Capacitor voltage balancing and an intelligent commutation technique in a new modular multi-level converter-based HVDC system

Modular multi-level converters have become widely used in HVDC applications due to their easy scalability and near-sinusoidal output voltage synthesis. They are made up of an array of submodules comprising semiconductor switches and floating capacitors. An important challenge in these multi-level topologies is voltage balancing of the floating capacitors. A voltage-balancing technique has been proposed for a modular converter with three-level submodules. This new converter submodule topology results in added benefits over conventional existing half-bridge submodule topologies. An intelligent commutation technique is proposed which results in two-thirds of the switching transitions being soft-switched. The proposed control is validated by simulations in MATLAB/Simulink.