Analysis and calculation on switching frequency and switching losses of modular multilevel converter with maximum sub-module capacitor voltage deviation

Abstract

To reduce switching frequency of modular multilevel converter (MMC), proper sub-module (SM) capacitor voltage deviations would be allowed in the nearest level control. This study proposes a new method to evaluate the switching frequency and switching losses of MMC with maximum SM capacitor voltage deviation. Switching transitions are presented and then the analytic equations of switching frequency and switching losses are derived based on the definite integration approximate substitution. The factors affecting the switching frequency and losses are summarised. Besides, this study analyses the range of maximum SM capacitor voltage deviation as well. The accuracy of this method is proved by a 46-level single-phase MMC under different operating conditions in MATLAB/Simulink. Finally, a 9-level single-phase MMC laboratory prototype is also built to validate this method.