the short-circuit characteristics of SiC MOSFET is studied,which provides a basis for the selection of driving circuit parameters of SiC MOSFET and the topology design of DC solid-state circuit breaker.Secondly,the DC solid state circuit breaker scheme based on SiC MOSFET is studied.In order to directly limit the maximum short-circuit current and reduce the influence of the currentlimiting inductance on the transient response of the circuit and the turn-off overvoltage of the device,the "double conduction branch" topology in this thesis is designed.Aiming at the problem of false shutdown caused by startup inrush current,a control strategy combining dualthreshold protection control and peak current control are designed,and two protection modes are set for the DC solid-state circuit breaker according to the dual-threshold protection control:overcurrent protection mode and current-limiting protection mode In the current-limiting protection mode,the short-circuit current can be limited by the peak current control.Combined with the topology and control scheme of DC solid-state circuit breaker studied in this thesis,five working modes of DC solid-state circuit breaker are analyzed,and eight switching relationships between five working modes under different fault conditions are summarized.Finally,based on the control scheme and application scenarios of the DC solid-state circuit breaker in this thesis,the main parameters are designed and selected,a simulation model is built,and eight faults conditions are simulated.The simulation results show that the DC solid-state circuit breaker can accurately distinguish different types of faults and realize the corresponding working mode switching.When the starting inrush current is large,it can realize the currentlimiting of the starting inrush current and avoid "false shutdown".After the DC solid-state circuit breaker is closed,it can automatically reset and restart when the fault disappears.The low-power experimental prototype of the research scheme is made and eight short-circuit fault tests are carried out in turn.The experimental results are consistent with the simulation results,which further verifies the feasibility of the DC solid-state circuit breaker scheme in this thesis.