High Ratio DC/DC Converter for Offshore Wind Farms with MVDC Collection System

Large-scale long-distance offshore wind farms with MVDC collection system are rapidly becoming a preferred choice for power transmission. The high ratio DC/DC converter to interconnect the MVDC collection and HVDC transmission systems remains the technical hurdle. It suffers large input current and high output voltage, as a result the semiconductors must be rated with the highest current and voltage stress. This paper proposes a new DC/DC converter topology, which is comprised of mature half-bridge submodule strings, low-cost series-connection diodes valves and thy-ristors valves. Alternatively, the strings are connected in parallel to share large current of MVDC, or in series to sustain high voltage of HVDC, resulting in high device utilization and conversion efficiency. The topology structure, operating princi-ple, and circuit design are discussed. The effectiveness of proposed converter is verified by simulation study of a 100MW 35kV/100kV system and experimental study of a 2.4kW 120V/360V scaled down prototype.