Comparison of single-phase and three-phase dual-active bridge DC-DC converters with various semiconductor devices for offshore wind turbines

This paper topics the effect of the phase-number and the semiconductor-device selection on the volume and weight of a medium-voltage (MV) DC-DC converter intended for offshore wind turbines. In recent years, many papers have discussed the transposition from MVAC to MVDC collector grids in offshore wind, where the main motivation is to reduce losses of the system. The authors have identified that the MV DC-DC converter can achieve the efficiency of 98.5% with the three-phase dual-active bridge (DAB) topology and the hybrid pair of 5th- and 6th-generation IGBTs at the switching frequency of 1.5 kHz. Following the efficiency, the volume and weight of the MV DC-DC converter are also important factors in offshore wind turbines. However, from the intuitive point of view, it seems that the single-phase configuration with less number of components and the latest IGBTs with lower losses and better thermal conductivity take less volume and weight than the proposed configuration. In order to clarify the doubt, this paper carries out volume and weight analysis of the MV DC-DC converter with various arrangements of the phase number and semiconductor devices. In the analysis, the worst operation point of the input and output voltages and the required thermal resistance of the cooling system as well as the semiconductor and transformer losses are considered. Moreover, regarding the medium-frequency transformer, the high-frequency loss characteristics of the magnetic cores and windings are taken into account by dimensional analysis. Finally, the analysis elucidates that the MV DC-DC converter with the three-phase DAB topology and the hybrid pair of 5th- and 6th-generation IGBTs can obtain both high efficiency of 98.5% and less volume and weight compared to other configurations.