A voltage level based predictive direct power control for modular multilevel converter

This paper proposes a novel voltage level-based predictive direct power control (PDPC) strategy integrated with voltage sorting algorithm for a three phase grid-connected modular multilevel converter (MMC). The main advantage of the proposed control strategy, compared with the predictive current controllers, is that it does not need angular information of grid parameters. Therefore, it is simpler and able to get rid of rotary transformation and inner current loop. Contrary to the phase-by-phase control in predictive current controllers, the proposed control scheme advocates three-phase control. As a result, it achieves significant improvement in terms of smaller power ripples, more accurate tracking of power references, and less current harmonics. Further study reveals that the proposed voltage level-based PDPC exhibits less switching frequency irrespective of the magnitude of power references and power angles. Meanwhile, the capability of capacitor voltage balancing control and circulating current control in the proposed PDPC is as good as in the predictive current controllers. Some in-depth simulation comparisons with one of the existing predictive current controllers are given to validate the effectiveness of the proposed strategy.