Cable characteristic impendence and its influence on over-voltage at motor terminal

In PWM (Pulse Width Modulation) drive system, the reflected voltage in the cable transmission process can produce overvoltage and damped high-frequency ringing at motor terminals and further stresses the motor insulation, even leads to insulation breakdown in premature period. Those can undermine the stability of the PWM system. Firstly, in this paper, the cable equivalent mathematical model was founded based on three-phase cable. Then the propagation velocity, the oscillation frequency and the oscillation duration of the pulse in the cable is described by mathematical method, and the effects of cable parameters on over-voltage at motor terminals was analyzed under the conditions of high-frequency. Finally based on the simulation PSpice software, we tested and verified that conclusion by building simulation models.