Analysis of Voltage and Current Unbalance in a Multi-Converter Topology for a DC-Based Offshore Wind Farm

High Voltage Direct Current (HVDC) is increasingly being used for electric power transmission over long distances. In the case of offshore wind farms, HVDC becomes more competitive than HVAC beyond a distance of 80 km. In this paper, a DC-based offshore wind farm is under consideration. In order to step-up the voltage before the transmission line, an isolated DC-DC converter is used. This converter is achieved by associating several elementary isolated DC-DC converters. The key issue with this multi-converter topology is the balancing of currents and voltages between the elementary converters. This paper proposes an analysis of the unbalance by taking into account the disparities on the components used within the elementary converters. After this study, a solution is proposed to achieve a satisfactory balancing of currents and voltages.