ARTICLE IN PRESS Available online at www.sciencedirect.com Automatica ( ) – www.elsevier.com/locate/automatica Implicit fault-tolerant control: application to induction motors Claudio Bonivento a , Alberto Isidori a; b; c , Lorenzo Marconi a ; * , Andrea Paoli a a Center for Research on Complex Automated Systems (CASY) “Giuseppe Evangelisti”, DEIS, Department of Electronic, Computer Science and Systems, University of Bologna, Via Risorgimento 2, 40136 Bologna, Italy b Dipartimento di Informatica e Sistemistica, University of Rome, Italy c Department of Systems Science and Mathematics, Washington University, St.Louis, MO 63130, USA Received 22 January 2003; received in revised form 12 September 2003; accepted 7 October 2003 Abstract In this paper we propose an innovative way of dealing with the design of fault-tolerant control systems. We show how the nonlinear output regulation theory can be successfully adopted in order to design a regulator able to oset the eect of all possible faults which can occur and, in doing so, also to detect and isolate the occurred fault. The regulator is designed by embedding the (possible nonlinear) internal model of the fault. This idea is applied to the design of a fault-tolerant controller for induction motors in presence of both rotor and stator mechanical faults. ? 2003 Elsevier Ltd. All rights reserved. Keywords: Fault-tolerant control; Induction motor; Output-feedback control; Internal model control; Adaptive control 1. Introduction Many eorts in the control community have been re- cently devoted to study “fault-tolerant” control (FTC) sys- tems, namely: control systems able to detect incipient faults in sensors and/or actuators on the one hand and on the other, to promptly adapt the control law in such a way as to pre- serve pre-specied performances in terms of quality of the production, safety, etc. The most common approach in dealing with such a prob- lem (see Frank, 1990 and the reference therein) is to split the overall design in two distinct phases. The rst phase ad- dresses the so-called “fault detection and isolation” (FDI) A preliminary version of this paper has been presented at the IFAC’02 World Congress, Barcelona, July 2002. This paper was recommended for publication in revised form by Associate Editor Jessy W. Grizzle under the direction of Editor Hassan Khalil. This research has been supported by EC-Project IFATIS (intelligent fault tolerant control in integrated systems) funded by the European Commission in the IST programme 2001 of the fth EC framework programme (IST-2001-32122), by ONR under Grant N00014-03-1-0314 and by MIUR. * Corresponding author. Tel.: +39-051-209-3788; fax: +39-051-209-3073. E-mail address: lmarconi@deis.unibo.it (L. Marconi). problem, which consists of designing a dynamical system (lter) which, by processing input/output data, is able to de- tect the presence of an incipient fault and to isolate it from other faults and/or disturbances. Once the FDI lter has been designed, the second phase usually consists of designing a supervisory unit which, on the basis of the information pro- vided by the FDI lter, recongures the control so as to compensate for the eect of the fault and to fulll perfor- mances constraint. In general, the latter phase is carried out by means of a parameterized controller which is suitably updated by the supervisory unit. It is clear from this description that the classical approach to FDI and FTC relies upon a “certainty equivalence” idea extensively used in the context of adaptive control, since it is based on the explicit estimation of unknown time varying signals/parameters (in the specic case the faults) by the FDI lter and the subsequent explicit reconguration of the controller in presence of faults. The aim of this paper is to follow a dierent approach to FTC. Specically, we address the case in which the faults af- fecting the controlled system can be modeled as functions (of time) within a nitely parametrized family. Then, we design a controller which embeds an internal model of this family, whose purpose is to generate a supplementary control action which compensate for the presence of any of such faults, 0005-1098/$ - see front matter ? 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.automatica.2003.10.003