Frequency optimisation for DC/DC converters in DC-connected offshore wind turbines

In all-DC wind farms, DC/DC converters connect the low voltage wind turbine output to the high voltage DC array. One potential benefit of using DC/DC converters is that they require a relatively small transformer due to their higher frequency operation. However, there is no consensus as to what this frequency should be. This paper aims to determine the optimal operating frequency for DC/DC converters in 15 MW wind turbines connected to an 80 kV DC array. A multi-objective optimisation is performed taking into account the DC/DC converter volume, weight and losses. Frequencies ranging from 500 Hz to 5 kHz were tested for unidirectional, bidirectional, single-phase and three-phase converters. The optimal frequencies for unidirectional and bidirectional converters were found to be approximately 2 kHz and 1 kHz, respectively.