Common-Mode Voltage Mitigation in 3-Phase 3-Level VSI with Dc-bus Midpoint Switching

Common Mode voltage (CMV) is the prime source of EMI issues in 3-phase electric drives. Different approaches to reduce the CMV are reported in the literature. In this paper a simple and effective switching scheme for 3-phase, 3-level inverters is proposed to mitigate the CMV. In the proposed method, a new topology for 3-level inverters with multiple DC bus capacitors is presented and the proposed switching scheme results in zero CMV with suitable switching of DC bus mid-point for each switching state. Available methods in literature for CMV reduction use modified PWM switching schemes [3], [4], which are suffering from poor THD of voltage waveform. Proposed switching scheme leads to zero CMV without compromising with the quality of the voltage waveform.