Mitigation of Uneven Overvoltage Distribution in Motor Windings Fed by SiC-Based Drives Using a GaN-Based Adaptive Surge Impedance Method

This paper investigates the overvoltage spikes in motor drive systems caused by fast-switching transistors, e.g. SiC-MOSFETs. These fast-switching devices produce high-frequency overvoltage spikes that are unevenly distributed across the stator windings, resulting in non-uniform stress on the windings’ insulation. This uneven stress arises from higher leakage currents in the first turns and coil, attributed to stray capacitances between the stator windings and the motor frame. Therefore, the most significant overvoltage stress occurs in the first coil, which is located closest to the motor terminals. Such stress can cause insulation breakdown and inter-turn short-circuit faults. To address this, the paper discusses an adaptive surge impedance technique, aimed at reducing stress in the first coil of each phase. This technique employs a parallel circuit incorporating an analog voltage sensor for detecting overvoltage onset and a GaN transistor, paired in series with a ceramic capacitor. This setup specifically targets high-frequency currents, thereby having no impact on the motor’s torque profile. Given the high-temperature robustness of GaN components and the reliability of ceramic capacitors, particularly in the pico-farad range, this solution ensures that the motor’s standard operations remain unaffected by potential component failures. Furthermore, experimental testing has demonstrated that this method mitigates the uneven distribution of high-frequency overvoltage stress across the stator windings, thereby enhancing overall system reliability.