A medium frequency transformer (MFT) is a critical component of a dual active bridge (DAB) converter. The winding material recommended in literature is copper (Cu) due to its high conductivity. However, Cu's higher mass density compared to aluminium (Al) reduces the gravimetric power density of the system. Although Al has lower conductivity, the region is identified in this paper where winding losses in Al-wound MFT (Al-MFT) are lower compared to Cu-wound MFT (Cu-MFT). This reduction in losses is due to decreased eddy currents generated in the Al-MFT. Furthermore, the choice of winding material affects the leakage inductance, which is also investigated. The impact on winding losses and leakage inductance is demonstrated by designing two MFTs, rated for 20kVA, 50 kHz, 110/800 V: one with an Al winding and the other with a Cu winding. The analytical results are compared with 3D FEM and further validated through experimentation. To measure winding losses, the transient calorimetric method is adapted for foil windings. The analysis shows that Al-MFT design offers 17.02 % and 16.8 % reduction in secondary and primary winding losses and 28.1 % improvement in gravimetric power density.
