Analysis and Mitigation of Common-Mode Noise With Different Modulation Strategies in SiC-Fed Three-Phase Brushless DC Motor Drive

Pulsewidth modulation (PWM) strategies for brushless dc (BLdc) drives, namely, unipolar and bipolar schemes, focus on optimizing torque ripple, efficiency, or vibration performance. Adoption of wide bandgap (WBG) devices such as silicon carbide (SiC) for high-voltage BLdc drives has further improved the efficiency and power density of the drive; however, the critical issue of common-mode (CM) noise in such drives is seldom investigated. Therefore, the impact of two classes of PWM schemes in 120 degrees conduction mode, namely: 1) unipolar and 2) bipolar PWM schemes on the CM voltage, is investigated in this article. First, a generalized mathematical expression for CM voltage is derived and validated through experiments for various PWM schemes in a BLdc drive. Furthermore, the impact of CM voltage on CM current is thoroughly analyzed for 10- and 100-kHz switching frequencies. The CM choke requirements with bipolar and unipolar PWM schemes for different switching frequencies are compared. Finally, the theoretical analysis is substantiated by the experimental results on a 1.5-kW, 310-V SiC-fed BLdc drive.