Control Design Specifications Research Articles

Robust H∞/µ Control Design for an Inverted Pendulum

This paper presents a case study of a robust H∞/µ controller synthesis of an inverted pendulum device. It illustrates different selection strategies for the performance and robust controller design specifications. The effects of disturbance and uncertain components on performance outputs of the plant are minimized in the H∞ sense. In the case of an inverted pendulum, the designed H∞ controller fulfills the predefined robust stability requirement, however, it does not fulfill the pre-defined performance requirement. In the μ-synthesis, the enhancement of the controller can be achieved taking the structured singular values into consideration. Applying D-K iteration for an inverted pendulum, the designed controller guarantees both the robust stability and the robust performance.

Quantitative feedback design for a variable-displacement hydraulic vane pump

In this paper the model development, problem specification, constraint formulation, and optimal feedback controller design for a variable-displacement hydraulic pump system are shown using the Quantitative Feedback Theory (QFT) technique. The use of variable-displacement pumps in hydraulic system applications has become widespread due to their efficiency advantages; however, this efficiency gain is often accompanied by a degradation of system stability. Here we develop a QFT controller for a variable-displacement pump based upon a linear, parametrically uncertain model in which some of this uncertainty reflects variation in operating point-dependent parameters. After presentation of a realistic non-linear differential equation model, the linearized model is developed and the effect of parametric uncertainty is reviewed. From this point, closed-loop performance specifications are formulated and the QFT design technique is carried out. An initial feasible controller is designed, and this design is optimized via a non-linear programming technique. In conclusion, a non-linear closed-loop system response is simulated. This paper is intended to have tutorial value, both in terms of the detailed hydraulic system model development, as well as in terms of the detailed exposition of the QFT controller design and optimal loop shaping processes. © 1998 John Wiley & Sons, Ltd.

Stability and integrity enforcement by integrating variable pairing and controller design

The Relative Gain Array (RGA) and the Niederlinski Index (NI) represent powerful tools for variable pairings selection to achieve minimum interaction subject to stability and integrity in decentralized control systems. Nevertheless, closed-loop integrity of the highest priority (against single loop failure) can not be guaranteed by variable pairing choice only, particularly when pairing on negative RGA elements becomes inevitable for a given process. In parallel to the Generalized Niederlinski Index (GNI), a generalized integrity criterion based on steady state information of both the process and the controller is developed. Both the GNI and the generalized integrity criterion allow for joint consideration of variable pairing selection and controller design and reduce to the NI and RGA rules, thus representing more general tools than the NI and RGA for simultaneously ensuring closed-loop stability and integrity in decentralized control systems. The new criteria are particularly useful when it is impossible to find a pairing corresponding to all RGA elements positive. Guidelines for integrating variable pairing and controller design are offered. The inclusion of controller design imposes no considerable difficulty, since only directional change of individual controllers is important with no specific controller design actually required.

H∞ robust control design for dynamic ship positioning

Prerequisites to the successful application of the H∞ control design technique to the marine dynamic positioning (DP) control problem are a realistic nominal model, relative bounds on modelling uncertainty, a set of frequency-dependent weighting functions to translate the control design specification into a control solution and a performance index to quantify the robustness. The authors propose procedures and algorithms to achieve these objectives. The H∞ robust control design technique is then used to calculate a robust controller which has superior properties to the conventional DP systems. The trade-off between track keeping and station keeping is undertaken via appropriate weighting functions and a two-degree-of-freedom control structure is employed. The technique proposed shows that effective wave filtering can be obtained with guaranteed stability robustness. The advantage of the proposed control design technique is demonstrated using ship nonlinear simulations.

An Isolated Structural System Using Localized Vibration Control

This paper describes an approach to actively isolate vibration of a complex structural system by controlling six degrees of freedom in its support areas. The controller attempts to stabilize only localized areas near where the structure is supported rather than attempting to stabilize the entire structure. Actuator/sensor placement and model reduction are discussed, and the specific controller design and performance measure are described. The relative performance levels of different control strategies are evaluated by examining a frequency-dependent disturbance rejection property. Concepts are illustrated by numerically simulating a complex structural system comprising a flat plate supported by two box girders; plant dynamics are obtained from a finite-element model. Conclusions are drawn regarding the mechanisms by which localized vibration control is exerted.

Robustly stable active structural control

AbstractDue to various model uncertainties, most existing control strategies may lead to arbitrarily small stability margins. This paper presents an H2/H2 nested control synthesis which combines advantages of the classical H2 and H2‐approaches, and guarantees robust stability. Special H2‐maximum and H2‐ultimate system norms are introduced by generalizing the concept of the standard L1, H2 and H2 norms. These norms reduce the conservatism of the control design specifications while retaining all the benefits of the standard H2‐norm. Both stochastic and deterministic interpretations are addressed. The effectiveness of the new method is illustrated by a numerical example.

Robust control of an unknown plant—the IFAC 93 benchmark

Many control design specifications, such as the IFAC 1993 benchmark, include stringent closed-loop performance requirements, which are required to be met in the face of uncertainties. Such problems can be effectively designed by a combination of the method of inequalities, which designs for explicit closed-loop performance, and analytical optimization techniques, from which robustness is obtained. This paper describes how to combine the method of inequalities with a variety of analytical optimization methods. An introduction to μ synthesis is also included. The design of robust controllers for the benchmark problem using these methods is described, and a simple adaptive gain scheme to improve the performance is suggested.

Optimal control design for fast coordinate measuring machine

Abstract Coordinate Measuring Machines (CMM) are used in manufacturing processes for accurate and rapid inspection of machine products. High accuracy and high speed are two conflicting design requirement of the CMM control system. The CCM considered here consists of three orthogonal arms and a two Degree-Of-Freedom (DOF) probe. Unlike the conventional control system where the controlled variable is measured, the probe position measurement is not available. The objective of this paper is to develop an optimal CMM position controller such that the inspection time is minimised. A two Degree-Of-Freedom (DOF) optimal controller is developed to meet the position loop control design specification. The control solution is found using the polynomial approach. Simulation and experimental results show that the optimal controller can significantly reduce the probe position deviation and also minimise the positioning time.

Optimal Control Design for Fast Coordinate Measuring Machine

The objective of this paper is to develop an optimal position controller for fast Coordinate Measuring Machines (CMM) to minimise the inspection time. CMMs are used in manufacturing processes for accurate and rapid inspection of machine products. High accuracy and high speed are two conflicting design requirements of the CMM control system. Unlike the conventional control system where the controlled variable is measured, the end point measurement is not available. An optimal controller is developed using polynomial approach to meet the control design specification. Experimental results show that the optimal controller can significantly improve the accuracy and reduce the positioning time.

Study of pulp cooking control using the systems approach

Abstract Control of batch digesters for magnesium bisulphite pulp cooking is considered. The aim of the study is to obtain a systematic, as well as a systemic problem definition for the subsequent design of higher-level control algorithms. The method of analysis was taken from general systems theory; the general scheme of the systems approach has been adapted to the specific control design problem. Following this approach, first, the behaviour of the basic control algorithms was explored by computer simulation. Based on these preliminary results, a systemic representation of the overall control problem was obtained by defining the pulp cooking process and the basic control algorithms together as a system with three inputs and three outputs. Further, the input-output relations of the system were examined by simulation. The final results are given in the form of three diagrams representing the static responses of the object system to the step changes of a single input. The significance of these characteristics is discussed in terms of information needed for the next step of control design. In addition, the diagrams contain some strategic operational hints for better process management on the lower control level.

A practical guide to high-temperature alloys

The requirement for materials which can operate at ever-higher service temperatures continues. Corrosion problems are a limiting factor and have been countered by improvements in material compositions, coating procedures and fabrication techniques. Existing high-temperature alloys are reviewed, leading to a discussion of their performance in a variety of corrosion environments — oxidation, sulfidation, hot corrosion, fuel ash corrosion, carburisation and halogen attack are considered. Options are given for each environment but it is emphasised that material selection cannot be separated from consideration of other factors of the high-temperature system, including process control and better overall design specifications.

On multiple criteria stationary linear quadratic control

Multiple control criteria and design specifications are, in general, present in control systems design. In this study, all Pareto optimal solutions are characterized for a large class of multiple criteria stationary linear quadratic control problems in terms of associated scalar criterion linear quadratic control problem solutions based on a supporting hyperplane argument, and thus the results are fully constructive. This argument, which was used to establish these results, is believed to be new.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Simulation and Analysis Program for the Education in Automatic Control

A simulation and analysis program for the education of undergraduate students of automatic control was developed on a low cost microcomputer. A control loop with controlled system and governor is simulated by a digital algorithm. Four different controlled systems can be combined with five different governors. The behaviour of the closed loop control system is simulated in realtime by a difference equation. Type and parameters of the governors and also the set point value can be changed during simulation. System reaction on this variation can be observed by the on-line plot of the closed loop output signal. The simulation can be interrupted for a plot of the Bode-Diagram or the Nyquist frequency response locus to proof stability or controller design specifications.

Ellipsoidal Set-Theoretic Control Synthesis

A Set-Theoretic approach to solving control problems is presented for systems with control and state constraints which are subjected to input disturbances. The input disturbance is modeled as an unknown-but-bounded process. The constraints on the states and controls are treated explicitly. The primary objective is to construct a control system that uses only available control effort to insure nonviolation of the prespecified state constraints in the presence of the input disturbance. Since the constraints are treated directly, this technique yields a design that satisfies the constraints. The effectiveness of Set-Theoretic control synthesis is evaluated by means of an example and by comparison with a specific Linear-Quadratic Control design procedure.

A Bisection Break-Up Theory for Cluster Ions and Its Application to the Design of Mean Specific Size Controllers

The most important condition for additional heating of high temperature plasmas and refuelling of fusion reactors using energetic cluster ions is to give the proper energy to each constituent atom. This can be done by controlling their specific sizes and by accelerating the cluster ions by an appropriate voltage. A bisection break-up theory, in which cluster ions are assumed to be divided into two equal fragments by electrostatic repulsion arising from multiple ionization by electron impact is proposed for the first time. The purpose of this theory is to obtain the relation between the mean specific size and the electron current. The theory gives good agreement between the theoretical and the experimental values of the mean specific size of nitrogen cluster ions, demonstrating its applicability to the design of mean specific size controllers.