Determination of Cable Characteristics and Adjustment of PWM Pulse Pattern to Minimize AC Motor Terminal Over-voltage

In this paper, a method to detect characteristic impedance and oscillation frequency of a cable in an AC drive system is developed. Results are provided for different cable constructions and lengths. The application of the measured oscillation frequency to adjust the PWM pulse pattern for reflected wave motor over-voltage reduction, with reduced distortion in the output voltages, is demonstrated. Experimental results are provided to show the applicability of the reflected wave compensation at higher switching frequencies. In addition to estimating the cable characteristic impedance, the cable peak charging currents can also be estimated, which can be used to accurately determine power module losses and predict the junction temperature.