Design considerations for an inverter output filter to mitigate the effects of long motor leads in ASD applications

In this paper, design considerations for an inverter output filter to mitigate the effects of long motor leads in ASD applications are presented. It is shown by analysis that for a given length of cable, reducing the dv/dt of the PWM inverter output voltage applied to the cable below a critical value will eliminate overvoltages due to voltage reflections. Design issues for a low pass filter at the inverter output terminals to reduce the dv/dt of the inverter output pulse are examined in detail. The filter operation is verified for the entire variable frequency range of the inverter. The performance of the filter is evaluated in simulation, and experimentally on a 208 V L-L system and on a 480 V commercially available AC motor drive (PWM IGBT). The proposed inverter output filter is then compared with a motor terminal shunt filter also designed to reduce overvoltages and ringing at the motor terminals.