Behaviour of Multi-Terminal Grid Topologies in Renewable Energy Systems Under Multiple Loads

Decarbonization policies adopted worldwide are leading to a steadily increasing deployment of renewable energy sources (RES). In Europe, for example, a multitude of wind farms is built at (predominantly) onshore and (increasingly) offshore sites. The connection of offshore wind farms is expected to promote the realization of Multi Terminal Grids (MTG), which include High Voltage DC (HVDC) transmission systems requiring high voltage inverters. Due to the semiconductor components used in the inverter systems, voltage and current fluctuations occur before and after the inverters, producing harmonics, voltage oscillations and power loss in the transmission system. In this study, transient responses of four representative MTG topologies for renewable energy systems are identified and analyzed by means of MATLAB or NEPLAN models. The study escalates the complexity of the simulation starting from a point-to-point HVDC connection up to the interconnection of five (5) inverter terminals. In order to address all the possible connection options the authors examine different topologies for grid having more than three points. The different responses of the network configurations under study are analyzed and compared. Simulation results are then validated with hardware-in-the-loop experiments in the Smart Grid Simulation Centre of the European Commission's Institute for Energy and Transport (IET).