Ship to Grid: Medium-Voltage DC Concepts in Theory and Practice

Abstract

C Corporate researCh Centers, universities, power equipment vendors, end users, and other market participants around the world are beginning to explore and consider the use of dc in future transmission and distribution system applications. recent developments and trends in electric power consumption indicate an increasing use of dc-based power and constantpower loads. in addition, growth in renewable energy resources requires dc interfaces for optimal integration. a strong case is being made for intermeshed ac and dc networks, with new concepts emerging at the medium-voltage (mv) level for mvdc infrastructure developments.at the turn of the 20th century, the use of ac transmission, as opposed to dc, was a justifiable decision for many reasons. Looking toward the future of transmission and distribution, this decision must be reevaluated in light of the changes taking place throughout the u.s. electric grid at all levels: generation, transmission, distribution, and end use. in 2006, electric power research institute (epri) presented a number of valid arguments that strengthened the case for dc infrastructure in the 21st century. modern advances in the transportation industry have often come through the application of electronics (electric vehicles and magnetic levitation trains, for example). these innovations utilize dc power, requiring an ac-to-dc conversion within the current grid infrastructure. the microgrid, composed of distributed generation (such as photovoltaic systems) and energy storage systems that produce dc power, is a key emerging technology. Finally, utilities are trying to develop solutions for integrating renewable energy with storage devices to deliver dc power. these advances will make utility-scale energy storage more economical and efficient.power electronics technology is an efficient, powerful, and reliable solution for integrating large amounts of renewable generation into existing grid infrastructure. increased renewable integration with aggressive growth targets is a mandate set forth by the u.s. government, with a deadline in 2030. developments in the area of power electronics, including the application of novel semiconductor devices and materials, have unlocked the potential for higher-capacity, faster-switching, lower-loss conversion, inversion, and rectification devices. in recent years, the advent of silicon carbide solid-state electronic devices, which have lower switching and conduction losses compared with silicon devices, has made dc-ac conversion more promising in the near-term time frame. virtually all voltage and current ratings are possible by utilizing series and parallel combinations of discrete semiconductors. all of these factors are combining to form an opportunity for the development and further deployment of dc technology throughout the electric grid at all levels.

Past, Present, and Future Challenges of the Marine Vessel’s Electrical Power System

“…One of the reasons for this was that the early dc systems (without power electronics) needed rotating devices to transform the power from one voltage level to another [23]. The ac power system has been the most used power system in marine vessels, but now, with modern power electronics and other technological advantages, the discussion of using dc or ac distribution in shipboard power systems has been brought to the table and some of the key points whether to use ac or medium-voltage dc (MVdc) are (adopted from [20], [24]- [26]):…”

Power Quality in DC Power Distribution Systems and Microgrids

“…With many global research efforts focusing on DC microgrids [40,41], development of high power topologies for DC-DC converters to serve as the interfacing entity between grid and load still requires increased investigation. In particular, novel applications of multiple input multiple output (MIMO) converters have been suggested to achieve a good compromise between high availability and reduced costs [21].…”

Multi-terminal DC grids: challenges and prospects

“…DC technology has entered a new Renaissance period in recent decades, several generations after Edison and Westinghouse's public battles facing DC versus AC in the famous ''war of currents'', back by 1880 [1]. In the late 19th century, AC came to dominate power transmission design, as AC transformers offered a cost efficient solution to the problem of transferring bulk power from centralized power stations over long distances.…”