Nonlinear extended state observer-based adaptive higher-order sliding mode control for parallel antenna platform with input saturation

This study introduces a robust trajectory tracking controller for a Stewart-type offshore antenna platform considering unmodeled uncertainties and external disturbances under input saturation. First, a finite-time convergent global fast sliding mode surface combining a nonsingular terminal sliding surface and an integral sliding surface is developed and assigned with an anti-windup factor. In addition, a nonlinear extended state observer is used to estimate and compensate for unknown disturbances and unmodeled uncertainties to improve system robustness. An adaptive higher-order sliding mode controller based on a super-twisting algorithm is designed to improve the robustness of the antenna platform control system while reducing slidingmode chattering by dynamically adjusting the control gain value. Finally, the Lyapunov theory is used to guarantee system stability in the presence of lumped uncertainties and input nonlinearity. The effectiveness of the proposed approach is verified by simulations. The integral of the absolute error of the proposed approach is 78.0% lower than that of sliding mode controller based on PID sliding mode surface.