Mitigation of Motor Reflected Overvoltage Fed by SiC Drives—A New Solution Based on Smart Coils

Abstract

While wide bandgap (WBG) switches have revolutionized power electronics and motor-drive systems, the high $dv/dt$ associated with these fast-switching semiconductors can easily induce reflected high-frequency overvoltage spikes on motor stator terminals. The shorter rise time of the voltage pulses confines the cable length between the inverter and the motor in practice to avoid overvoltage across the motor stator windings. Even with shorter cables, voltage spikes from variable-speed drives can still cause premature insulation failure and reduce the remaining useful lifetime of the motors. While effective, conventional methods such as $dv/dt$ passive filters or active gate drivers are usually bulky and/or inefficient. To address this problem, an overvoltage mitigation solution, named “Smart Coil,” is introduced in this article. The smart coil circuit is installed in parallel with the first coil of each motor phase, which typically experiences the highest reflected overvoltage. Upon detection of overvoltage, the proposed ultracompact smart coil circuit, located at the motor junction box, is activated to limit voltage stress across the coils. Since the smart coil is connected in parallel with the first coil, it only needs to process very low pulsed power during the overvoltage transients. Therefore, it has high efficiency and an ultracompact footprint while effectively mitigating voltage spikes. The proposed smart coil circuit can be easily scaled for various motor-drive systems regardless of the cable length or rise time of the switching devices. Simulation and experimental test results are provided to verify the effectiveness of the proposed method.