Indirect adaptive control of an electro-hydraulic servo system based on nonlinear backstepping

This paper studies the position control of an electro-hydraulic servo system using indirect adaptive Backstepping. In fact, electro-hydraulic systems are known to be highly nonlinear and non-differentiable due to many factors as leakage, friction and especially the fluid flow expression through the servo-valve. Backstepping is used here for being a powerful, robust nonlinear strategy and for its ability to ensure a global asymptotic stability of the controlled system without canceling useful nonlinearities. On the other hand, hydraulic parameters such as fluid viscosity and bulk modulus are subjected to variations due to temperature rise. This results in a variation of the viscous friction coefficient. Knowing that the structure of a Backstepping controller relies on the system parameters, it is crucial to use adaptive Backstepping in order to update the controller structure with parameters variation. Emphasis is also on the tuning parameters effect and their influence on the errors dynamic behavior, in addition to the chattering and saturation in the control signal. Results in this work are based on simulations and are compared to those obtained with non-adaptive Backstepping. We will see the effectiveness of the proposed approach in terms of guaranteed stability and zero tracking error in the presence of varying parameters.