Optimum design of snubber capacitors in 9 kW three-phase inverter for doubly salient permanent magnet motor

Single-chop upper switch hysteretic-current control strategy is used in three-phase full-bridge MOSFET inverter for a 9 kW 12/8-pole doubly salient permanent magnet (DSPM) motor. Due to high chopping frequency, MOSFET´s parasitics, the existence of parasitic inductance, and also instantaneous variation of winding back EMF and winding inductance, the working of the inverter is quite complicated, and significant voltage spike and current spike will appear each time when chopped upper MOSFETs turn off, which induces severe voltage and current stress on MOSFETs and reduces system reliability. Thus, effective and easy-to-implement snubbers are needed to release or resolve the above mentioned problem. The paper details the working of three phase snubbers, and gives design guidelines, heat dissipation analysis and cooling ways for snubber capacitors.