Architectures and Control for Multi-terminal DC (MTDC) Distribution Network-A Review

Traditional ac distribution network is ushering a new era of transformation toward dc, providing significant solution to its insufficient current carrying capacity, increasing fault currents, poor power quality, difficulty in flexible integration of large-scale renewable energy sources, etc. To address these issues this paper intends to open up an overview of the dc distribution network trends and present technical superiority analysis for multi-terminal dc (MTDC) distribution network. On this basis, MTDC distribution architectures based on voltage sourced converter (VSC) have been proposed and applied with reliability and controllability under consideration, such as hand-in-hand topology, dual-ring topology, half-ring topology and radial-type topology. Furthermore, performance of MTDC distribution networks is discussed and theoretically validated: high voltage stability, short recovery time, large power capacity, flexible power flow controllability, high power quality, plug-and-play functionality for dispersed renewable sources, etc. Besides, two kinds of control schemes with central control or not are discussed and energy optimization of MTDC network is focused. Last of the paper discusses current DC distribution projects and projects under construction. To sum up, MTDC distribution networks are superior to its ac counterpart, while many technical and practical problems remain unsolved.