Reflected wave modeling techniques for PWM AC motor drives

Abstract

Reflected wave transient voltages that are impressed on drive output cables and low voltage AC induction motors are simulated with an excitation source of steep fronted d/spl nu//dt pulse waveforms from a pulse width modulated (PWM) voltage source inverter. Motivation for system simulation arises from a need to correlate reflected wave peak voltage and risetime with the dielectric insulation capability of both motor and cable. Simulations based on an accurate system model also allow investigation into the effects of changing wire gauge, motor HP, cable distance or addition of drive output filters. System parameters of the inverter, cable and motor model are investigated in detail. Special emphasis is given to the importance of modeling cable skin and proximity effects. Simulation, measured lab and field results are compared. The main objective of the paper is to propose a reflected wave building block model that uses existing software on the market, is simple, computationally fast, easily configurable, reasonably accurate and allows investigation with wide variation of system parameters.