A Variable Frequency Modulation Strategy for Current-Fed Dual-Active-Bridge Converter to Expand ZVS Range

This article proposes a variable frequency modulation strategy for current-fed dual-active-bridge converter (CFDAB). The proposed strategy aims to render the ZVS of the CFDAB unconstrained by its low-voltage-side (LVS) duty cycle. By varying the switching frequency of the CFDAB, the current ripples on the LVS inductors can be adjusted flexibly. This allows the CFDAB to operate at critical-conduction-mode (CRM) in the conventional ZVS-loss region. The CRM facilitates the ZVS of CFDAB while ensuring low circulating currents on the LVS inductors. Hence, the proposed strategy is able to expand the ZVS range and voltage regulation range of the CFDAB without increasing conduction losses. The effectiveness of the proposed strategy is validated by a 500 W experimental set-up.