Topology Research of DC/DC Converters for Offshore Wind Farm DC Collection Systems

The DC collection systems of offshore wind farms avoid many problems that the AC collection systems encounter, such as multistage boost, connection of a large number of inductors, and bad stability performance. Besides, the DC collection systems need less equipment investment and are quite simple to design. As one of the key components of DC collection systems, DC/DC converters with high voltage ratio are of great importance. This paper firstly investigated the grid configuration, system control and voltage determination of the medium voltage (MV) collection lines of parallel DC collection systems. Secondly, an analysis of the technological requirement for medium and high voltage DC/DC converters in offshore wind farms was conducted with regard to power, voltage ratio and isolation. Furthermore, on the basis of the existent topology research, the topologies of the multiple phase-shift three level DC/DC converter and the modular multilevel DC/DC (M2DC) converter applicable for wind farms were proposed. Finally, the theoretical feasibility of the proposed topologies was verified by simulations, which shows that the control strategy of the proposed topologies can meet the requirements of the whole DC collection systems.