Fractional-order super-twisting sliding mode active disturbance rejection control for electro-hydraulic position servo systems

Abstract To address the inherent nonlinearity, time-varying dynamics, and disturbance susceptibility of electro-hydraulic position servo systems in high-precision applications like aerospace actuators, this article proposes a fractional-order super-twisting sliding mode active disturbance rejection control (FOSSMC). Incorporating fractional calculus into the integral sliding surface enables the construction of smoother fractional-order sliding mode switching terms. The inherent long-memory property of these operators effectively suppresses low-frequency disturbances, thereby resolving the trade-off dilemma between persistent chattering and rapid convergence inherent to conventional sliding mode control. Crucially, the novel synthesis of fractional-order operators with super-twisting sliding mode control reaching law and active disturbance rejection control framework provides extra tuning freedom (through orders λ 1 , λ 2 ) to simultaneously accelerate convergence and eliminate high-frequency switching artifacts. Simulations demonstrate 37.25% faster rise time (0.32 s), 0.008 mm steady-state error (meeting ISO 4400 Class H precision), 18.37% lower sinusoidal tracking error, and Monte Carlo-validated robustness to ±15% parameter variations – satisfying industrial demands for aerospace actuators and hydraulic stamping machinery.