Common-Mode Choke Design to Eliminate Electrostatic Discharge Machining Bearing Currents in Wide-Bandgap Inverter-Fed Motor Drives

The electrification of mobility sectors, including automotive, aerospace, and robotics, has accelerated the need for compact and high-efficiency power converters in electric motor drives. Wide-bandgap (WBG) semiconductor–based inverters offer significant advantages over conventional silicon IGBT inverters by enabling higher switching speeds, elevated switching frequencies, and improved power conversion efficiency. However, the adoption of high-frequency switching introduces several challenges, particularly increased motor neutral point voltage stress, originating from inverter common-mode (CM) voltage. The increased neutral point voltage directly elevates motor bearing voltage, the primary driver of motor bearing currents, among which electrostatic discharge machining (EDM) bearing current is the primary cause of bearing degradation in low-power motors. This paper experimentally investigates the root causes of the EDM phenomenon and identifies the key factors influencing its occurrence and severity in WBG-based drive systems. The conventional CM choke designs effectively attenuate motor CM currents and EMI; however, they are ineffective in suppressing EDM bearing currents. In this paper, an alternative CM choke design methodology is proposed to eliminate EDM bearing currents by optimizing the choke inductance to shift the motor CM antiresonance frequency below the inverter switching frequency, thereby ensuring that nearly all source CM voltage is absorbed by the choke. This design approach effectively minimizes the voltage appearing at the motor neutral point and across the bearings, thereby suppressing EDM bearing current spikes without affecting motor DM performance. The choke parameters are mathematically derived for optimal performance and validated through experimental testing on a 2.2 kW three-phase star-connected induction motor powered by a wide-bandgap two-level voltage-source inverter.