TRACKING NONLINEAR NONMINIMUM-PHASE SYSTEMS USING SLIDING CONTROL

Nonlinear systems affine in the input, and having a well-defined (vect or) relative degree are considered. The invertibility of the input out put dynamics can be used to achieve tracking of smooth desired traject ories if the associated 'zero-dynamics' are stable. We consider tracki ng in nonlinear systems with unacceptable zero-dynamics (i.e. non-mini mum phase systems). The desired trajectories are assumed to be generat ed by some exosystem. We use sliding control to achieve tracking indep endent of disturbances entering in the channels of the input. The main idea is (i) to do an output-redefinition such that the zero-dynamics with respect to this new output are acceptable; (ii) to define a modif ied desired trajectory for the new output to track such that in the pr ocess, the original output tracks the original desired trajectory asym ptotically.