Asymptotic stability of model reference systems with variable structure control

The application of theory of variable structure systems (VSS) in the design of controllers for single input-single output model reference systems is considered. It is shown that the resulting controller has similar structure as those obtained using the second method of Lyapunov except that the states of the model are also used. The error trajectories move towards the switching surface for all values of the error and continues on it as sliding motions. The present approach clarifies the relationship between stability and nonminimum phase zeros of the plant.