Simulation Research On Parallel Technology Of Discrete Power Device Of Electric Vehicle Inverters

Due to insufficient current capacity,high cost,and limited heat dissipation capacity,parallel power devices are often used to extend power capability of power inverter for EV applications.Current imbalance can be caused by device parameter tolerances,parasitic parameter inconsistencies due to asymmetric PCB layout,and heat accumulation due to the cooling effect of the heat sink.Current imbalance of power device will lead to the different in junction temperature of device.At the same time,the high frequency signal in current will shorten the life of the bearing.In order to balance the current of parallel MOSFET,the current sharing of MOSFET is analyzed and optimized in this paper.In this paper,the physical characteristics and switching characteristics of MOSFET are analyzed.Based on the physical characteristics of MOSFET,the equivalent model of MOSFET is established.The equivalent mathematical models of the conducting stage and the switching stage are respectively given.In order to study the influencing factors of parallel current sharing,a parallel current sharing circuit model of MOSFET with parasitic parameters was established,and the relationship between static current sharing and dynamic current sharing and device parameters and thermal resistance was analyzed.Aiming at the problem of parasitic parameters in circuit design,the influence of parasitic parameters on parallel current sharing is analyzed in detail.A double pulse test circuit model based on PSPICE is established to verify the correctness of the theoretical analysis.In order to solve the problem of current imbalance,this paper firstly introduces some current sharing optimization methods,the deficiency of gate asynchronous drive is analyzed,and a parallel current sharing circuit based on coupling inductance and dynamic gate drive is proposed and its working principle is analyzed.A parallel current sharing circuit based on PSPICE is established to verify the improvement effect of the proposed method on parallel imbalance current,and it can optimize both dynamic and static current unbalance.Finally,the thermal unbalance and bearing current problems caused by imbalance current sharing in practical operation are analyzed.Under the condition of tight thermal coupling,the parallel uneven flow will not lead to serious thermal unbalance,so no measures need to be taken.Through simulation,the optimization effect of current sharing measures combined with coupling inductance and dynamic gate drive on bearing current is verified.This method can effectively suppress the high frequency noise caused by current unbalance,so as to reduce the bearing current.