Analysis and Comparison of Isolated High-Gain High-Voltage DC/DC Converters for Offshore Wind Farm Collection and Integration

With the vigorous development of offshore wind energy, two-stage voltage step-up HVdc transmission has become a better choice compared with other transmission methods due to the lower cost and higher efficiency. It is essential to step-up the medium voltage (MV) level at the collection grid to the high voltage (HV) level at the export line. Therefore, the research on HV dc/dc converters has received widespread attention. This article introduces two modular multilevel dc/dc converters with high gain, HV, and galvanic isolation, which can be applied to connect the MVdc grid and HVdc grid in offshore wind energy systems. The topologies, operation principles, and control strategies of the two converters are illustrated in the article. The simulation based on power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC) and hardware in loop experiment based on real-time digital simulation (RTDS) is completed. The operation principle and control strategy are validated by the simulation results and experiment results. The comparison results in terms of current stresses, costs, and power losses between these two converters and the two representative topologies previously proposed are presented. Then, the overall performance of each topology is evaluated based on the comparison results.