Robust backstepping control via tracking differentiator for electro-hydraulic load simulator based on velocity synchronization

The Electro-Hydraulic Load Simulator (EHLS) is crucial for testing the performance of aircraft hydraulic actuators. However, challenges such as the actuator’s motion disturbance, unmodeled dynamics, and uncertainty disturbances impact the loading performance. This paper proposes a dual-loop control strategy for the EHLS, combining an open-loop velocity synchronization controller and a robust force backstepping controller, working together in parallel.The open-loop velocity synchronization controller is designed to eliminate the primary disturbances caused by the aircraft’s hydraulic actuator movement. Meanwhile, the robust force backstepping controller addresses the residual disturbances from the synchronized motion, as well as both the matched and mismatched disturbances originating from the EHLS. To enhance synchronization within the EHLS, lag compensation is incorporated for both velocity computation and servo valve spool response. An observer is concurrently implemented to estimate unmeasurable system states and manage both matched and mismatched disturbances. Nonlinear tracking differentiators are then integrated into the backstepping controller design to facilitate the computation of derivatives for the virtual control laws, effectively addressing the ‘explosion of complexity’ issue. Stability of the control system is ensured through Lyapunov’s theory, which accounts for both observation and differentiation errors. Experimental results underscore the effectiveness of the proposed control strategy. • A dual-loop (sync + robust force) counters aircraft actuator motion disturbances. • An improved velocity sync controller cuts actuator disturbance by ∼ 50 % in tests. • An observer monitors unknown states and post-sync residual disturbances in EHLS. • A nonlinear tracking differentiator counters ‘complexity explosion’ in backstepping. • All proposed methods have been validated through experiments.