Position Control of an Electro-Hydraulic Servosystem - A Non-Linear Backstepping Approach

This paper studies the control of an electro-hydraulic servosystem using a non-linear backstepping based approach. These systems are known to be highly non-linear due to many factors as leakage, friction and especially the fluid flow expression through the servo-valve. Another fact, often neglected or avoided, is that such systems have a non-differentiable mathematical model for bi-directional applications. All these facets are pointed out in the proposed model of this paper. Therefore, the control of this class of systems should be based on non-linear strategies. Many experiments showed the failure of classic control with electro-hydraulic systems, unless operating in the neighborhood of a desired value or reference signal. The backstepping is used here to overcome all the non-linear effects. The model discontinuity is solved in this paper, by approximating the non-differentiable function by a sigmoid, so that the backstepping could be used without restrictions. In fact, simulation results show the effectiveness of the proposed approach in terms of guaranteed stability and zero tracking error.