Disturbance Observer-Based Fixed-Time Sliding-Mode Control for Electromechanical Actuators

Electromechanical actuators play a pivotal role in aerospace servo systems; however, their high-precision tracking performance is frequently compromised by external disturbances and system nonlinearities. To address these challenges, this paper proposes a disturbance observer-based fixed-time backstepping sliding-mode control strategy. Firstly, the high-order dynamics are decomposed into load and electrical subsystems employing a backstepping control framework. To effectively handle mismatched external disturbances in the load subsystem, a prescribed-time integral sliding-mode observer is designed, which guarantees accurate disturbance estimation within a prescribed time for feedforward compensation. Subsequently, a fixed-time sliding-mode controller incorporating a segmented reaching law is developed. This controller ensures that tracking errors converge to zero within a fixed time, independent of initial system states, while mitigating chattering. Hardware-in-the-loop experimental results demonstrate the superior performance of the proposed strategy. Compared to conventional methods, the proposed controller significantly enhances transient response under step disturbances by reducing the peak deviation by up to 94% and shortening the recovery time by at least 60%. Furthermore, under sustained sinusoidal disturbances and dynamic tracking scenarios, the output fluctuations and tracking errors are attenuated to negligible levels, thereby exhibiting notable improvements over traditional methods.