Variable Frequency Phase-Difference Controlled CLLC Resonant Bidirectional DC-DC Converter Featuring Wide-Range ZVS Performance and Reactive Power Reduction

Any types of dual active bridge (DAB) converters based on the non-resonant circuit topology suffer from sever limitation of soft switching under the light load condition. As a solution for this technical issue, a symmetrical resonant tank-assisted bidirectional dc-dc converter (RBDC) is presented in this paper. The proposed RBDC features the variable frequency phase difference control (VF-PDC) for minimization of reactive power with a wide range of soft switching operations. The CLLC series resonant tanks offer symmetrical steady-state characteristics of the load power and voltage regulations in the forward and reverse mode power flows, which is advantageous for configuring a simple controller. The principle of the power regulation is described with the frequency-domain analysis of RBDC, whereby a wide range of soft switching operation and minimization of reactive power are theoretically demonstrated. The experimental verification is carried out with a 500W prototype, where actual efficiency is improved 1.4% and reactive power is reduced 75% by adopting the VF-PDC.