Comparative Research on Common-mode Voltage of T-type Three-level Converter Caused by Modulation Strategy

In this paper, the cause and calculation formulas of common-mode voltage of T-type three-level converter were introduced, then the common-mode voltage caused by traditional SPWM, SVPWM and two improved modulation strategies were compared. Through the comparisons in this article, it found that the improved modulation strategies have lower common-mode voltage compared with the traditional SPWM and SVPWM strategies. In order to eliminate the common-mode voltage completely, a modulation wave phase shifted PWM strategy was proposed. It has been proved that the common-mode voltage was eliminated completely under the new modulation strategy, but the THD of line voltage was also increased. Finally, all of the modulation strategies were simulated and verfied in Matlab/Simulink.