Design and Comparison of Two Nonlinear Tracking Algorithms for Quasilinear Systems with Unmatched Perturbations

This article is concerned with the design of two sliding mode controllers for the robust tracking control of a class of uncertain systems with linear nominal part and perturbations (disturbances, uncertainties and nonlinear loads) which can be both matched and unmatched. The proposed three-term feedback control architecture consists of a linear state feedback term, a feedforward term and a nonlinear term. A 'Reference Model' approach is employed for the design of the three-term tracking controller. For its nonlinear part two separate variants are investigated: the conventional Sliding Mode (cSMC) and the integral Sliding Mode (iSMC). A systematic derivation of the two Sliding Mode controllers is presented along with the design of the nonlinear gains. The numerical examples demonstrate and compare the proposed methodologies on a single input nominally unstable plant.