Unbalanced power control of a modular multilevel converter with photovoltaic resources and the capacitor voltage ripple analysis

The modular multilevel photovoltaic (PV) converter can achieve independent power control and help to increase the efficiency of the system. However, the output power among PV modules is unbalanced, which will result in the power loss of system if not properly controlled. This paper first introduces a power control scheme to adjust the power distribution among dc grid, ac grid and PV modules, and presents the mathematical bases of the scheme and the unbalanced power control of the strategy. However, the voltage ripple of MMC sub module (SM) capacitor is also an important parameter. In this system, the SM voltage ripple has not been analysed in relevant articles. Because there are many variables, it is not easy to analyse. Here, the voltage ripple law of the SM capacitor is analysed, by simplifying variables and presenting a fast analytical method, which has reference significance for the selection of SM capacitor. Matlab simulation and the hardware in the loop simulation experiment built by StarSim of Modelling Tech verify the effectiveness of the introduced control strategy and the correctness of the SM capacitor ripple analysis.