Fixed-time integral sliding mode control with anti-saturation for linear motor based on disturbance observer

To improve the control performance of linear motors with external perturbations and input saturation, this paper designs an anti-saturation fixed-time integral sliding mode control strategy based on a fixed-time disturbance observer (FxITSMC-FxDO). First, the parameter uncertainties and external disturbances are viewed as composite disturbances. A fixed-time disturbance observer is designed to estimate and compensate for them in real-time, which effectively suppresses chattering by estimating the lumped disturbances. Second, by combined-time theory and integral sliding-modetrol, a fixed-time integral sliding-mode controller is designed to accelerate the convergence speed. Moreover, a non-linear anti-saturation compensator is designed based on the actuator saturation effect parameter to enable the system to exit the saturation region quickly. The fixed-time convergence property of the closed-loop system is proved based on the Lyapunov stability theorem. The experimental results show that the proposed control method effectively improves the control accuracy, response speed, and robustness of linear motors. The step response time of the direct drive permanent magnet linear motor is improved by 16.0% compared to the integral sliding mode control method and 12.5% compared to the finite-time sliding mode control method. In sine target tracking, steady-state accuracy is enhanced by 31.3% over ITSMC and 24.1% over FITSMC-FDO. Furthermore, as the sinusoidal tracking frequency increased from 0.5 to 4 Hz, the proposed control strategy maintained relatively low increases in ITAE and ISE.