Minimal order controllers for output regulation of locally stable nonlinear systems

Vivek Natarajan, George Weiss

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


This paper is about the nonlinear error feedback regulator problem. The plant is a nonlinear finite-dimensional single-input-single-output system and it is locally exponentially stable around the origin. It is driven by a linear exosystem with simple eigenvalues on the imaginary axis. The reference signal that the plant output must track is obtained from the state of the exosystem, in a nonlinear way. The regulator problem is to design a dynamic feedback controller, with the tracking error as its input and the control input to the plant as its output, such that (i) the closed-loop system of the plant and the controller is locally exponentially stable and (ii) the tracking error tends to zero for all sufficiently small initial conditions of the plant, the controller and the exosystem. Under the assumption that the regulator problem is solvable, i.e., there exists a solution to the so-called nonlinear regulator equations, we propose a nonlinear controller of order equal to that of the exosystem to solve the regulator problem. In contrast, previous results on the regulator problem have typically proposed controllers of a larger order. The motivation for the nonlinear controller designed in this work is the structure of a linear controller that solves the regulator problem for the plant linearized around the origin, when the reference and disturbance signals are linear functions of the exosystem state. The nonlinear controller has the same state and control operators as the linear controller and the linearization of its (possibly nonlinear) observation operator is the observation operator of the linear controller. An example and a counterexample illustrating the theory are presented.

Original languageEnglish
Title of host publication53rd IEEE Conference on Decision and Control,CDC 2014
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages6
ISBN (Electronic)9781479977468
StatePublished - 2014
Event2014 53rd IEEE Annual Conference on Decision and Control, CDC 2014 - Los Angeles, United States
Duration: 15 Dec 201417 Dec 2014

Publication series

NameProceedings of the IEEE Conference on Decision and Control
ISSN (Print)0743-1546
ISSN (Electronic)2576-2370


Conference2014 53rd IEEE Annual Conference on Decision and Control, CDC 2014
Country/TerritoryUnited States
CityLos Angeles


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