A Generalized Modulation Method for Common-Mode Voltage Reduction of Dual-Input Three-Level Inverter

The dual-input three-level inverter should have the ability to operate in certain areas where the dc-links are unbalanced. This paper proposes a generalized large-medium-zero space vector modulation (GLMZ-SVM) method to obtain high-quality output currents and suppress common-mode voltage (CMV) amplitude simultaneously when the dc-links are unbalanced. In this method, a modified space voltage vector diagram (MSVVD) based on the unbalancing factor is obtained, which is highly asymmetrical compared to the space vector diagram when the dc-links are balanced. Then, a novel sector division method of MSVVD is presented by six medium vectors and six large vectors. In each sector, the large, medium, and zero vectors are used to synthesize the reference voltage vector to reduce the CMV amplitude. The duty cycles of large, medium and zero vectors are calculated based on the modified volt-second balance principle with the unbalancing factor. To further reduce harmonics and avoid switching losses between switching cycles, a symmetrical five-segment switching sequence is designed. Comparisons with conventional methods show that the CMV amplitude of the proposed method is reduced by half and the high-quality output currents are obtained. Both simulation and experimental results validate the correctness of the theoretical analyses and the effectiveness of the proposed scheme.