The inherent neutral-point (NP) voltage fluctuation of Vienna rectifier could have side effects on the input current quality. However, such effects have not been thoroughly analyzed in the literature yet. In this paper, based on the three-level to two-level space vector modulation (SVM) transformation, a novel method to evaluate the influence of the NP voltage fluctuation on the input current quality is introduced, which could optimize the NP control parameters. The proposed method superimposes the NP voltage fluctuation on the basis vectors, thereby establishing the correlation between the NP voltage fluctuation and the square root mean square (S-RMS) of the input current ripple. The detailed model of the NP oscillation under two-level coordinates is presented. By combining the two-level modulation, NP voltage hysteresis control is adopted to simplify neutral point voltage control and suppress NP low-frequency oscillation. Comprehensive influence of the NP compensation coefficient on the input current quality under NP hysteresis control is obtained, and the hysteresis control parameters are optimized by using the proposed evaluation method. Simulation and experimental results verify the correctness and effectiveness of the proposed evaluation method.

A novel three-phase switched-capacitor multilevel inverter (SCMLI) with reduced capacitance and balanced neutral-point voltage is proposed in this paper. Applying only one DC source, the three-phase seven-level topology possessing voltage-boosting capability is accomplished without the high-voltage stress of power switches. Owing to the inherent redundant switching states of the proposed topology, two charging approaches that can effectively limit the voltage ripples and path selection for capacitors can be realized. This provides the presented topology with reduced capacitance, balanced neutral-point voltage, good performance in not only the three-phase four-wire system but also the three-phase three-wire system, and low total harmonic distortion (THD) of the output voltage. A comprehensive comparison with previous SCMLIs in various aspects is conducted to validate the merits mentioned above. The simulation results accord with theoretical analyses, confirming the feasibility of the proposed three-phase SCMLI.