Engineering application architecture study on an LCC parallel MTDC transmission system

Multi‐terminal DC (MTDC) transmission system is one of the effective technical means to perform a wide range connection of energy and load centres, also it has strong competitiveness and is economic efficiency. This study proposes full‐scale studies on engineering application architecture of an MTDC system. Firstly, advantages and weaknesses of several typical types of MTDC are analysed, and based on the LCC parallel MTDC (P‐MTDC) system, which is most applicable among all types, detailed studies are done on main topology, including polarity‐reversal switches to realise power reversion; secondly, P‐MTDC main circuit calculation method is presented, which decoupled the main circuit calculation into two parts: DC network and converter equation calculation, and general admittance matrix of the DC network is deduced in the study; thirdly, a novel constant‐U control strategy is proposed to simplify the control logic and reduce the control system complexity, by means of setting the nearest point of common coupling from the rectifier station as the voltage control reference point. Finally, one practical case study is taken, for example, of a certain three‐terminal DC project in the world, rated DC parameters are calculated, and a simulation model of MTDC system is built on Electro Magnetic Transient in DC System (EMTDC). The validity of the polarity‐reversal control strategy proposed in the study is demonstrated by simulation.