Filtering techniques to minimize the effect of long motor leads on PWM inverter-fed AC motor drive systems

In this paper, filtering techniques are investigated to reduce the motor terminal overvoltage, ringing, and dv/dt in inverter-fed AC motor drive systems where long leads are required. Analysis is presented to show that the distributed LC of a cable and the pulse-width modulated (PWM) inverter switching action lead to motor terminal voltage reflections and ringing that stress the turn insulation and contribute to bearing currents. First- and second-order shunt filter designs are analyzed and compared. Detailed design equations to match the filter impedance to the cable surge impedance and to determine the filter component values are presented. It is demonstrated that a first-order shunt filter connected at the motor terminals significantly reduces the overvoltage stress and ringing, and also lowers the dv/dt of the PWM switching pulse. Simulation and experimental results are presented to verify the proposed filter designs for 50-ft and 100-ft cable lengths for 460-V PWM insulated gate bipolar transistor (IGBT) AC motor drive systems.