The study of different unidirectional input parallel output series connected DC‐DC converters for wind farm based multi‐connected DC system

Summary There is increasing interest in interconnecting individual wind turbines in offshore wind farms using DC networks rather than AC networks. However, the output voltage from each turbine/generator is normally low (less than 6 kV), so DC‐DC converters are required to step‐up the voltage to an intermediate level to interconnect the turbine outputs. Another DC‐DC converter is required to step‐up this intermediate voltage to a high level for transmission to the shore. The DC‐DC converter applied to step‐up the voltage from an intermediate voltage to a high level not only needs to operate with high voltage at both input and output, but also be capable of transferring hundreds of megawatts power. In these circumstances, Input Series Input Parallel Output Series (ISIPOS) DC‐DC converter structure is a good option for the application. In this paper, three different kinds of Input Parallel Output Series (IPOS) DC‐DC converters are presented and compared, and it is the first time this comparison has been made. Both the simulation and downscaled hardware test results are provided and analysed, while the best option in different situations is suggested.