Peak voltage stress on stator winding in PWM inverter fed drives

The high frequency model of electrical machines is instrumental in assessing undesirable effects in inverter fed electric drives, such as excessive voltage stress in machine windings, electromagnetic interferences, and bearing current due to common mode voltage, and onset of partial discharge that may severely reduce machine lifetime. Herein, a high frequency model of a random wound stator winding is developed, which depicts the behavior of the machine over a wide range of frequency, from 1 Hz to 10 MHz. The developed model is used to study the voltage distribution in the stator winding under PWM excitation. As is illustrated, besides high voltage stress at the machine terminals due to impedance mismatch between the machine and the cable, the peak voltage stress occurs across the turns close to the neutral point. This phenomenon, which has not been reported in the literature due to inadequate understanding in this subject field, is fully analyzed and experimentally validated. The model developed in MATLAB/Simulink environment is validated experimentally on an automotive-grade 60 kW permanent magnet synchronous machine adapted in Toyota Prius vehicle.