Abstract: In the motor controller of new energy vehicles，due to insufficient current capacity，high cost，and

limited heat dissipation capacity，parallel power devices are often used to extend current 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. Firstly，the causes of current imbalance were summarized，and the current sharing coefficient，that is the unbalance ratio，was put forward as the measuring standard of current balance. The conduction resistance model based on thermal resistance was presented，and the influencing factors of steady current balance of parallel devices were analyzed. Then，based on the voltage and current curves in the variable resistance region，the influencing factors of dynamic current balance of parallel devices were analyzed. The effect of parasitic inductance on dynamic current balance was analyzed by PSPICE simulation，and the influence of parameter difference on current balance was analyzed. Different optimization methods were proposed for different parameter differences. Finally，the influence of EMI on the current sharing characteristics was analyzed，and the design of the drive circuit was suggested，and the optimization effect of the gate voltage waveform was verified in the simulation.

      Key words: power devices；parallel；current sharing；parasitics parameter