A Carrier-Based Discontinuous Space-Vector PWM for Common-Mode Voltage Reduction in Dual-Input Three-Level T-Type Inverters With Unbalanced Neutral-Point Voltages

With unbalanced neutral-point (NP) voltages, the common-mode voltage (CMV) will be increased in dual-input three-level (3L) T-type inverters. Therefore, in this article, a novel discontinuous space-vector pulsewidth modulation for CMV reduction (RCMV-DSVPWM) is proposed. First, the CMV of vectors is analyzed considering unbalanced NP voltages. New space vector diagrams are obtained by abandoning vectors with high CMV, where the nearest three vectors are selected to synthesize the reference vector for reducing output current harmonics. Afterward, subsector divisions and vector sequences are optimized to suppress the CMV and switching losses. Then, to further reduce the computation burden, a cutting-line method is designed for the subsector judgment, and the modulation waves are analytically derived for the carrier-based implementation. Finally, the proposed RCMV-DSVPWM is verified through comparative simulations and experiments under unbalanced NP voltages, where the CMV is effectively suppressed with high efficiencies and low current harmonics.