Investigation Of Temperature Characteristics And Fast And Reliable Interruption Technology Of SiC MOSFET For Low Voltage DC Solid State Circuit Breaker Application

DC microgrids which is more efficient for distributed new energy is significant to energy sustainable development and energy-saving and emission-reduction.However,the absence of protection technology restricts the application of DC microgrid.Since solid-state DC circuit breaker has advantages of simple structure,fast interruption of fault current,arc free operation,reliable performance and limit the level of fault current,it is the development direction in the protection of DC DC microgrid.Currently,because of high conduction loss,low work junction temperature,low withstand voltage,performance affected significantly by temperature,the promotion and application of Si power device-based solid-state circuit breaker is limited.Compared to Si power device like Si MOSFET or Si IGBT,SiC power device such as SiC MOSFET exhibits higher voltage-blocking capability,higher temperature operature capability,faster switching speed,much lower on resistance.And also,its performance is less dependent on the temperature.As a result,the SiC MOSFET provides possibility for fast and reliable turn-off capability of solid-state circuit breaker in DC microgrid.However,fault current increases rapidly after fault in DC microgrid and the device junction temperature also increases significantly,which make device operature in high temperature state.Dynamic and static characteristics of device will be affected,as well as well as feature parameters.Due to fast switching speed and high variation in current,circuit breaker are prone to the transient overvoltage and oscillation phenomena.In addition,in order to make sure the operation of circuit breaker,a reliable fault current detection method is also indispensable.In order to give full play to the superior performance of SiC power devices and ensure that the DC solid state circuit breaker based on SiC MOSFET makes a response to the fault quickly and reliably,in this paper,the effects of temperature on performance of SiC MOSFET are analyzed.And,an voltage overshoot suppression and fault current detection for SiC MOSFET-based DC Solid-state circuit breaker are proposed.The investigation work in this paper mainly includes:（1）Aimed the absence of effective methods for SiC MOSFET gate capacitances parameters extraction,such as C_GS and C_OX,which affects simulator models,a method based on constant current source circuit is presented.Firstly,based on the typical resistive load circuit,the operation principle of presented method is analyzed in detail.Secondly,the extraction experiment is carred out for a certain SiC MOSFET.The comparison between experiment data and datasheet results show good agreement with each other,which proves the validity of presented method.Finally,the effects of load,system voltage and temperature on the presented method is investigated.（2）Aimed at the changes of performances of device caused by temperature in the interruption process of fault current,the effects of temperature on performances of SiC MOSFET are investigated.Firstly,the static characteristics of SiC MOSFET under different temperatures are measured,like transfer characteristic,output characteristic,threshold voltage and on-state resistance.Secondly,the effects of temperature on dynamic characteristic of SiC MOSFET under different load current,supply voltage and gate resistance are investigated,especially the variation in voltage and current.In addition,the short circuit characteristics under different tempareture are also measured.Finally,an equivalent circuit model of SiC MOSFET is established based on the experimental results.And the effectiveness of the established model is verified.（3）Aimed at the the transient overvoltage and oscillation phenomena in a solid-state DC circuit breaker based on SiC-MOSFET caused by its high switching-off speed,a suppression method that a metal oxygen varistor（MOV）is used as the snubber circuit is proposed.Firstly,according to the eatablished model of SiC MOSFET,an model of SiC MOSFET-based DC solid state circuit breaker is established,and the impact of different stray inductances in energy absorption branch of breaker is analyzed on the turn-off initial stage voltage waveforms.Secondly,the operation principle of the proposed method is analyzed,and the simulation researches on the suppressive effects are also conducted.Furthermore,a basic principle is presented on how to select the snubber MOV.Finally,the effectiveness of proposed suppression method is verified by experimental test.（4）Aimed at the fault current detection for SiC MOSFET-based DC Solid-state circuit breaker,a detection method based on the variation of gate voltage of SiC MOSFET is proposed.Firstly,according to the short circuit characteristic of SiC MOSFET,the operational principle of proposed method is analyzed.The related logic processing and control circuit are also designed,as well as the timing chart under normal operation and fault conditions.Secondly,the short circuit characteristic of SiC MOSFET and the effects of different environmental factors are investigated by simulation.The effectiveness of proposed fault current method is demonstrated by simulation and experimental test.Finally,based on above obtained results,a solid state DC circuit breaker prototype is designed and implemented.And also,the performance of the prototype is tested and analyzed.The obtained research achievements can provide theoretical references for optimal design and safe and reliable operation of DC solid state circuit breaker in low voltage application.Furthermore,it will be a great helpful to design high voltage DC circuit breaker.