3,170 research outputs found
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Structure evolving systems and control in integrated design
Existing methods in Systems and Control deal predominantly with Fixed Systems, that have been designed in the past, and for which the control design has to be performed. The new paradigm of Structure Evolving Systems (SES), expresses a new form of system complexity where the components, interconnection topology, measurement-actuation schemes may not be fixed, the control scheme also may vary within the system-lifecycle and different views of the system of varying complexity may be required by the designer. Such systems emerge in many application domains and in the engineering context in problems such as integrated system design, integrated operations, re-engineering, lifecycle design issues, networks, etc. The paper focuses on the Integrated Engineering Design (IED), which is revealed as a typical structure evolution process that is strongly linked to Control Theory and Design type problems. It is shown, that the formation of the system, which is finally used for control design evolves during the earlier design stages and that process synthesis and overall instrumentation are critical stages of this evolutionary process that shapes the final system structure and thus the potential for control design. The paper aims at revealing the control theory context of the evolutionary mechanism in overall system design by defining a number of generic clusters of system structure evolution problems and by establishing links with existing areas of control theory. Different aspects of model evolution during the overall design are identified which include cases such as: (i) Time-dependent evolution of system models from “early” to “late” stages of design. (ii) Design stage-dependent evolution from conceptualisation to process synthesis and to overall instrumentation. (iii) Redesign of given systems and constrained system evolution. Within each cluster a number of well defined new Control Theory problems are introduced, which may be studied within the structural methodologies framework of Linear Systems. The problems posed have a general systems character, but the emphasis here is on Linear Systems; an overview of relevant results is given and links with existing research topics are established. The paper defines the Structural Control Theoretic context of an important family of complex systems emerging in engineering design and defines a new research agenda for structural methods of Control Theory
A classification of techniques for the compensation of time delayed processes. Part 2: Structurally optimised controllers
Following on from Part 1, Part 2 of the paper considers the use of structurally optimised controllers to compensate time delayed processes
Equivalence transformations in linear systems theory
There is growing interest in infinite frequency structure of
linear systems, and transformations preserving this type of
structure. Most work has been centred around Generalised
State Space (GSS) systems. Two constant equivalence
transformations for such systems are Rosenbrock's Restricted
System Equivalence (RSE) and Verghese's Strong
Equivalence (str.eq.). Both preserve finite and infinite
frequency system structure. RSE is over restrictive in
that it is constrained to act between systems of the same
dimension. While overcoming this basic difficulty str.eq.
on the other hand has no closed form description. In this
work all these difficulties have been overcome. A constant
pencil transformation termed Complete Equivalence (CE) is
proposed, this preserves finite elementary divisors and
non-unity infinite elementary divisors. Applied to GSS
systems CE yields Complete System Equivalence (CSE)
which is shown to be a closed form description of str.eq.
and is more general than RSE as it relates systems of
different dimensions.
Equivalence can be described in terms of mappings of the
solution sets of the describing differential equations
together with mappings of the constrained initial
conditions. This provides a conceptually pleasing
definition of equivalence. The new equivalence is termed
Fundamental Equivalence (FE) and CSE is shown to be a
matrix characterisation of it.
A polynomial system matrix transformation termed Full
Equivalence (fll.e.) is proposed. This relates general
matrix polynomials of different dimensions while preserving
finite and infinite frequency structure. A definition of
infinite zeros is also proposed along with a generalisation
of the concept of infinite elementary divisors (IED) from
matrix pencils to general polynomial matrices. The IED provide an additional method of dealing with infinite zeros
Self-tuning controllers via the state space
Imperial Users onl
Implementation of self-tuning control for turbine generators
PhD ThesisThis thesis documents the work that has been done towards the development of
a 'practical' self-tuning controller for turbine generator plant. It has been shown
by simulation studies and practical investigations using a micro-alternator system
that a significant enhancement in the overall performance in terms of control and
stability can be achieved by improving the primary controls of a turbine generator
using self-tuning control.
The self-tuning AVR is based on the Generalised Predictive Control strategy. The
design of the controller has been done using standard off-the-shelf microprocessor
hardware and structured software design techniques. The proposed design is thus
flexible, cost-effective, and readily applicable to 'real' generating plant. Several
practical issues have been tackled during the design of the self-tuning controller and
techniques to improve the robustness of the measurement system, controller, and
parameter estimator have been proposed and evaluated. A simple and robust
measurement system for plant variables based on software techniques has been
developed and its suitability for use in the self-tuning controller has been practically
verified. The convergence, adaptability, and robustness aspects of the parameter
estimator have been evaluated and shown to be suitable for long-term operation in
'real' self-tuning controllers.
The self-tuning AVR has been extensively evaluated under normal and fault
conditions of the turbine generator. It has been shown that this new controller is
superior in performance when compared with a conventional lag-lead type of
fixed-parameter digital AVR. The use of electrical power as a supplementary
feedback signal in the new AVR is shown to further improve the dynamic stability
of the system.
The self-tuning AVR has been extended to a multivariable integrated self-tuning
controller which combines the AVR and EHG functions. The flexibility of the new
AVR to enable its expansion for more complex control applications has thus been
demonstrated. Simple techniques to incorporate constraints on control inputs
without upsetting the loop decoupling property of the multivariable controller have
been proposed and evaluated. It is shown that a further improvement in control
performance and stability can be achieved by the integrated controller.Parsons Turbine Generators Ltd
Model structure selection using an integrated forward orthogonal search algorithm assisted by squared correlation and mutual information
Model structure selection plays a key role in non-linear system identification. The first step in non-linear system identification is to determine which model terms should be included in the model. Once significant model terms have been determined, a model selection criterion can then be applied to select a suitable model subset. The well known Orthogonal Least Squares (OLS) type algorithms are one of the most efficient and commonly used techniques for model structure selection. However, it has been observed that the OLS type algorithms may occasionally select incorrect model terms or yield a redundant model subset in the presence of particular noise structures or input signals. A very efficient Integrated Forward Orthogonal Search (IFOS) algorithm, which is assisted by the squared correlation and mutual information, and which incorporates a Generalised Cross-Validation (GCV) criterion and hypothesis tests, is introduced to overcome these limitations in model structure selection
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Generalised resultants, dynamic polynomial combinants and the minimal design problem
The theory of dynamic polynomial combinants is linked to the linear part of the dynamic determinantal assignment problems (DAP), which provides the unifying description of the dynamic, as well as static pole and zero dynamic assignment problems in linear systems. The assignability of spectrum of polynomial combinants provides necessary conditions for solution of the original DAP. This paper demonstrates the origin of dynamic polynomial combinants from linear systems, examines issues of their representation and the parameterisation of dynamic polynomial combinants according to the notions of order and degree, and examines their spectral assignment. Central to this study is the link of dynamic combinants to the theory of generalised resultants, which provide the matrix representation of the dynamic combinants. The paper considers the case of coprime set of polynomials for which spectral assignability is always feasible and provides a complete characterisation of all assignable combinants with order above and below the Sylvester order. A complete parameterisation of combinants and respective generalised resultants is given and this leads naturally to the characterisation of the minimal degree and order combinant for which spectrum assignability may be achieved, which is referred to as the dynamic combinant minimal design (DCMD) problem. An algorithmic approach based on rank tests of Sylvester matrices is given, which produces the minimal order and degree solution in a finite number of steps. Such solutions provide low bounds for the respective dynamic assignment control problems
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Structure assignment problems in linear systems: Algebraic and geometric methods
The Determinantal Assignment Problem (DAP) is a family of synthesis methods that has emerged as the abstract formulation of pole, zero assignment of linear systems. This unifies the study of frequency assignment problems of multivariable systems under constant, dynamic centralized, or decentralized control structure. The DAP approach is relying on exterior algebra and introduces new system invariants of rational vector spaces, the Grassmann vectors and PlĂĽcker matrices. The approach can handle both generic and non-generic cases, provides solvability conditions, enables the structuring of decentralisation schemes using structural indicators and leads to a novel computational framework based on the technique of Global Linearisation. DAP introduces a new approach for the computation of exact solutions, as well as approximate solutions, when exact solutions do not exist using new results for the solution of exterior equations. The paper provides a review of the tools, concepts and results of the DAP framework and a research agenda based on open problems
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