Control strategies for capacitor voltage balancing in modular multilevel converters

Different schemes of modified conventional sorting algorithms with low complexity are proposed in order to balance the voltages of submodule (SM) capacitors for the modular multilevel converter (MMC). Two different procedures are investigated in this study. The main idea is to achieve voltage balance within the MMC arms with fewer current sensors. The two different methods are examined under different operating conditions; for instance, with a sudden change in the DC-source or when different load values are applied. The advantage of such sensor-less control methods is to simplify hardware communications in general. Moreover, the reliability of the MMC is also improved. Simulation analyses of a single-phase four-level MMC are conducted to show the effectiveness of the proposed methods.