Multi-objective optimization and comparison of DC/DC converters for offshore wind turbines

A key enabling technology for DC collection systems in offshore wind farms is a suitable wind turbine DC/DC converter. However, there is no consensus regarding the topology, design, or operating frequency of this converter. This paper presents an optimization and comparison of four DC/DC converter topologies, including 1-phase, 3-phase, unidirectional, and bidirectional converters. The converters are compared in terms of their reliability, volume, weight and losses at switching frequencies ranging from 500 Hz to 5 kHz. The medium frequency transformer for each converter is designed using multi-objective optimization, and the overall converter volume calculation takes into account the insulation requirements and physical configuration of the components. The results show that if only unidirectional operation is required, the 1-phase single active bridge is the preferred option due to its high reliability, small size and low losses with an optimal operating frequency of up to 2.5 kHz. For bidirectional systems, the 1-phase and 3-phase dual active bridge topologies have a similar efficiency and optimal operating frequency of 1 kHz. Despite its higher volume, the 3-phase version is the preferred option due to its higher reliability and lower device stresses, provided there is enough available space.