Improved Modulation Strategies of MMC for Increasing Voltage Level

Abstract

Due to the modularity, reliability and robustness of the modular multilevel converter (MMC), it is considered as an effective and suitable converter in high voltage direct current (HVDC) applications. However, it also increased the complexity of its modulation strategy because of the capacitor voltage balancing. In this paper, a decimal pulse width modulation (DPWM) is introduced. Then we proposed two improved DPWM (IDPWM) methods which can be almost two-fold increase in the number of voltage levels by modifying the phase difference of triangular carrier between upper and lower arm, and improving the judging criteria of the DPWM method. Also, the capacitor voltage balancing method which is suitable for the IDPWM is given. Performance of the proposed improved DPWM methods and the DPWM method for a MMC unit was evaluated in the MATLAB/SIMULIKN. The simulation results indicated that the improved DPWM methods can achieve a lower harmonic distortion.