Fractional-order sliding mode control for electro-hydraulic position servo systems based on an improved nonlinear extended disturbance observer

The valve-controlled cylinder electro-hydraulic position servo system is a typical nonlinear system, which is affected by load variations, external disturbance forces and other factors during operation, resulting in a significant reduction in control accuracy. To improve the dynamic tracking accuracy of the system, a fractional-order sliding-mode control strategy based on an improved nonlinear extended disturbance observer is proposed. The improved nonlinear extended disturbance observer can effectively estimate the unknown external disturbances and their high-order derivatives in the electro-hydraulic position servo system. Moreover, the estimation accuracy of disturbances is improved and the chattering problem caused by traditional functions is solved by introducing nonlinear compensation terms and a new smooth nonlinear compensation function. On this basis, a fractional-order sliding mode controller is designed, and a fractional-order operator is introduced into the sliding mode surface, which provides more control degrees of freedom and can more effectively improve the system tracking accuracy and transient response. Finally, the designed controller is simulated and verified by MATLAB/Simulink, and the control effects of the system under different working conditions and signals are analyzed. The results show that the designed fractional-order sliding mode controller with the improved nonlinear extended disturbance observer can effectively improve the position-tracking accuracy, transient performance and anti-interference ability of the electro-hydraulic position servo system, and it has better robustness and control effects.