Adaptive backstepping sliding mode control of hydraulic system with nonlinear unknown parameters

The paper proposes an adaptive backstepping sliding mode control method for a hydraulic system with nonlinear unknown parameters, which enter the system equations in a nonlinear way. Backstepping sliding-mode method of system always assume that the parameters are certain and known. But in practical hydraulic system, the parameters are unknown and change. However, the upper bound of the lumped uncertainty is difficult to obtain in advance of practical applications. Therefore, an adaptive law is derived to adapt the value of the lumped uncertainty in real time, and an adaptive backstepping sliding-mode control law is the result. 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.