Back-to-Back Modular Multilevel Converter for drive applications under unbalanced grid conditions

In this paper, a control system for a Back-to-Back Modular Multilevel Converter based drive is proposed. The control system is able to operate either in balanced and unbalanced grid-conditions by regulating the power oscillations choosing an appropriate circulating current reference. Unity power factor operation (for balanced grid), reduced harmonic distortion, capacitor voltage balance and bidirectional power flow are feasible with the proposed methodology. Simulations and experimental results obtained with a 7.5-kW 30 power cells prototype are presented to validate the effectiveness of the proposed control system.