A Hybrid Bidirectional Full-Bridge CLLC Resonant Converter with Dual-Resonant Frequency for Enhancing Efficiency at Light-to-Medium Loads

The symmetric CLLC resonant converter is a key component in electric power conversion systems, used for interfacing with DC voltage buses in applications such as renewable energy sources, battery energy storage in electric vehicles (EVs), and DC microgrids. It is favored for its bidirectional power transfer, high power density, zero-voltage switching for primary power switches, and soft commutation for output rectifiers. However, a significant drawback of the CLLC converter is the high operating frequency at light loads, leading to increased switching losses and reduced efficiency. To overcome this problem, the paper introduces a hybrid CLLC converter that can dynamically switch between full-bridge and half-bridge configurations, as well as adjust the resonant frequency based on load conditions. This hybrid approach allows the converter to operate in a half-bridge configuration and adjust its resonant frequency, reducing the switching frequency during light-to-medium loads and thereby enhancing operating efficiency. A prototype with a 2kW power rating, designed to connect a 400Vdc bus to an 800Vdc bus, was tested. Experimental results confirmed the proposed converter's effectiveness, demonstrating improved efficiency under light-to-medium load conditions.