Light Load Efficiency Improvement of Flying Capacitor-type Current-Fed DAB Converter for 1500V DC-grid

This paper proposes a three-level current-fed dual active bridge (DAB) converter to achieve a wide high-efficiency range for DC voltage and load variation. The proposed control provides zero voltage switching (ZVS) by triangular current mode (TCM) under a wide DC voltage range. Additionally, the transformer root mean square (RMS) current is drastically reduced compared with the conventional control because the DC-voltage ratio is regulated by voltage control to match with the transformer turn ratio. Moreover, the proposed control improves the light load efficiency using the full-bridge (FB) and the half-bridge (HB) modes. The loss analysis results show that the proposed control reduces switching by 46%. The conduction losses were reduced by 53%. The proposed three-level current-fed DAB converter achieves an efficiency of 93.5% or higher over a wide voltage range from 160V to 320V. Finally, the experimental results indicated that the total loss is reduced by 63% at 0.2p.u.