A General Modulation Strategy for Suppressing Common-mode Noise of Odds Multilevel Converter

Multilevel converters have promising prospects in medium-voltage and high-voltage applications, but the common-mode voltage (CMV) generated by multilevel converters is still a crucial problem. Besides, the mainstream modulation methods based on space voltage vectors to eliminate CMV are complicated and non-universal, especially for the converters with many levels. Therefore, this paper proposed a generalized technical solution based on level-shifted carriers to eliminate the CMV caused by modulation, which was simple and versatile for any multilevel converters configured with odd voltage levels. For a (2N+1)-level converter, the three-phase voltage references from controller were linearly transformed into three pseudo references, which were compared with N level-shifted carriers to obtain three pseudo PWM signals. The final three-phase PWM signals were obtained by subtraction in pairs among the three pseudo PWM signals, and it was the subtraction in pairs of the pseudo signals that ensured the elimination of CMV. The proposed technical solution only needs the simple process of carrier comparison and four fundamental rules instead of the complicated procedure including the selection and synthesis of voltage vectors. Relevant experiments are performed on a multilevel prototype that is configured as 5-level, 7-level and 9-level converters to validate the proposed method. © 2022 Chin.Soc.for Elec.Eng.