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

Modular multilevel converters have become widely used in HVDC applications due to easy scalability and near sinusoidal output voltage synthesis. It is made up of an array of submodules comprising of semiconductor switches and floating capacitors. An important challenge in these multilevel topologies is voltage balancing of the floating capacitors. A voltage balancing technique has been proposed for a modular converter with 3-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 2/3^rd of the switching transitions to be soft switched. The proposed control is validated by simulations in MATLAB/Simulink.