Sliding mode control for nonlinear systems

In the conventional sliding mode control, a discontinuous control signal is applied to achieve the sliding condition. This control makes the system invariant to parametric uncertainty and external disturbance, but also causes chattering. Modified approaches are introduced to eliminate chattering at the cost of the invariance property or accuracy. This paper describes the use of the concept of extended systems, such that a continuous control is obtained, using the sliding mode control design scheme. A sliding surface is assigned such that the sliding mode motion will occur as the proposed control law is applied. This results in a system with global invariance.