Authors:
Ali Jadbabaie,
John Hauser,
Volume: 1, Page 4945 Paper number 1781
Abstract:
Receding horizon control is based on iteratively solving an open-loop
finite horizon optimization problem. Despite its success in a variety
of industrial applications, theoretical issues such as stability were
not completely addressed until recently. It was shown in [JYHcdc99]
that by utilizing a suitable Control Lyapunov Function (CLF) as terminal
cost, the stability of the receding horizon scheme can be guaranteed
and the region of attraction of the receding horizon controller can
be estimated. The key point in this approach, which made it different
from others, was removal of additional stability constraints, hence
making the optimizations much easier to solve. A requirement implied
in the previous results was being able to solve the optimizations
globally . In this paper, that assumption is removed and it is shown
that the optimality can be replaced by an improvement property. Specifically,
instead of requiring the trajectories to be optimal, it is required
that a certain amount of decrease in the cost is obtained at each receding
horizon iteration. It is further shown that there always exist a sequence
of controls which guarantee the necessary decrease in the cost. A
numerical example using the inverted pendulum is presented to illustrate
this point.
Authors:
Eric C. Kerrigan,
Jan M. Maciejowski,
Volume: 1, Page 4951 Paper number 1264
Abstract:
An understanding of invariant set theory is essential in the design
of controllers for constrained systems, since state and control constraints
can be satisfied if and only if the initial state belongs to a positively
invariant set for the closed-loop system. The paper briefly reviews
some concepts in invariant set theory and shows that the various sets
can be computed using a single recursive algorithm. The ideas presented
in the first part of the paper are applied to the fundamental design
goal of guaranteeing feasibility in predictive control. New necessary
and sufficient conditions based on the control horizon, prediction
horizon and terminal constraint set are given in order to guarantee
that the predictive control problem will be feasible for all time,
given any feasible initial state.
Authors:
Alberto Bemporad,
Fabio D. Torrisi,
Manfred Morari,
Volume: 1, Page 4957 Paper number 1678
Abstract:
In their recent paper (Bemporad et al., 2000), the authors provided
a tool for obtaining the explicit solution of constrained model predictive
control (MPC) problems by showing that the control law is a continuous
piecewise affine (PWA) function of the state vector. Therefore, the
feedback interconnection between the MPC controller and a linear system,
or a PWA system (e.g., a PWA approximation of a nonlinear system),
is a PWA system. For discrete-time PWA and hybrid systems, we presented
an algorithm for verification/reachability analysis in (Bemporad, Torrisi,
Morari, 2000). In this paper, we formulate the performance analysis
problem of closed-loop PWA systems (including MPC feedback loops where
the prediction model and the plant model could be different) as a reachability
analysis problem, and use our algorithm to obtain a tool for characterizing
(i) the set of states for which the evolution is feasible, (ii) the
domain of stability, (iii) the performance of the closed-loop.
Authors:
Hayco H.J. Bloemen,
Ton J.J. van den Boom,
Henk B. Verbruggen,
Volume: 1, Page 4963 Paper number 1213
Abstract:
Hammerstein systems are a class of systems represented by a static
nonlinearity at the input followed by a linear dynamic block. In this
paper the static input nonlinearity is transformed into a polytopic
description. The remaining uncertain linear model is used in a MPC
algorithm of which the optimization problem involves minimization of
a linear objective function subject to Linear Matrix Inequalities (LMIs),
which is a convex problem. A procedure is presented to remove a number
of LMIs from the optimization problem, prior to solving it. By means
of an iterative procedure the conservatism of the polytopic description
can be reduced. Nominal closed loop stability of this Hammerstein MPC
algorithm is guaranteed. A comparison is presented between the proposed
algorithm and an algorithm which removes the nonlinearity from the
control problem via an inversion.
Authors:
Fernando A. C. C. Fontes,
Volume: 1, Page 4969 Paper number 1095
Abstract:
We propose a Model Predictive Control (MPC) framework to generate feedback
controls for time-varying nonlinear systems with input constraints.
One of the main features of this framework is to allow the feedback
laws to be discontinuous and thereby enlarge the class of nonlinear
systems that can be stabilized by continuous-time MPC. We consider
a continuous-time MPC framework and perform a continuous-time stability
analysis while considering that the inter-sampling times are nonzero
and that the open-loop optimal control problems are solved at every
sampling instant. The feedback law generated by MPC is not a function
of the state at every instant of time, rather it is a function of
the state at the last sampling instant. The trajectories resulting
from this ``sampling-feedback'' are well-defined even when the feedback
is discontinuous. Important classes of nonlinear systems that could
not be stabilized by a continuous feedback, such as the nonholonomic
systems, can now be addressed in a continuous-time MPC framework.
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