Sliding Mode Control Scheme for a CLLC Resonant Converter

In this paper, a comprehensive sliding mode control (SMC) loop design for a CLLC resonant converter is proposed. The major objectives of the proposed SMC are to improve the converter dynamics and to ensure a tight output voltage regulation with respect to any parameter variations and external disturbances. The sliding mode coefficients are selected to achieve both large and small signal stability for the robustness of the converter under different operating conditions. Furthermore, system dynamic performances considering the error dynamics and overshoots are investigated. As verification to the proof-of-concept, a hardware prototype of a bi-directional CLLC resonant converter for plug-in electric vehicle (EV) applications is developed and tested up to 1kW, and the effectiveness of the proposed control solution is verified by the load transients and start-up tests. At a 100% step-change in load power, the sliding mode control achieves 1 ms settling time, which is approximately 0.9 ms faster than the conventional proportional integral (PI) control strategy.