1,312 research outputs found
Stabilising Model Predictive Control for Discrete-time Fractional-order Systems
In this paper we propose a model predictive control scheme for constrained
fractional-order discrete-time systems. We prove that all constraints are
satisfied at all time instants and we prescribe conditions for the origin to be
an asymptotically stable equilibrium point of the controlled system. We employ
a finite-dimensional approximation of the original infinite-dimensional
dynamics for which the approximation error can become arbitrarily small. We use
the approximate dynamics to design a tube-based model predictive controller
which steers the system state to a neighbourhood of the origin of controlled
size. We finally derive stability conditions for the MPC-controlled system
which are computationally tractable and account for the infinite dimensional
nature of the fractional-order system and the state and input constraints. The
proposed control methodology guarantees asymptotic stability of the
discrete-time fractional order system, satisfaction of the prescribed
constraints and recursive feasibility
Robust model predictive control for discrete-time fractional-order systems
In this paper we propose a tube-based robust model predictive control scheme for fractional-order discrete-time systems of the Grunwald-Letnikov type with state and input constraints. We first approximate the infinite-dimensional
fractional-order system by a finite-dimensional linear system
and we show that the actual dynamics can be approximated
arbitrarily tight. We use the approximate dynamics to design
a tube-based model predictive controller which endows to the
controlled closed-loop system robust stability properties
Discrete-time optimal preview control
There are many situations in which one can preview future reference signals, or future disturbances. Optimal Preview Control is concerned with designing controllers which use this preview to improve closed-loop performance. In this thesis a general preview control problem is presented which includes previewable disturbances, dynamic weighting functions, output feedback and nonpreviewable disturbances. It is then shown how a variety of problems may be cast as special cases of this general problem; of particular interest is the robust preview tracking problem and the problem of disturbance rejection with uncertainty in the previewed signal. . (', The general preview problem is solved in both the Fh and Beo settings. The H2 solution is a relatively straightforward extension ofpreviously known results, however, our contribution is to provide a single framework that may be used as a reference work when tackling a variety of preview problems. We also provide some new analysis concerning the maximum possible reduction in closed-loop H2 norm which accrues from the addition of preview action. / Name of candidate: Title of thesis: I DESCRIPTION OF THESIS Andrew Hazell Discrete-Time Optimal Preview Control The solution to the Hoo problem involves a completely new approach to Hoo preview control, in which the structure of the associated Riccati equation is exploited in order to find an efficient algorithm for computing the optimal controller. The problem tackled here is also more generic than those previously appearing in the literature. The above theory finds obvious applications in the design of controllers for autonomous vehicles, however, a particular class of nonlinearities found in typical vehicle models presents additional problems. The final chapters are concerned with a generic framework for implementing vehicle preview controllers, and also a'case study on preview control of a bicycle.Imperial Users onl
Testing the SOC hypothesis for the magnetosphere
As noted by Chang, the hypothesis of Self-Organised Criticality provides a
theoretical framework in which the low dimensionality seen in magnetospheric
indices can be combined with the scaling seen in their power spectra and the
recently-observed plasma bursty bulk flows. As such, it has considerable
appeal, describing the aspects of the magnetospheric fuelling:storage:release
cycle which are generic to slowly-driven, interaction-dominated, thresholded
systems rather than unique to the magnetosphere. In consequence, several recent
numerical "sandpile" algorithms have been used with a view to comparison with
magnetospheric observables. However, demonstration of SOC in the magnetosphere
will require further work in the definition of a set of observable properties
which are the unique "fingerprint" of SOC. This is because, for example, a
scale-free power spectrum admits several possible explanations other than SOC.
A more subtle problem is important for both simulations and data analysis
when dealing with multiscale and hence broadband phenomena such as SOC. This is
that finite length systems such as the magnetosphere or magnetotail will by
definition give information over a small range of orders of magnitude, and so
scaling will tend to be narrowband. Here we develop a simple framework in which
previous descriptions of magnetospheric dynamics can be described and
contrasted. We then review existing observations which are indicative of SOC,
and ask if they are sufficient to demonstrate it unambiguously, and if not,
what new observations need to be made?Comment: 29 pages, 0 figures. Based on invited talk at Spring American
Geophysical Union Meeting, 1999. Journal of Atmospheric and Solar Terrestrial
Physics, in pres
Direct data-driven control of linear time-varying systems
An identification-free control design strategy for discrete-time linear
time-varying systems with unknown dynamics is introduced. The closed-loop
system (under state feedback) is parametrised with data-dependent matrices
obtained from an ensemble of input-state trajectories collected offline.
Subsequently, controllers guaranteeing bounded closed-loop trajectories,
optimal performance and robustness to process and measurement noise are
designed via convex feasibility and optimisation problems involving purely
data-dependent linear matrix inequalities. For the special case of periodically
time-varying systems, performance guarantees are achieved over an infinite
horizon, based on data collected over a single, finite duration experiment. The
results are demonstrated by means of an illustrative academic example and a
practically motivated example involving a voltage source converter.Comment: This work has been submitted to the IEEE for possible publication.
Copyright may be transferred without notice, after which this version may no
longer be accessibl
Adaptive Robust Control of Biomass Fuel Co-Combustion Process
The share of biomass in energy production is constantly growing. This is caused by environmental and industry standards and EU guidelines. Biomass is used in the process of co-firing in large power plants and industrial installations. In the existing power stations, biomass is milled and burned simultaneously with coal. However, low-emission combustion techniques, including biomass co-combustion, have some negative side effects that can be split into two categories. The direct effects influence the process control stability, whereas the indirect ones on combustion installations via increased corrosion or boiler slagging. The effects can be minimised using additional information about the process. The proper combustion diagnosis as well as an appropriate, robust control system ought to be applied. The chapter is devoted to the analysis of modern, robust control techniques for complex power engineering applications
- …