Adaptive sliding mode control of electro-hydraulic system with nonlinear unknown parameters

In this paper, an adaptive sliding control method is presented for an electro-hydraulic system with nonlinear unknown parameters, which enter the system equations in a nonlinear way. Previous adaptive control methods of hydraulic system always assume that the original control volumes are certain and known, which can guarantee that all system unknown parameters occur linearly. But in practical hydraulic systems, the original control volumes are unknown or change; as a result some unknown parameters appear nonlinearly. The proposed control method in this paper is to present a nonlinear adaptive controller with adaptation laws to compensate for the nonlinear uncertain parameters caused by the varieties of the original control volumes. The main feature of the scheme is that by combining sliding mode control method, a novel-type Lyapunov function is developed to construct an asymptotically stable adaptive controller and adaptation laws, which can compensate for the system uncertain nonlinearities, linear uncertain parameters, and especially for the nonlinear uncertain parameters caused by the various of the original control volumes. The experimental results show that the nonlinear control algorithm, together with the adaptation scheme, gives a good performance for the specified tracking task in the presence of nonlinear unknown parameters.