Analysis and calculation of the power device switching frequency of modular multilevel converters

In order to analyze and calculate the switching frequency of power switches in modular multilevel converter (MMC) quantitatively, a mathematical model for sinusoidal pulse width modulation (SPWM) and nearest level modulation (NLM) is proposed in this paper. The factors influencing the switching frequency are summarized, and the superior and inferior limits in extreme cases of operation are analyzed which infer the range of switching frequency. And then, the theoretical formulae for calculating the switching frequency are presented, which is helpful for designing the parameters of the power switches and the control system. Finally, the correctness of the calculation formulae and the feasibility of the analysis are well validated by simulation results.