Sliding Mode Control of a 2-MHz All-GaN based 700W 95.6% Efficient LLC Converter

This paper analyzes and develops a generalized harmonic approximation (GHA) based small-signal modeling approach, thus incorporating the effect of all the higher order harmonic components present in the system. Adhering to the plant response extracted from the small-signal model, a comprehensive sliding mode control (SMC) based closed loop controller is employed, with thoroughly laid constraints pertaining to the dynamic response of the system, thus ensuring faster transient response and better stability under various operating conditions. An all-GaN based 700W, high power density (6.2 W/cm³) experimental proof-of-concept was built for a conversion from a variable input bus voltage (380-420V) to 12V output at a resonant frequency of 2MHz. The results portrayed a steady state peak efficiency of 95.65%, with an improvement of 2.2% over the state-of-the-art (SOA) operable at MHz frequency. Further, comparison of the dynamic response of the proposed control scheme with the conventional FHA-derived SMC controller for two load changes (10% -90% load step up and 90% -10% load step down) portrayed a 62.9% reduction in settling time and a 44.1% reduction in over/undershoot.