Discrete pulse frequency modulation control with sliding-mode implementation on LLC resonant DC/DC converter via input-output linearisation

In this study, a novel discrete pulse frequency modulation with sliding-mode control (SMC) implementation of LLC resonant converter is proposed. SMC is employed to cope with the variable dynamic characteristics of LLC resonant converter. The control-oriented dynamic model is first developed by extended describing function method. In order to achieve an optimised output voltage dynamic response, the sliding surface is derived based on the input-output linearisation concept. The proposed sliding-mode controller provides inherent strong robustness against the dynamic drift issues. Meanwhile, the digital SMC signal is insensitive to the non-linear parasitic capacitor of optocoupler. Furthermore, the dynamic performances are significantly improved for the applications of strict dynamic requirements. The theoretical analysis and the attractive dynamic performance are verified by simulation and experimental results.