Analysis and Mitigation of the Common-Mode Noise in a Three-Phase SiC-Based Brushless DC Motor Drive With 120° Conduction Mode

The generation and propagation of the common-mode (CM) noise depends on the pulsewidth modulation (PWM) technique, parasitic capacitances, and rate of change of voltages imposed on the motor. In the literature, the CM noise analysis of the brushless dc (BLdc) drive operated with 120^\circ conduction mode is reported neglecting the impact of the floating phase, and the analysis is restricted to low-voltage silicon-based drives. In this article, an in-depth theoretical analysis of the CM noise in the BLdc drive is presented considering two commonly used schemes in 120^\circ conduction mode: six-step commutation and bipolar PWM. It is proven through experiments that the impact of the floating phase cannot be neglected especially with the high-voltage slew rate imposed by silicon carbide (SiC)-based inverters on the drives. By considering the impact of the floating phase, the CM noise in the BLdc drive is modeled through mathematical equations, and suitable equivalent circuits are presented. Finally, a step-by-step design procedure of the CM filter for the BLdc drive is presented. Experimental results on a three-phase star-connected SiC-based BLdc drive are provided to substantiate the analysis and CM filter design.