Fundamental Frequency Sorting Strategy for Capacitor Voltage Balance of Modular Multilevel Converters with Phase Disposition PWM

Modular multilevel converters (MMCs) become more and more attractive in high-voltage and high-power applications. The balance of the floating capacitor voltages is vital for MMCs. In order to balance the capacitor voltages, a fundamental frequency sorting strategy with Phase Disposition PWM is proposed in this paper. A dual sorting method, which sorts the capacitor voltage increments and the present capacitor voltages simultaneously, is implemented to change the relationship between the carriers and the sub-modules once in every fundamental period. Due to the low sorting frequency, the intensive computation of the controllers is avoided. Moreover, the switching commutations are evenly distributed among the power devices. Furthermore, the measurement of the arm current is eliminated, which further simplifies the communication among different controllers. Finally, the proposed voltage balance strategy is validated by simulation and experiment.