Transient modeling and analysis of motor terminal voltage on PWM inverter-fed AC motor drives

This paper presents new concepts in the modeling and analysis of transient overvoltage and ringing associated with PWM inverter-fed AC machines. Experimental results are presented which demonstrate that frequency response (based on a typical AC induction machine´s impedance) behaves like a capacitance-resistance network rather an inductance-resistance network in the high frequency range. Traveling wave reflection phenomena (as a result of the drive system) are analyzed considering motor capacitance. The following two transient stages are proposed to describe the motor voltage waveforms observed: (1) traveling wave reflection and (2) inductance-capacitance ringing. Criteria determining the maximum overvoltage at the motor terminals are discussed including design considerations for an artificial RC terminator. The analytical estimations and simulations for transient voltage based on the hypothesis are confirmed with both laboratory and field results.