HVDC Transmission Systems and DC Grids: Developments and Challenges

Abstract: As large renewable power plants tend to be located far from consumption centers, integration of the power collected from these power plants represent a major challenge. For example, the electrical outputs of these renewable power plants could be DC or AC voltage with magnitude and frequency which are incompatible with that of the AC grids. Therefore, power electronic interfacing is needed to decouple the AC grids from the power plants, control active and power exchange with AC grid, and assist renewable power plants to ride-through different AC and DC network faults. The commercially available state-of-the-arts high voltage direct current (HVDC) link technologies are based on voltage source converters. However, most of the presently operational HVDC transmission systems are based on the thyristor line commutated current source converter technology that offers low semiconductor power loss and high power density, thanks to the robustness and high current capability of the thyristor in a single wafer capsules. On the other hand, thyristors inject significant low frequency harmonics into AC side, which must be eliminated by large passive filtering, and cannot decouple the control of reactive power from the active or DC power to be injected into the AC network. The use of large passive components leading to large footprint systems. Self-commutated voltage source converter HVDC transmission systems were developed to address the shortcomings associated with the line commutated current source converter based HVDC transmission systems.
Part1
This part aims to clarify the advantages and disadvantages of different HVDC technologies, i.e., LCC and VSC from the broader context of large power evacuation, HVAC grid support and renewable power generation and integration. The tutorial will cover integration of large renewable energy plants, including operation, control and interactions with AC grids. Also, interactions of current source converter (CSC) and voltage source converter (VSC) based HVDC with AC systems through controls and harmonics will be analyzed. AC and DC faults analysis for different HVDC technologies will be discussed. Finally, DC grids will be reviewed and discussed including the
theoretical concepts, technology, control, faults, DC/DC embedded, and protection with particular emphasis on practical implementation aspects and on reported operational issues. For ease of illustration, the tutorial will be supported with simulations performed in MATLAB/SIMULINK.
Part 2
This part will review the fundamental theoretical frameworks that govern operation and control of present generation of multilevel voltage source converters for DC transmission systems. The tutorial will cover selected topics and emphasize particular aspects in effort order to provide a global view of power electronics systems, and to bridge the gap between the traditional power electronics researchers and their counterparts from the power systems.

Khaled H. Ahmed received his PhD degree from University of Strathclyde, UK in 2008. Currently, He is a Senior Lecturer in power electronics at the University of Strathclyde (PEDEC Group). He has over 15 years of research experience in power electronics, renewable energy integration, smart grids, DC/DC Converters and HVDC. He has won funding of £2.1 million as Primary and Co-Investigator on projects funded by Research councils and industry. He was a part of a 2-lecturer team who designed and delivered a continuing professional development (CPD) course on HVDC for the Scottish and Southern Energy (SSE) HVDC technology engineering team, UK. Dr Ahmed has published over 90 technical papers in refereed journals and conferences, 1 book entitled ‘High voltage direct current transmission: converters, systems and DC grids, Wiley-Blackwell, ISBN: 978-1-118-84666-7, 2015.’, 1 book chapter, and a pending patent (PCT/GB2017/051364). Total citations of 3056 and h-index of 24.

Grain P. Adam received a PhD in Power Electronics from University of Strathclyde, UK in 2007. Since April 2008, Dr Adam is with Institute of Energy and Environment, University of Strathclyde in Glasgow, UK. Besides academic research, Dr Adam has contributed to several research and development projects on novel HVDC converters with major manufacturers of HVDC components, and to major European Union research projects on energy such as the TWENTIES of Seventh Framework Programme (FP7) and PROMOTION of Horizon 2020. His research interests are fault tolerant voltage source converters for HVDC applications; modelling and control of HVDC transmission systems and multi-terminal HVDC networks; voltage source converter based FACTS devices. Dr Adam has authored and co-authored three books in applications of power electronics in power systems and renewable energy, and over 100 journal and conference papers in the area of multilevel converters and HVDC systems, and grid integration of renewable power. Dr Adam is an active member of IEEE and IEEE Power Electronics Society, with wide contribution to the reviewing process for several IEEE and IET Transactions and Journals and conferences.