Direct Current (DC) transmission and distribution technologies have evolved in recent years. They offer superior efficiency, current carrying capacity, and response times as compared to conventional AC systems. Further, substantial advantages are their natural interface with many types of renewable energy resources, such as photovoltaic systems and battery energy storage systems at relatively high voltage, and compliance with consumer electronics at lower voltages, say, within a household environment. One of the core building blocks of DC-based technologies, especially at medium voltage levels, is power electronic systems technology. This cannot be emphasized enough as these units process, convert, and regulate all DC power and provide intelligence and sensing as electric power grids evolve. These advantages have led to a rise in the utilization and applications of DC in modern power systems. This includes high voltage DC transmission systems, DC distribution grids, DC microgrids, electric vehicle charging infrastructure, and the maritime industry. However, there are still substantial challenges to the operation of these systems. Examples include a lack of standards for DC based power infrastructure and DC system protection. This book presents the state of the art in medium voltage DC systems research and development, covering grid architecture, power converter design, transformers, control and protection for both traditional and mobile DC applications such as all-electric ships. This text, the first of its kind, provides essential information for researchers and research-oriented engineers working for academia, a manufacturer or utility, who wish to broaden or update their knowledge of medium voltage DC systems and associated equipment.