Effective Design Methodology of CLLC Resonant Converter Based on the Minimal Area Product of High-Frequency Transformer

Abstract

In DC microgrids, CLLC topology is commonly applied for battery integration. It provides galvanic separation, the ability to integrate a high-frequency transformer into the resonance circuit, and the ability to operate in a wide range of voltage. Moreover, it assures zero voltage switching conditions for all switches and zero current switching conditions for secondary side switches, which enables obtaining high efficiency. This paper presents a clear and effective approach to design a methodology for a CLLC DC/DC converter, especially a resonant tank. High-frequency transformer is fully integrated in a resonant tank. Its size is minimal and based on area product parameter Ap. An equivalent scheme for first harmonic approximation analysis is presented with inclusion of parasitic elements. Based on it, the analytical formulas are provided, which enable graphical determination of working characteristics. It was proved that the model increases the accuracy of the results. The conditions of ZVS and maximal magnetizing inductance are established, including parasitic capacitances of secondary side switches and transformer parasitic capacitances. Based on the proposed design methodology, as the proof of concept, a small-power prototype with a GaN transistor was built operating at 364 kHz. Converter losses were determined through analytical expressions and compared with the experimental and simulation results.