Fractional-order composite sliding mode control for 4-DOF tower crane systems with given-performance

Construction tower cranes exhibit significant nonlinear characteristics and high flexibility due to limited control input, posing major challenges for controller design and stability analysis. To achieve anti-sway control while constraining system variables within a safe range, a new given-performance anti-sway control strategy has been successfully developed by combining composite sliding mode control with fractional calculus. Specifically, advanced Mittag-Leffler stability and fractional-order relevant theories are introduced to prove the convergence of the composite sliding surface and all state variables to zero. Time delay information estimates uncertainties, eliminating the requirement of prior knowledge of the upper bound of uncertainty in traditional sliding mode control. The introduced performance function strictly constraints both the actuated and underactuated variables to ensure the given-performance, namely, the actual transient-state and steady-state control performance of the system can be quantitatively predetermined according to practical application requirements. Finally, the superior performance of the method is verified through experiments.