Space Vector Modulation Strategy for Common-Mode Voltage Suppression in the Reduced Switch Count Three-Level Inverter With Unbalanced Neutral-Point Voltages

The reduced switch count three-level inverter (RSC TLI) has been proposed to save the system cost of the conventional three-level inverter. In some special applications, the RSC TLI should be operated with simultaneous lower common-mode voltage (CMV) and unbalanced neutral-point voltage (NPV) conditions. For this reason, this article further proposes a space vector modulation (SVM) strategy that fulfills the above requirements. First, the basic vectors with low CMV amplitudes are selected, and four basic vectors are employed to synthesize the reference vector and achieve NPV flexible control. The duty cycles of the employed basic vectors are obtained by a novel indirect method, and the appropriate switching sequences are designed to further reduce the current harmonic and keep lower switching losses. Finally, the separate control of capacitor voltages is achieved by using a closed-loop control approach to optimally regulate the duty cycles of different basic vectors. Compared with the conventional strategy, the proposed scheme can reduce the CMV magnitude by half and is applicable to unbalanced NPV conditions. The feasibility and effectiveness are verified by experiments.