Authors:
Alberto Bemporad,
Francesco Borrelli,
Manfred Morari,
Volume: 1, Page 1810 Paper number 2601
Abstract:
In this paper we propose a procedure for synthesizing piecewise linear
optimal controllers for hybrid systems and investigate conditions for
closed-loop stability. Hybrid systems are modeled in discrete-time
within the mixed logical dynamical (MLD) framework introduced by Bemporad
and Morari (1999), or, equivalently as piecewise affine (PWA) systems.
A stabilizing controller is obtained by designing a model predictive
controller (MPC), which is based on the minimization of a weighted
1/infinity-norm of the tracking error and the input trajectories over
a finite horizon. The control law is obtained by solving a mixed-integer
linear program (MILP) which depends on the current state. Although
efficient branch and bound algorithms exist to solve MILPs, these are
known to be NP-hard problems, which may prevent their on-line solution
if the sampling-time is too small for the available computation power.
Rather than solving the MILP on line, in this paper we propose a different
approach where all the computation is moved off line, by solving a
multiparametric MILP (mp-MILP). As the resulting control law is piecewise
affine, on-line computation is drastically reduced to a simple linear
function evaluation. An example of piecewise linear optimal control
of the heat exchange system considered in Hedlund and Rantzer (1999)
shows the potential of the method.
Authors:
Kagan Gokbayrak,
Christos G. Cassandras,
Volume: 1, Page 1816 Paper number 2602
Abstract:
We consider optimal control problems for hybrid systems with a separable
cost structure allowing us to decompose them into two components: a
lower-level component with time-driven dynamics (describing the physical
state of the system) interacting with a higher-level component with
event-driven dynamics (describing the changes in the operating modes
of the system). We develop a hybrid controller which aims at jointly
optimizing the performance of both hierarchical components. We demonstrate
this approach on two problems: a linear system switching from one operating
mode to another and a multistage manufacturing system. In the first
problem, the main difficulty is due to the coupling of the physical
states across modes, whereas in the second it is due to the nondifferentiable
event-driven dynamics.
Authors:
Xuping Xu,
Panos J. Antsaklis,
Volume: 1, Page 1822 Paper number 2603
Abstract:
In optimal control problems of switched systems, in general, one needs
to find both optimal continuous inputs and optimal switching sequences,
since the system dynamics vary before and after every switching instant.
In a previous paper, we proved that an optimal control problem can
be posed as a two stage optimization problem under some additional
assumptions. In general, the two stage optimization problem is still
difficult to solve analytically. In this paper, we develop a search
algorithm to explore the solution of the two stage optimization problem
and find useful suboptimal solutions. This algorithm is motivated by
the idea of dynamic programming which studies the value functions.
The algorithm is used to determine suboptimal solutions for general
switched linear quadratic problems
Authors:
Bo Lincoln,
Bo Bernhardsson,
Volume: 1, Page 1828 Paper number 2604
Abstract:
This paper considers off-line optimization of a switching sequence
for a given finite set of linear control systems and joint optimization
of control laws. A linear quadratic full information criterion is optimized
and dynamic programming is used to find the optimal switching sequence
and control laws. The main result is a method for efficient pruning
of the search tree to avoid combinatoric explosion. A method to prove
optimality of a found candidate switch sequence and corresponding control
laws is presented.
Authors:
Omid Shakernia,
George J. Pappas,
Shankar Sastry,
Volume: 1, Page 1834 Paper number 2605
Abstract:
A problem of great interest in the control of hybrid systems is the
design of least restrictive controllers for reachability specifications.
Controller design typically uses game theoretic methods to compute
the region of the state space for which there exists a control such
that for all disturbances, an unsafe set is not reached. In general,
the computation of the controllers requires the steady state solution
of a Hamilton-Jacobi partial differential equation which is very difficult
to compute, if it exists. In this paper, we show that for special
classes of hybrid systems where the continuous vector fields are linear,
the controller synthesis problem is semi-decidable: There exists a
computational algorithm which, if it terminates in a finite number
of steps, will exactly compute the least restrictive controller. This
result is achieved by a very interesting interaction of results from
mathematical logic and optimal control.
Authors:
Michael S. Branicky,
Tor Arne Johansen,
Idar Petersen,
Emilio Frazzoli,
Volume: 1, Page 1840 Paper number 2606
Abstract:
Many control problems of interest can be cast as an optimal hybrid
system control problems, wherein an objective function represents some
global goals and the input at each time instant is a choice among a
finite set of control laws. There are many approaches to solving such
problems in the literature, all based on dynamic programming in some
form or another, and all suffering from overwhelming computational
complexity. Herein, we attempt to lower this complexity by examining
techniques that take advantage of the underlying properties of the
individual controllers among which we are switching. We call this
process ``behavioral programming,'' since we are now attempting to
perform dynamic programming at the more abstract level of behaviors
of the constituent systems. We present our paradigm and discuss two
arenas of its use: motion planning for autonomous agents and LQR with
state and input constraints. Applications to helicopter and wheel
slip control are used to illustrate problem-solving in each of these
arenas, respectively.
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