Comparative Analysis of Two-Phase and Three-Phase Common-Mode Equivalent Circuit for Three-Phase Brushless DC Motor Drive

Common-mode (CM) equivalent circuit plays a critical role in understanding noise propagation path and devising suitable measurement and mitigation schemes in industrial drives. A two phase CM equivalent circuit is commonly used for studying the electromagnetic interference (EMI) issues in three-phase brushless dc (BLdc) motor drives. Recent studies on SiC-fed high-voltage BLdc drives show that the mutual coupling between the floating and conducting phases also contributions to the CM noise. However, the impact of neglecting the floating phase in CM analysis is not quantified. Therefore, a comparative analysis of two-phase and three-phase CM equivalent circuits is presented in this paper considering high-voltage drives. Through experiments on a 310 V, 1.5 kV SiC-fed three-phase BLdc drive, it is shown that using a two-phase equivalent circuit will significant underestimate the CM noise.