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Assessment and Future Directions of Nonlinear Model Predictive ...

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<strong>Model</strong> <strong>Predictive</strong> Control for <strong>Nonlinear</strong>Sampled-Data SystemsL. Grüne 1 ,D.Nešić 2 , <strong>and</strong> J. Pannek 31 Mathematical Institute, University <strong>of</strong> Bayreuthlars.gruene@uni-bayreuth.de2 EEE Department, University <strong>of</strong> Melbourne, Australiad.nesic@ee.mu.oz.au3 Mathematical Institute, University <strong>of</strong> Bayreuthjuergen.pannek@uni-bayreuth.deSummary. The topic <strong>of</strong> this paper is a new model predictive control (MPC) approachfor the sampled–data implementation <strong>of</strong> continuous–time stabilizing feedback laws. Thegiven continuous–time feedback controller is used to generate a reference trajectorywhich we track numerically using a sampled-data controller via an MPC strategy. Hereour goal is to minimize the mismatch between the reference solution <strong>and</strong> the trajectoryunder control. We summarize the necessary theoretical results, discuss several aspects<strong>of</strong> the numerical implemenation <strong>and</strong> illustrate the algorithm by an example.1 IntroductionInstead <strong>of</strong> designing a static state feedback with sampling <strong>and</strong> zero order hold bydesigning a continuous–time controller which is stabilizing an equilibrium <strong>and</strong>discretizing this controller ignoring sampling errors which leads to drawbacks instability, see [5, 8], our approach is to use a continuous–time feedback <strong>and</strong> toanticipate <strong>and</strong> minimize the sampling errors by model predictive control (MPC)with the goal <strong>of</strong> allowing for large sampling periods without loosing performance<strong>and</strong> stability <strong>of</strong> the sampled–data closed loop. Therefore we consider two systems,the first to be controlled by the given continuous–time feedback which willgive us a reference trajectory, <strong>and</strong> a second one which we are going to controlusing piecewise constant functions to construct an optimal control problem byintroducing a cost functional to measure <strong>and</strong> minimize the mismatch betweenboth solutions within a time interval.In order to calculate a feedback instead <strong>of</strong> a time dependent control function<strong>and</strong> to avoid the difficulties <strong>of</strong> solving a Hamilton-Jacobi-Bellman equation foran infinite horizon problem we reduce the infinite time interval to a finite one byintroducing a positive semidefinite function as cost–to–go. To re–gain the infinitecontrol sequence we make use <strong>of</strong> a receding horizon technique. For this approachwe will show stability <strong>and</strong> (sub-)optimality <strong>of</strong> the solution under certain st<strong>and</strong>ardassumptions.We will also show how to implement an algorithm to solve this process <strong>of</strong> iterativelygenerating <strong>and</strong> solving optimal control problems. The latter one is doneR. Findeisen et al. (Eds.): <strong>Assessment</strong> <strong>and</strong> <strong>Future</strong> <strong>Directions</strong>, LNCIS 358, pp. 105–113, 2007.springerlink.com c○ Springer-Verlag Berlin Heidelberg 2007

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