High-Frequency Motor Impedance Analysis and CM Current Estimation of Electric Motors With Concentrated and Toroidal Windings

The rising demand for wide bandgap (WBG) devices and the growing need for compact motor drives in electric vehicles (EVs) have escalated the challenges associated with common-mode (CM) current and electromagnetic interference (EMI) in EV motor drives. This article investigates the impact of concentrated winding (CW) and toroidal windings (TWs) on motor CM current. The prototype CW and TW motors are analyzed, and dominant winding-to-ground capacitances are identified. High-frequency (HF) motor CM impedance models up to 30 MHz are developed for the prototype CW and TW motors and are used to estimate the CM current in motors. The simulation and experimental results reveal that TW substantially increases the CM capacitance in the motor, increasing the motor CM current to about 10 times higher than the CW motor. Analytical expressions for the dominant CM capacitances are derived from the general CW and TW structure with different motor geometries. These analytical models confirm that a TW motor will have higher CM capacitance than the comparable CW motor as the outer diameter of the motor increases. This analytical study generalizes the critical findings from comparing the prototype CW and TW motors for extended applications with higher power and speed.