Evaluation of machine neutral point overvoltage mitigation in SiC motor drives using three passive filter designs

In SiC inverter-fed motor drives, fast-switched power devices escalate the reflected wave phenomenon, causing overvoltage oscillations at the motor terminals with shorter cable lengths between the inverter and motor. Likewise, overvoltage oscillations manifest at motor neutral point due to the reflection of inverter common-mode voltage through the machine windings. Despite extensive research on motor terminal overvoltage mitigation, the motor neutral point overvoltage remains insufficiently addressed in the literature, although it can have a more detrimental impact on the machine winding insulation especially if the high switching frequency of SiC inverters aligns with the machine antiresonance frequency. This paper evaluates the effectiveness of three passive filter designs (R, RC, and C filter) connected between the motor neutral point and grounded frame for neutral point overvoltage mitigation. The paper provides mathematical design guidelines for the parameter selection of the three filters while assesses their performance in mitigating the motor neutral point overvoltage. An experimental evaluation using a 2.2kW SiC-based motor drive setup is presented, demonstrating the effectiveness of the three filter designs to eliminate the motor neutral point overvoltage while highlighting the pros and cons of each filter design.