A novel control approach based on second order sliding modes & its application to hydraulic drives

Sliding modes impose strong robustness toward parametric plant uncertainties and disturbances and accurate tracking performance in control systems. However, in physical systems the application of sliding modes may give rise to undesirable chattering of the control signal due to actuator dynamics. This may be avoided by application of smoothing functions imposing boundary layers on the control constraint, or by carrying out the design in relation to the control derivative. However, such boundary layers introduces additional design parameters and actuator dynamics may not allow the desired control accuracy to be reached. In this paper a novel control approach based on second order sliding modes utilizing the idea of the power rate reaching law is introduced. Dependent on parameters the proposed controller may preserve the main features of sliding controls, while at the same time avoiding control chattering. Simulation studies confirm the announced properties when applied to a hydraulic drive model subjected to strong variations in supply pressure and friction.