Robust redesign of adaptive control

1982 21st IEEE Conference on Decision and Control, 1982

IEEE Transactions on Automatic Control, 2000

IEEE Transactions on Automatic Control, 1992

IEEE Transactions on Automatic Control, 1986

2003

International Journal of Adaptive Control and Signal Processing, 2006

Automatica, 1991

Adaptive Control covers a set of techniques which provide a systematic approach for automatic adjustment of controllers in real time, in order to achieve or to maintain a desired level of control system performance when the parameters of the plant dynamic model are unknown and/or change in time. Consider first the case when the parameters of the dynamic model of the plant to be controlled are unknown but constant (at least in a certain region of operation). In such cases, although the structure of the controller will not depend in general upon the particular values of the plant model parameters, the correct tuning of the controller parameters cannot be done without knowledge of their values. Adaptive control techniques can provide an automatic tuning procedure in closed loop for the controller parameters. In such cases, the effect of the adaptation vanishes as time increases. Changes in the operation conditions may require a restart of the adaptation procedure. Now consider the case when the parameters of the dynamic model of the plant change unpredictably in time. These situations occur either because the environmental conditions change (ex: the dynamical characteristics of a robot arm or of a mechanical transmission depend upon the load; in a DC-DC converter the dynamic characteristics depend upon the load) or because we have considered simplified linear models for nonlinear systems (a change in operation condition will lead to a different linearized model). These situations may also occur simply because the parameters of the system are slowly time-varying (in a wiring machine the inertia of the spool is time-varying). In order to achieve and to maintain an acceptable level of control system performance when large and unknown changes in model parameters occur, an adaptive control approach has to be considered. In such cases, the adaptation will operate most of the time and the term non-vanishing adaptation fully characterizes this type of operation (also called continuous adaptation). Further insight into the operation of an adaptive control system can be gained if one considers the design and tuning procedure of the " good " controller illustrated in Fig. 1.1. In order to design and tune a good controller, one needs to:

2004

The emphasis of this thesis is on developing a theoretical framework for the practical design of adaptive systems. The state of the art in industrial adaptive control is to combine a parameter estimator with an (existing) linear control-loop. The success of the approach depends upon the knowledge of the physical parameters after completion of the estimation process. In the presence of disturbances, though, a correct estimation of the parameters is impossible. It is first shown how a system with unknown parameters can be controlled adaptively, without relying on parameter convergence. Following this, three classes of disturbances and the corresponding methods to reject them are developed: external disturbances, unmodelled dynamics and time-variations. In the latter case, a new algorithm based on multiple adaptive models is presented which was developed at Yale University during regular visits of the author at the Center for Systems Science. An experimental study of an adaptively cont...

Proceedings of the IEEE Conference on Decision and Control, 2008