Nonlinear Control: The Green Years
Alberto Isidori, University of Rome, Italy
Abstract:
Nonlinear Control emerged, as a field, in the early 1970s and reached a stage of full maturity by the end of the 1980s, more or less by the time of the First IFAC Symposium on Nonlinear Control Systems Design. This lecture is a tribute to authors whose ideas, intuitions and results have shaped this field in its adolescence: the Green Years 1970-1990. The decade 1960-70 saw enormous progresses in linear system theory: begun with the introduction of the concepts of controllability and observability, the theory quickly evolved toward the development of sophisticated (mostly geometric) methods of analysis and design. In a nutshell, these methods provided a full answer to the basic conceptual question: “what can be achieved by means of feedback ?” The Green Years of nonlinear control saw a collective effort trying to establish an equivalent corpus of theories and results for nonlinear systems. This fascinating intellectual adventure initiated with the pioneering results of Hermann and Lobry on nonlinear controllability and continued with the landmark contributions of Sussmann and Jurdjevic, Brockett and Krener. Differential geometry emerged as the “tool of choice” for the analysis of the internal structure of a system from the control viewpoint. By the mid 1970s, a fundamental contribution by Hermann and Krener demonstrated how the concept of decomposition of a system into controllable / uncontrollable (observable / unobservable) parts and the concept of system minimality could be phrased in terms bearing a surprising analogy with corresponding known concepts in linear system theory. The stage was set for the big leap ahead: the development of systematic methods to address the question: “how can feedback influence the structure of a nonlinear system ?” Driving forces in the 1980s were the research efforts addressed to the understanding the nonlinear analogue of the concept of transmission zero and to the exploitation of this concept in problems of stabilization and tracking. This marked a beginning of a successful research trend which, by the end of the decade, was heavily and positively influenced by the newly-introduced concept of input-to-state stability, with a fresh approach to the study of stability of interconnected system.
Biography:
Alberto Isidori, born in Rapallo (Italy) in 1942, obtained his Laurea degree in Electrical Engineering from the University of Rome in 1965 and the Libera Docenza in Automatic Control from the University of Rome in 1969. Since 1975, he is Professor of Automatic Control at this University. He has held visiting positions in various leading Universities, which include the University of Illinois at Urbana-Champaign, the University of California at Berkeley, the ETH in Zurich. Since 1989 he has also been regularly collaborating with Washington University in St. Louis. In 1996, at the opening of 13th IFAC World Congress in San Francisco, Dr. Isidori received the “Georgio Quazza Medal”. This medal is the highest technical award given by the International Federation of Automatic Control, and is presented once every third year for lifetime contributions to automatic control science and engineering. The Georgio Quazza Medal was awarded to Dr. Isidori for “pioneering and fundamental contributions to the theory of nonlinear feedback control”. He is also the recipient of the Ktesibios Award, from the Mediterranean Control Association (in 2000) and of the Bode Lecture Award, from the Control Systems society of IEEE (in 2001). In 1986 he was elected Fellow of IEEE and in 2005 he was elected Fellow of IFAC. He has been President of the European Union Control Association in the biennium 1995-1997, and is currently President of IFAC. He was the organizer or co-organizer of several international Conferences on the subject feedback design for nonlinear systems. In particular, he was the initiator a permanent series of IFAC Symposia on this topic.
