DC-link voltage control strategy for an NPC voltage source converters in an effective energy storage system

The paper discusses an issue of the voltage balancing in the intermediate DC circuit of a three-level converter system for a smart grid application. A combination of two methods of the voltage balancing is presented in the paper. The voltages of DC-link capacitors, depending on the operating mode, are controlled by the three-level grid connected AC/DC converter or by the two level DC/DC converter and additional balancer circuit. In order to verify the proposed method for the DC-link voltage control, a simulation and an experimental studies have been executed.