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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:
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American Control Conference
This tutorial paper looks back at almost 50 years of adaptive control trying to establish how much more we need to be able to offer the industrial community an adaptive controller which will be used and referred to with the same ease as existing PID controllers. Since the first commercial adaptive controller, significant progress in the design and analysis of these controllers has been achieved. Various forms of adaptive controllers are now readily available targeting a significant range of industries from process to aerospace. A general overview of adaptive control will allow the reader to place on the map several industrial architectures for such controllers, all with the aim of bridging the gap between academic and industrial views of the topic. Such a presentation of design and analysis tools currently opens a more philosophical question "Has the critical mass in adaptive control been reached?".
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