Protection of permanent faults on DC overhead lines in hybrid converter based HVDC system

Due to the popularity of power electronics devices HVDC system becomes potential candidate for grid integration of renewable energy over long transmission. The paper presents hybrid multilevel converter (HMC), which is one of the most suitable replacement for traditional voltage source converters because of fast response during dc link fault on overhead lines. HMC consists of two main parts, one which is director switches (DSs) made from number of series insulated-gate-bipolar-transistors (IGBTs) and second one is wave shaping circuit (WSC) consists of stack of full-bridge sub modules (FSMs). This paper mainly focuses on the modulation techniques and control for the DSs and WSCs. To determine the number of FSM to be inserted, nearest level control (NLC) method is used in this paper. Third harmonic injection and sorting method also discussed for the capacitor voltage balancing. Current and voltage waveforms under normal condition and dc fault condition are analyzed by using MATLAB simulation.