Comprehensive Design Method for Air-Core Transformer in Dual-Active-Bridge Resonant Converter With Wide Output Range

A coreless isolated converter (CLIC) is proposed, which adopts a dual-active-bridge (DAB) architecture with a self-inductance-resonant CLLC tank. All the inductive components are integrated into one air-core transformer (ACT) by utilizing large leakage inductances. Benefiting from the current source characteristic of the tank and a high degree of freedom of triple-phase-shift modulation, a wide output range is achieved. At the electrical parameter level, a design algorithm that considers the strong correlation between ACT inductances and phase-shift angles is introduced to find the optimal values of the two with the goal of minimizing the total loss of the inverters. At the geometric parameter level, two ACT design algorithms are presented to find all ACT configurations with the desired inductances, respectively, for designing the geometries of coaxial stacked and coaxial nested ACTs. The Pareto fronts of converter efficiency, ACT volumetric power density (VPD), and ACT gravimetric power density (GPD) are obtained, and the one with balanced performance is selected to build a 5.4-kW prototype with an output range of 250-450 V. The experiment shows that the VPD and GPD of the ACT reach 21.69 kW/L and 15.84 kW/kg, respectively. The proposed CLIC achieves a peak efficiency of 97.62% at full load.