Enhanced control strategy for MMC-based STATCOM for unbalanced load compensation

Modular Multilevel Converters (MMC) technology is today one of the preferred technology in HVDC and large STATCOM applications due to modularity, fault tolerance and high efficiency, but the voltage balancing becomes very challenging, especially during negative sequence current injection as required for load unbalance compensation. This paper proposes an improved balancing strategy for the delta configuration to overcome this situation based on the injection of a third harmonic zero sequence current. Simulation results have proved the effectiveness of the proposal even where different switching losses and capacitor tolerance are taken in consideration.