Tracking nonlinear non-minimum phase systems using sliding control

Abstract

Nonlinear systems affine in the input, and having a well-defined (vector) relative degree are considered. The invertibility of the input output dynamics can be used to achieve tracking of smooth desired trajectories if the associated ‘zero-dynamics’ are stable. We consider tracking in nonlinear systems with unacceptable zero-dynamics (i.e. non-minimum phase systems). The desired trajectories are assumed to be generated by some exosystem. We use sliding control to achieve tracking independent 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 modified desired trajectory for the new output to track such that in the process, the original output tracks the original desired trajectory asymptotically.