IEEE Transactions on Power Delivery Special Section on “Frontiers of DC technology” DC technology for power delivery has experienced rapid development in the last 10-20 years, in terms of new converter topologies, new apparatus, increased power ratings, improved performance/reliability, modularity and size reduction. In the same period, the demand for DC technology has perhaps increased even more, driven by the need for integration of large remote offshore/onshore renewable energy sources, demand for controllable power flows in lines because of market-based grid planning and power trading, increasing demand for cable-based transmission, desire to operate weak AC grids at higher loadings, requirements for more national/international interconnectors in particular at very high ratings, and general load increase. At present, it is widely believed that complex and interconnected DC power grids could be built with comparable performance, reliability, flexibility and losses as traditional AC grids. The introduction of Voltage Sourced Converter (VSC) technology using Modular Multilevel Converter (MMC) topologies opens the prospect of significantly increased ratings of DC technologies at acceptable losses/size and many new converter functions/roles in DC systems. There is substantial ongoing research and development worldwide on challenges in various DC apparatus, on DC system operation, control and protection, on topics related to DC modelling and simulation, but also on standardisation, interoperability, testing and other aspects. These topics require considerable advances in technology and in many aspects fundamentally different approaches from traditional practices and technologies with AC systems. This Special Section aims to promote research, innovation and exchange of information related to the key challenges which will shape the development of HV and MV DC power delivery. The topics of interest of this Special Section are within the traditional IEEE TPWRD scope (http://sites.ieee.org/tpwrd/) related to DC technologies, and in particular: 1. Architectures of HV and MV DC Grids and hybrid AC-DC grids, 2. Converter technologies, VSC - MMC half-bridge, full-bridge and hybrid converters, LCC converters, DC/DC converters for MV and HV DC grids, 3. DC system protection and grounding, DC fault management, DC grid fault detection and discrimination Overvoltage management and grounding aspects of DC systems, 4. DC circuit breakers, fault current limiters and switchgear, Mechanical and semiconductor DC Circuit breakers, DC fast acting disconnectors, GIS DC switchgear, Superconducting and other DC fault current limiting devices, 5. Substations, cables, transducers, electrodes, surge arresters, filters …. for DC systems, 6. Modelling and simulation of electromagnetic transients in DC systems, Analytical modelling, Simulation of DC systems including DC faults, Real time simulation, 7. Challenges and solutions of integrating AC and DC systems (apparatus perspective), Power flow, voltage and frequency support, ancillary services provision, Operation, dynamics and control, Harmonic distortion, Stability, AC to DC and DC to AC interactions 8. Standards, interoperability and multi-vendor issues, 9. Demonstration and laboratory projects, It is noted that LV DC systems are not in the scope of this Special Section. SUBMISSION GUIDELINES This Special Section solicits original work that is not under consideration for publication in other venues. There is no need for the submission of an extended abstract. Please submit the full paper directly. Authors should refer to: http://sites.ieee.org/tpwrd/ for information about requirements, formatting and the website of submission. When submitting, please select the submission type “Frontiers of DC technology.” Any changes on deadlines or other updates related to this Special Section will be announced in the “Call for Paper & News” section of the above website. IMPORTANT DATES September, 2016: Call for papers issued, January 31, 2017: Deadline for submission of full papers (early submission is recommended), July 31, 2017: Notification of final decisions, December 2017, Publication of Special Section, GUEST EDITORIAL BOARD FOR THE SPECIAL SECTION Dragan Jovcic (Guest Editor-In Chief), University of Aberdeen, UK, Nilanjan Ray Chaudhuri, Pennsylvania State University, USA, Sebastien Dennetiere, RTE, France, Oriol Gomis-Bellmunt, Technical University of Catalonia, UPC, Spain, Reza Iravani, Univerity of Toronto, Canada, Norman MacLeod, WSP | Parsons Brinckerhoff, UK, Liangzhong Yao, China Electric Power Research Institute, China, Rong Zeng, Tsinghua University, China, EDITOR-IN-CHIEF Wilsun Xu, IEEE Transactions on Power Delivery