Power Flow Control using Modular Multilevel Converter for 3-phase AC/AC Conversion

Modular multilevel converter (MMC) has been demandable to the researcher for its scalability and high voltage capability with low harmonic content. Having a completely modular design with cascaded full-bridge cells, MMC can reduce semiconductor losses. The transformer-less MMC is to realize lightweight and downsizing with the attractive performance for high-voltage, high-power conversion and also more helpful for the reduction of global warming. At the time of operation, it is very important to control input and output current, output voltage, circulating current and capacitor voltage. Average control and voltage balancing of the capacitor is important for improving the stability and controllability. The control scheme is explained for grid-connected three-phase MMC. The effectiveness is verified by the proposed control method in some typical conditions.