A different look at output tracking: control of a VTOL aircraft

An important control problem is output tracking. One approach, for slightly nonminimum phase systems is to approximate the system by a minimum phase one. Another approach is to track signals generated by an exosystem. These methods concentrate on properties of the IO system without any attempt to investigate and use structural properties of the IS system. In this paper the authors propose an alternative point of view based on the following simple remark: if one had a state tracker (i.e. a controller able to track any reference state trajectory), the output tracking would reduce to the generation of a good state reference, which is only an open-loop problem, and hence (hopefully) simpler. The idea is simply to split the output tracking problem into two steps