Robust fixed-time sliding-mode control for a class of nonlinear systems with an electro-hydraulic active suspension case study

This paper presents a robust fixed-time sliding-mode control strategy for an electro-hydraulic active suspension (EHAS) system with nonlinear actuator dynamics and external road disturbances. Due to the hydraulic subsystem, the considered quarter-car model exhibits a relative degree of four with respect to the sprung-mass displacement, which makes fast and robust vibration attenuation particularly challenging. The proposed controller ensures fixed-time convergence of the sliding variable, independently of the initial conditions, while explicitly accounting for model uncertainties and disturbances. The control performance is evaluated through numerical simulations under several representative road profiles, including sinusoidal excitation, speed hump, pothole, and broadband chirp inputs. The simulation study incorporates realistic operating conditions, including actuator saturation, nonlinear hydraulic dynamics and measurement noise. Ride comfort is assessed using ISO 2631–1 criteria, together with road-holding, suspension travel, tracking accuracy, and control smoothness metrics. Comparative results show improved transient performance and ride comfort with respect to classical sliding-mode, backstepping, and PID controllers, while maintaining satisfactory suspension safety and control effort.