Output Voltage Control of a Half-Bridge LLC Resonant Converter Based on Nonsingular Fast Terminal Sliding Mode Active Disturbance Rejection Control

This paper proposes an output-voltage control method for a half-bridge LLC resonant converter that combines nonsingular fast terminal sliding mode control (NFTSMC) with a linear extended state observer (LESO) to improve dynamic regulation under input-voltage disturbances and load transients. Based on a second-order equivalent model with a lumped disturbance, the LESO provides state and disturbance estimates, while an NFTSMC law replaces the linear state error feedback law in conventional linear active disturbance rejection control (LADRC) to generate the frequency control input with disturbance compensation. Under the assumed disturbance and operating conditions, including boundedness of the lumped disturbance and its derivative and the absence of sustained control-input saturation, theoretical analysis shows bounded observation errors and ultimate convergence of the sliding variable and output-voltage tracking error to small neighborhoods of zero. Simulations of a 240 W system and semi-physical experiments using a dSPACE MicroLabBox and a physical prototype are conducted to compare the proposed method with proportional-integral control and LADRC. In the semi-physical experiments, compared with LADRC, the recovery time and output-voltage fluctuation percentage are reduced by 63.9% and 8.3%, respectively, when the input voltage decreases from 400 to 380 V. When the load current increases from 5.71 to 11.42 A, the corresponding reductions are 29.4% and 20.2%. The results indicate improved dynamic output-voltage regulation and disturbance suppression under the tested operating conditions.