Overvoltage mitigation of inverter-driven motors with long cables of different lengths

This paper presents an intensive discussion on an overvoltage appearing at the motor terminals of an adjustable-speed drive that consists of a voltage-source PWM inverter, an induction motor, and a three-phase symmetric long cable. It describes a design procedure for a simple passive EMI filter based on parallel connection of an inductor and a resistor, which is intended for mitigating the overvoltage at the motor terminals. The modeling of the cable and the motor are prominent in focusing on the natural frequency or ringing frequency inherent in the cable used, which is inversely proportional to cable length. Impedance mismatch at the inverter and motor terminals causes the overvoltage that may reach double the inverter dc-link voltage. The effectiveness and validity of the simple design procedure of the filter are confirmed on the 400-V, 15-kW experimental system with either a 100-m or 200-m-long cable, as well as on computer simulation based on the modeling of the cable and the motor.