INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING Int. J. Adapt. Control Signal Process. 2011; 00:1–21 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/acs Adaptive Mixing Control with Multiple Estimators ∗ Simone Baldi 1∗ , Petros A. Ioannou 2 and Elias B. Kosmatopoulos 3 1 Computer Science Department, University of Cyprus (UCY), 1678 Nicosia, Cyprus. 2 Department of Electrical Engineering, University of Southern California, Los Angeles, CA, USA. 3 Dept. of Electrical and Computer Engineering, Democritus University of Thrace, Xanthi, Greece and the Informatics & Telematics Institute, Center for Research and Technology Hellas (ITI-CERTH), Thessaloniki, Greece. SUMMARY A recently proposed adaptive control scheme with mixing involves the use of precalculated candidate controllers whose output is weighted based on the parameter estimates generated by an on-line parameter estimator. It has been shown analytically and demonstrated in simulations that adaptive control with mixing exhibits good performance for the regulation case in the presence of modeling errors, disturbances and time delays. The transient performance however depends on the initial conditions of the parameter estimator and for some initial conditions the transient oscillations may not be acceptable in certain applications. In this paper we combine the controller mixing strategy with a multiple parameter estimation architecture plus a hysteresis switching logic selecting the parameter estimates that generate the smaller estimation errors to decide the mixing of the controllers. We show analytically that this approach, referred to as multi estimator adaptive mixing control (Multi-AMC), achieves stability and stability robustness and we demonstrate using extensive simulations that the scheme achieves consistently better transient performance than the original AMC. In addition we extend the design and analysis to be applicable to the tracking case where the output is required to track a non zero reference signal. The stability and performance of the proposed scheme in the presence of unmodeled dynamics and bounded disturbances has also been analyzed and demonstrated using a numerical example. Copyright c  2011 John Wiley & Sons, Ltd. Received . . . KEY WORDS: Robust Adaptive Control; Multiple-model Mixing Control; Hysteresis switching logic 1. INTRODUCTION A practical control design must be able to maintain performance and stability as well as be robust with respect to plant uncertainties such as unmodeled dynamics and bounded disturbances. In addition it should be able to handle large parametric uncertainties due to unknown values of the physical variables of the plant dynamics. When the model uncertainties are sufficiently small, robust linear time invariant (LTI) control theories, e.g., H ∞ and µ-synthesis, can ensure satisfactory closed-loop objectives. However, failure or degradation of components or unexpected changes typically lead to a large parametric uncertainty, with the result that a single fixed LTI controller may no longer achieve satisfactory closed-loop behavior. Adaptive control was motivated to meet the challenge of handling parametric uncertainties much larger than those that robust control can * This work has been supported by the European Commission FP7-ICT-5-3.5, Engineering of Networked Monitoring and Control Systems, under the contract #257806 AGILE * Correspondence to: S. Baldi. Email: sbaldi@cs.ucy.ac.cy † Please ensure that you use the most up to date class file, available from the ACS Home Page at http://www3.interscience.wiley.com/journal/4508/home Copyright c  2011 John Wiley & Sons, Ltd. Prepared using acsauth.cls [Version: 2010/03/27 v2.00]