Design and Implementation of a dv/dt Filter for Motor Overvoltage Mitigation in SiC-Based Adjustable Speed Drives

In SiC-based adjustable speed drives, the fast-switching voltage pulses are reflected at motor terminals due to the impedance mismatch between the cable and motor, resulting in severe overvoltage at motor terminals. One effective solution to tackle this issue is installing passive filters at the inverter side to reduce the dv/dt of the voltage supplied to the motor drive system. However, the conventional dv/dt filter design approaches solely focus on the filter's design for a specific dv/dt without fully considering the influence of the cable and motor. This oversight can lead to suboptimal designs in terms of the filter's output performance and its effectiveness in mitigating the motor overvoltage. To address these gaps, this paper proposes a dv/dt filter design approach for motor overvoltage mitigation, investigating the influence the cable and motor impedance on the filer's performance. Three RLC dv/dt filters that have similar output voltage waveforms are designed and experimentally assessed. The experimental results show that by employing the dv/dt filter in SiC-based adjustable speed drives, the motor overvoltage can be reduced from 1.95 pu to 1.17 pu. Moreover, for a given cable-fed motor drive system, increasing the filter inductance can reduce the filter current and power loss in damping resistors. However, the impedance of the filter at its resonant frequency should be less than that of the cable to avoid the unexpected overvoltage oscillations.