Experimental verification of hexagonal modular multilevel converter for 3-phase system

The modular multilevel converter (MMC) with cascaded full bridge cells is available for a utility interactive inverter and AC/AC transmission system without transformers in high voltage line. When it is interconnected with power line, it is possible to control the active power flow in order to supply or charge the power in the line. This research applied a Hexagonal type MMC (H-MMC) to 3-phase AC-AC conversion system. The H-MMC has six arm modules with floating capacitors, which are connected in a shape of hexagon. It is required to regulate input power, output power and floating capacitor voltages by controlling currents in arm modules. These currents can be controlled by internal model principle and H-MMC can operate reliably. Theory of H-MMC control is explained and the operation is performed in simulation and experiment. Effectiveness of the proposed control method in some typical conditions is verified in experiment.