Generalized State-Plane Analysis of Bidirectional CLLC Resonant Converter

The CLLC resonant converter is a promising candidate for high efficient, bidirectional power transfer applications, such as vehicle-to-grid on-board charger and hybrid vehicle dc–dc converter. Nevertheless, the analysis of CLLC still remains challenging because of its complex multiresonant nature and several storage elements. In this article, a circuit analysis method based on change of variables is presented that maps the state-space equations into two decoupled sets of equations. The analyses are carried out in two state-plane coordinate systems, then the results are mapped onto the original region. The proposed method is then used to thoroughly analyze the CLLC resonant converter operating in the continuous conduction mode (CCM). The voltage and current stresses of components, zero voltage switching condition, output voltage gain, output characteristic diagram, and mode boundary of CCM/ discontinuous conduction mode are then obtained. The accuracy of the proposed approach is verified by the experiments on a 3 kW bidirectional CLLC resonant converter with GaN transistors as the primary and secondary side switches. The results confirm the accuracy of the proposed state-plane analysis of the CLLC resonant converter operating in either direction of power transferring.