A sliding mode control technique for a modular transformerless HVDC conversion system

This paper presents a non linear control technique, based on the sliding mode theory, for a modular series cascade HVDC conversion topology. The proposed control technique exhibits bidirectional power flow, minimum line input current THD factor, unity input true power factor, minimum ripple at the DC side and robust performance at transient conditions. The above mentioned advantages are equally achieved under variation of DC voltage and load. Moreover such a technique does not require neither phase shift transformers at the grid side, nor input harmonic filters. The feasibility and robustness of the technique introduced is demonstrated by implementation results of a prototype construction concerning load sudden changes and voltage dips.