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Assessment and Future Directions of Nonlinear Model Predictive ...

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626 S.V. Raković <strong>and</strong> D.Q. Mayne5 Conclusions <strong>and</strong> ExtensionsThis note has introduced a relatively simple tube controller for the obstacleavoidance problem for uncertain linear discrete time systems. The robust modelpredictive controller ensures robust exponential stability <strong>of</strong> R, aRCIset–the‘origin’ for the controlled uncertain system. The complexity <strong>of</strong> the correspondingrobust optimal control problem is marginally increased compared with thatfor conventional model predictive control. The proposed robust model predictivescheme guarantees robust obstacle avoidance at discrete moments; thus theresultant controller, if applied to a continuous time system, will not necessarilyensure satisfaction <strong>of</strong> constraints between sampling instants. However, thisproblem can be dealt with as will be shown in a future paper. It is possible toconsider the cases when control objective is merely reaching the target set Trather than stabilizing an “equilibrium point” R⊆T; it is also, in principle,possible to treat the “multi-system” – “multi-target” case. These modificationsare relatively straight–forward, but they require a set <strong>of</strong> appropriate changes. Finally,combining the results reported in [11], an extension <strong>of</strong> the proposed robustmodel predictive scheme to the class <strong>of</strong> piecewise affine discrete time systems ispossible.References[1] F. Blanchini. Set invariance in control. Automatica, 35:1747–1767, 1999. surveypaper.[2] H.L. Hagenaars, J. Imura, <strong>and</strong> H. Nijmeijer. Approximate continuous-time optimalcontrol in obstacle avoidance by time/space discretization <strong>of</strong> non-convex constraints.In IEEE Conference on Control Applications, pages 878–883, September2004.[3] I. Kolmanovsky <strong>and</strong> E. G. Gilbert. Theory <strong>and</strong> computation <strong>of</strong> disturbance invariancesets for discrete-time linear systems. Mathematical Problems in Engineering:Theory, Methods <strong>and</strong> Applications, 4:317–367, 1998.[4] A. B. Kurzhanski. Dynamic optimization for nonlinear target control synthesis. InProceedings <strong>of</strong> the 6th IFAC Symposium – NOLCOS2004, pages 2–34, Stuttgart,Germany, September 2004.[5] A. B. Kurzhanski, I. M. Mitchell, <strong>and</strong> P. Varaiya. Control synthesis for stateconstrained systems <strong>and</strong> obstacle problems. In Proc. 6th IFAC Symposium –NOLCOS2004, pages 813–818, Stuttgart, Germany, September 2004.[6] W. Langson, I. Chryssochoos, S. V. Raković, <strong>and</strong> D. Q. Mayne. Robust modelpredictive control using tubes. Automatica, 40:125–133, 2004.[7] D. Q. Mayne <strong>and</strong> W. Langson. Robustifying model predictive control <strong>of</strong> constrainedlinear systems. Electronics Letters, 37:1422–1423, 2001.[8] D.Q.Mayne,J.B.Rawlings,C.V.Rao,<strong>and</strong>P.O.M.Scokaert. Constrainedmodel predictive control: Stability <strong>and</strong> optimality. Automatica, 36:789–814, 2000.Survey paper.[9] D.Q.Mayne,M.Seron,<strong>and</strong>S.V.Raković. Robust model predictive control <strong>of</strong>constrained linear systems with bounded disturbances. Automatica, 41:219–224,2005.

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