Forced Commutated HVDC Converters

Since the implementation of the first HVDC thyristor valve at Eel River (Canada) in the early 1970’s, HVDC transmission has experienced tremendous growth. As power systems grow and become more integrated, interconnections to neighboring ac systems are becoming increasingly necessary to enhance stability, security of supply, flexibility and for other economic benefits. Primarily for stability reasons, the trend is for such interconnections to be asynchronous HVDC ties. And usually these interconnections feed into locations where the ac power systems are weak. Utility system planners realized that the critical element in the HVDC inter-tie was the thyristor converter, which has a fundamental limitation that it requires a reliable and adequately stiff voltage source for valve commutation purposes.