Sliding mode control using only output information

Variable structure control with a sliding mode is an established method of controlling uncertain dynamical systems. Traditional variable structure control systems employ a discontinuous control action to force the system states to remain on a surface, usually a hyperplane, within the state-space. This results in a reduced order, surface dependent motion, known as a sliding mode. This motion is insensitive to disturbances implicit in the input channel, the so-called matched uncertainty, and makes the methodology an attractive one for synthesising robust controllers for uncertain systems. The design approach comprises two components: the design of a surface in the state-space so that the reduced order sliding motion satisfies the specifications imposed on the designer; and the synthesis of a control law, discontinuous about the sliding surface, such that the trajectories of the closed loop motion are directed towards the surface