SUMMARYThis paper discusses the present and future power conversion systems for high voltage direct current transmission systems. It begins with an introduction into the commercially available semiconductor switching devices and future wide bandgap devices specifically silicon carbide devices. Different High Voltage Direct Current (HVDC) system configurations including the point‐to‐point, back‐to‐back, multi‐terminal, and hybrid ac and dc are discussed. Different configurations of the current source and voltage source converters are presented, and the concept of redundancy and availability for the current source and voltage source schemes is elaborated on. The most significant trends in dc power systems including the transformerless HVDC, ultra high voltage dc transmission, ac to dc replacement, tripole HVDC, dc grids, dc circuit breakers, and dc transformers are presented. Copyright © 2011 John Wiley & Sons, Ltd.