Computer-aided Control System Design Package Research Articles

The State of the Art in CACSD a Decade after Ecstasy

In the mid 1980s, the UK Science and Engineering Research Council funded a number of projects to develop computer-aided control system design (CACSD) environments. The flagship project was ECSTASY (Environment for Control System Theory and SYnthesis), a database-mediated framework for hosting a number of popular control systems design tools. As the ECSTASY project neared its completion, some of the most urgently requested features appeared in rival commercial packages, and the short-falls in tool provision that ECSTASY was designed to address apparently went away. Using as a benchmark the capabilities of the current generation of the popular CACSD package MATLAB, the prescience of the original ECSTASY proposal will be demonstrated. A couple of areas that the environment excelled in, the use of a common information model and common user interface, will be discussed in the context of recent work done in the University of Wales and elsewhere. Finally, two topics of particular interest to the authors, the proposed standard reference model for computer-aided control engineering and an Object-Oriented Unified Infonnation Model for CACSD will be revisited in the light of recent developments in internet computing.

Experimental physical parameter estimation of a thyristor driven DC-motor using the HMF-method

This paper deals with the physical parameter estimation of the nonlinear continuous-time dynamics of a thyristor-driven dc-motor experimental set-up using the Hartley modulating functions (HMF) method. The approach applies a frequency-weighted leastsquares formulation to estimate the nonlinear continuous-time system parameters based on input-output data records over a finite time interval. The laboratory experimental set-up of the plant is facilitated by a computer-aided control system design software system, CADACS. The method has given satisfactory experimental results, and demonstrates its feasibility for use in parameter estimation of physically-based continuous-time systems. Due to its encouraging results, further studies will continue, in order to implement the methodology in the form of batch scheme recursive estimation for nonlinear continuous-time dynamics.

Parameter Estimation of the Nonlinear Dynamics of a Thyristor Driven DC-Motor Experimental Set-Up Using HMF-Method

The application of the Hartley modulating functions (HMF) method to estimate parameters of a thyristor driven dc-motor laboratory experimental set-up is investigated. The HMF-method is well suited for the parameter estimation of physically-based continuous-time nonlinear systems from their I/O-data records. This recently developed methodology uses a frequency dependent weighted least squares algorithm. The practical implementation of the HMF-method is facilitated by the computer-aided control system design software CADACS. The inputs of the dc-motor system are set from the personal computer CADACS software through D/A converters and the I/O-responses are displayed on the analog instruments as well as on the PC screen via A/D converters. Then, the I/O-data are applied to a suitable HMF-algorithm of the dc-motor model to estimate the physically-based system parameters. The practical application of the HMF-method and here obtained good results demonstrate the efficiency of this new approach.

Approximations for Quantitative Feedback Theory Designs

The computational requirements for obtaining the results summarized in the preceding section were very modest and were easily accomplished using computer-aided control system design software. Of special significance is the ability of the PDT to indicate a loop closure sequence for MIMO QFT designs that employ sequential loop closure. Although discussed as part of a 2 x 2 design, the PDT is obviously applicable to designs with a greater number of inputs and system responses.

Parallel computing in CACSD

Computer-aided design of control systems via multiobjective optimisation is a computationally demanding task that may benefit from parallel processing techniques. In this paper, we report on a new parallel processing gateway that supports the use of parallel processing within the framework of an existing computer-aided control system design software package. In many control system design exercises which employ optimisation, the bulk of the computational effort is devoted to the evaluation of the objectives of the optimisation at each iteration. This paper demonstrates, with an example, how, using the gateway, parallel processing can be used within the framework of existing computer-aided control system design tools to compute these objective values.

Knowledge-Based Interfaces to a Computer-aided Control System Design Package

Design of automatic control systems is a computationally intensive process. This motivates the development of accessible, easily usable and shareable interactive computing environment incorporating specialized knowledge of the theory and codified practice of automatic control. Expert and knowledge based systems play key role in creation of such environment. The expert system techniques can be used for the design of control systems. SFPACK is a special purpose interactive computer language for control system design. One feature of this package is that it incorporates an expert system development facility called DECESS. This expert system development facility can be used to design controllers for linear multivariable control systems. This paper describes an object-oriented knowledge interface to SFPACK. SFPACK has been used as a teachware for presenting techniques in control system design. The package runs on a SUN workstation or VAX machines and has been used successfully in a course on control engineering at the graduate level.

Computer-aided design and analysis of linear multivariable control systems using the systematic design approach

A new approach for the design of multivariable feedback control systems in the frequency domain is presented. The techniques handle stability, performance, and robustness aspects of the design problem satisfactorily. The overall approach is systematic and intuitively appealing. A new computer-aided control system design package called SFPACK is developed. This package has implemented the new frequency response design techniques. The package is interactive and command-driven, and it is used as a teaching tool for helping the students to understand the concepts of the design approach. The MAT-LAB-derived control environment in SFPACK is extended to provide the user with an expert system development environment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Solutions of the second benchmark control problem

A report is presented on the results of the second benchmark control problem prepared by the Benchmark Working Group of the IEEE Control Systems Society Technical Committee on computer-aided control system design (CACSD). The problem deals with a continuous-time missile autopilot design. The purpose of this benchmark is to provide a useful measure of some of the capabilities of computer-aided control system design packages. The problem requires time simulations, eigenvalue calculations, and frequency-response plots of relatively high-order linear systems. The problem is described, and the results submitted to date are summarized. >

Computer-aided design and analysis for a class of nonlinear systems

A description is given of a computer-aided control system design package, NLCON, that supports analysis and design functions for single-input/single-output nonlinear control systems with a single nonlinearity. The single nonlinearity can be one of seven nonlinearities commonly encountered in mechanical systems, and its location within the system is not restricted. The controller design benefits from designer experience, but it is facilitated by the software package, since program operation is highly interactive and the interface is user friendly. The analysis functions supported include sinusoidal-input describing functions and limit-cycle analysis, frequency-response determination, and jump-resonance analysis. Design functions include procedures for compensator modification to modify limit-cycle and jump-resonance behavior. A design advisory is provided for some simple design situations. Examples to illustrate various facets of program operation are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Teaching multivariable control with CADCS packages and PCs

A first multivariable control experiment is described for the teaching of control. The different processes which can be used in the experiment are simulated with inexpensive analog components. Computer aided control system design packages (CADCS) are used extensively to derive controllers for these multivariable processes. The designed controllers are initially simulated in closed-loop form using CADCS packages with interactive graphics, and then implemented on IBM PC compatibles to verify their effectiveness in the control of the analog processes. Important phenomena such as multivariable interaction, actuator and process saturation, limit cycling, and reachability are brought out as the students are conducted through the process of controller design and evaluation. Experimental results are given from a typical teaching laboratory exercise on one of the processes.

Software and laboratory experiments using computers in control education

The use of computers for classroom presentations, exercises, laboratory experiments, and in projects is discussed. Commercially available simulation and computer-aided control system design packages can be used in teaching together with real-time software and with special programs developed for specific purposes. These possibilities are illustrated by citing many examples of learning and teaching control systems with computers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A LQG CACSD Package and its Application

A Computer Aided Control System Design (CACSD) package for the design of multivariable control systems using the optimal linear Quadratic (LQ) and the linear Quadratic Gaussian (LQG) paradigm is presented. The LQ/LQG techniques provides a complete multivariable design and synthesis theory. The growth in the number of industrial, marine and aerospace applications has encouraged this research activity. This paper is concerned with the LQG CACSD package development, the application of design techniques and the solution of real practical design problems.

Computer Aided Control System Design Software in Process Control — A Survey

The field of Computer Aided Control System Design (CACSD) has developed rapidly during the past decade. In this paper a survey is presented of the current state of software for this field. Software packages are classified according to the aspect of the control system design process addressed by the package. An analysis of the existing status examines reasons for the limited acceptance of this technology in industrial process control practice. A strong need for an integrated computer aided engineering environment is identified and this is discussed in more detail. With the growing interest in artificial intelligence and expert systems in mind, the potential impact of these technologies on CACSD software is examined. Finally some consideration is given to newly available hardware and speculations made about future directions of CACSD.

A research group's CACSD environment

The paper describes the recent development of the computer-aided control system design (CACSD) facilities within the Industrial Control Unit (ICU) at the University of Strathclyde. The PC environment now represents the most cost-effective choice in providing the control engineer with access to a powerful range of design facilities. CACSD packages are becoming popular as teaching aids, and show great potential for helping in the dissemination of new theoretical ideas to industry.

A graphical pre-processor for computer-aided control system design

Features in the design of a graphical man-machine interface for pre-processing the inputs to computer-aided control system design software are described in this paper. The primary objective is to allow the control engineer to communicate with a modem graphics workstation in a natural, familiar and friendly way, by means of block diagrams, signal flow graphs and standard mathematical text. Graphical methods for the input and output of these are described. Transformations between different system descriptions are considered which allow all algebraic manipulations and reductions to be performed on signal flow graphs. For these manipulations, rule-based methods are shown to be effective. The possibility of using symbolic computation languages for algebraic operations is also considered.

Computer-aided Control System Design (CACSD): Some Perspectives

Publisher Summary This chapter discusses Computer-Aided Control System Design (CACSD) and its prospects in the field of control engineering. The accelerating interest in CACSD is closely related to developments in many other disciplines, including aspects of computer hardware and software, numerical analysis, optimization and most importantly, control theory itself. The control systems designer has in general a unique class of problems to solve and a large box of tools to draw upon, and in this sense the issues to be addressed in CACSD are quite distinct from those in general computer-aided designs (CADs). The Linear-Quadratic-Gaussian (LQD) design methodology, which has evolved in both mathematical content and computational algorithms, is the most general time domain approach presently available for determining multivariable control laws. CACSD packages are designed to solve these problems. Software systems to perform all the steps in the control design cycle starting from system modeling to data analysis, identification, control synthesis and simulation have been recently reported. These packages claim features such as power matrix interpreters, user-friendly environment with device independent graphics, state-of-the-art numerical algorithms for reliable computations, and user-transparent file management.

The development of a graphical man-machine interface for computer-aided control system design

In this paper we describe features in the design of a graphical man-machine interface for preprocessing the inputs to computer-aided control system design software. The primary objective is to allow the control engineer to communicate with a modem graphics workstation in a natural, familiar and friendly way, by means of block diagrams, signal flow graphs and standard mathematical text. Graphical methods for the input and output of these are described. Transformations between different system descriptions are considered which allow all algebraic manipulations and reductions to be performed on signal flow graphs. For these manipulations, rule-based methods are shown to be effective. The possibility of using symbolic computation languages for algebraic operations is also considered.

Two tutorial examples of multivariable control system design

Two tutorial examples are presented which illustrate different methods of designing practical multivariable control systems using frequency-domain techniques. In the first case eigen vector alignment techniques are used to manipulate and shape the generalised Nyquist diagrams, while in the second case LQG theory in conjunction with singular value plots is employed. In both cases the designs are carried out on a modern computer-aided control-system design package.

Future directions in computer-aided control system design software development

Issues in the development of a new package of computer-aided control system design software are presented. The scope of the project is limited to the organization of existing results into a unified body of software, and the development of a standardized set of tools and services which allow long-term maintenance and growth of the package and support the user community. Issues which influence language selection, graphics requirements, core algorithm selection, model description requirements and software tools, and future hardware expectations are addressed.

Computer-aided multivariable control system design for processes with time delays

A computer-aided control system design package is described which handles processes with multiple time delays and allows subsequent design of interaction compensators. The package synthesizes control system designs for complex problems in a short time while also providing dynamic simulation for the purpose of evaluating controller performance. Example problems are presented along with a case study on sensitivity to errors in the delays.