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

This article 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-gallium nitride (GaN)-based 700-W, high power density (6.2 W/cm3) experimental proof-of-concept was built for a conversion from a variable input bus voltage (380-420 V) to 12-V output at a resonant frequency of 2 MHz. 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 fundamental harmonic approximation (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.