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 to other transmission methods due to 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 paper introduces two modular multilevel DC/DC converters with high gain, high voltage and galvanic isolation, which can be applied to connect 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 paper. The simulation based on PSCAD/EMTDC and hardware in loop (HIL) experiment based on RTDS are 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.