HV multi-terminal DC lines as the backbone of the energy transmission system – A research plan to tackle challengesChristos Christodoulou, Stavros Lazarou, Elias Zafiropoulos, Vasiliki Vita and Lambros EkonomouMATEC Web Conf., 292 (2019) 01067DOI: https://doi.org/10.1051/matecconf/201929201067