On Observer-Based Control of Nonlinear Systems

Research output: ThesisDoctoral Thesis (compilation)


Filtering and reconstruction of signals play a fundamental role in modern signal processing, telecommunications, and control theory and are used in numerous applications.

The feedback principle is an important concept in control theory. Many different control strategies are based on the assumption that all internal states of the control object are available for feedback. In most cases, however, only a few of the states or some functions of the states can be measured. This circumstance raises the need for techniques, which makes it possible not only to estimate states, but also to derive control laws that guarantee stability when using the estimated states instead of the true ones. For linear systems, the separation principle assures stability for the use of converging state estimates in a stabilizing state feedback control law. In general, however, the combination of separately designed state observers and state feedback controllers does not preserve performance, robustness, or even stability of each of the separate designs. In this thesis, the problems of observer design and observer-based control for nonlinear systems are addressed. The deterministic continuous-time systems have been in focus.

Stability analysis related to the Positive Real Lemma with relevance for output feedback control is presented. Separation results for a class of nonholonomic nonlinear systems, where the combination of independently designed observers and state-feedback controllers assures stability in the output tracking problem are shown. In addition, a generalization to the observer-backstepping method where the controller is designed with respect to estimated states, taking into account the effects of the estimation errors, is presented. Velocity observers with application to ship dynamics and mechanical manipulators are also presented.


Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Control Engineering


  • Observers, Output feedback, Separation principle, The Positive Real lemma, Kalman filter, Backstepping, Robotics, Automation, Chained form systems, reglerteknik, robotteknik, Automatiska system, control engineering, Lyapunov stability, Nonlinear systems, State estimation
Original languageEnglish
Awarding Institution
Supervisors/Assistant supervisor
Award date1999 Dec 16
  • Department of Automatic Control, Lund Institute of Technology (LTH)
Publication statusPublished - 1999
Publication categoryResearch

Bibliographic note

Defence details Date: 1999-12-16 Time: 10:15 Place: Room M:B, Mechanical Engineering Building, Lund Institute of Technology External reviewer(s) Name: Siciliano, Bruno Title: [unknown] Affiliation: Dipartimento di Informatica e Sistemistica, Università degli Studi di Napoli Federico II, Italy ---

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