Adaptive time-varying sliding mode control for hydraulic servo system

This paper studies the position control of an electro-hydraulic servo system. Because the dynamics of the system are highly nonlinear and have large extent of model uncertainties including big changes in load and hydraulic parameters, which are unmatched, a time-varying sliding mode control approach combined with adaptive control is proposed based on Lyapunov analysis. The time-varying sliding mode control avoids the reaching phase of conventional sliding mode control, thus the control method proposed can be robust all the time. Adaptive control is used to identify the system parameters to overcome the influence of the uncertain parameters and disturbances. Simulation results indicate that the control approach has nice global robustness and improves position tracking accuracy considerably.