Super Twisting Observer-Based Fast Terminal Sliding Mode Control with Dual-Term Hyperbolic Reaching Law: Experimental Validation on Buck Converter

This paper proposes a super twisting observer-based fast terminal sliding mode control scheme with a novel dual-term reaching law for output voltage regulation of a DC–DC buck converter under disturbances. The proposed reaching law replaces the discontinuous sign function with a continuous hyperbolic tangent function, resolving the fundamental chattering–convergence trade-off inherent in classical reaching laws. The first term employs an exponential gain structure to accelerate convergence when system states are far from the sliding surface, while the second fractional-power term ensures rapid terminal-phase positioning in the vicinity of the surface. A fast terminal sliding surface is incorporated to further reduce settling time, and a super-twisting observer estimates matched disturbances arising from load and input voltage variations using only the output voltage measurement, eliminating the need for additional current sensors. Lyapunov-based stability proofs are provided for both the observer and the controller. Simulation results demonstrate that the proposed reaching law achieves a convergence time of 0.0403 s with the lowest tracking error among all compared methods: RMSE and MAE are reduced by 45.3% and 58.4%, respectively, relative to the exponential reaching law, while the chattering rate value decreases by 13.0%. Real-time experimental validation on a dSPACE1104 platform confirms that the proposed controller achieves fast reference voltage tracking, maintains tight output voltage regulation under load variations, and effectively rejects input voltage disturbances, demonstrating superior convergence speed, chattering attenuation, and disturbance rejection capability.