Robustification of the modular tracking controller for the N-Trailers by employing a disturbance observation-compensation loop

This paper is devoted to the control-robustification problem for the modular tracking controller devised for the N-Trailers and recently presented in [15]. Robustification is addressed in the context of parametric uncertainty of the N-Trailer kinematics resulting from the lack of perfect knowledge on the lengths of the trailers and hitching offsets. It is shown that the presence of parametric uncertainty can be brought to the existence of a resultant input-matched disturbance acting in the outer loop of the original modular tracking controller. Through redesigning of the nominal tracking controller by employing an additional disturbance observation-compensation loop, a new composite robust control law is proposed for the uncertain N-Trailer kinematics. It is shown that under some conditions the new control law guarantees uniform ultimate boundedness of an output tracking error for an arbitrarily small ultimate bound, even for substantial model uncertainties. A simulation example illustrates control performance improvement achievable with the new robust controller for the non-standard three-trailer kinematics.