Showing papers on "Control theory published in 1998"

Sliding mode control : theory and applications

Abstract: In the formation of any control problem there will be discrepancies between the actual plant and the mathematical model for controller design. Sliding mode control theory seeks to produce controllers to over some such mismatches. This text provides the reader with a grounding in sliding mode control and is appropriate for the graduate with a basic knowledge of classical control theory and some knowledge of state-space methods. From this basis, more advanced theoretical results are developed. Two industrial case studies, which present the results of sliding mode controller implementations, are used to illustrate the successful practical application theory.

Current control techniques for three-phase voltage-source PWM converters: a survey

Abstract: The aim of this paper is to present a review of current control techniques for three-phase voltage-source pulsewidth modulated converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes proportional integral (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on-line optimization. New trends in current control-neural networks and fuzzy-logic-based controllers-are discussed, as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.

A unified framework for hybrid control: model and optimal control theory

Abstract: We propose a very general framework that systematizes the notion of a hybrid system, combining differential equations and automata, governed by a hybrid controller that issues continuous-variable commands and makes logical decisions. We first identify the phenomena that arise in real-world hybrid systems. Then, we introduce a mathematical model of hybrid systems as interacting collections of dynamical systems, evolving on continuous-variable state spaces and subject to continuous controls and discrete transitions. The model captures the identified phenomena, subsumes previous models, yet retains enough structure to pose and solve meaningful control problems. We develop a theory for synthesizing hybrid controllers for hybrid plants in all optimal control framework. In particular, we demonstrate the existence of optimal (relaxed) and near-optimal (precise) controls and derive "generalized quasi-variational inequalities" that the associated value function satisfies. We summarize algorithms for solving these inequalities based on a generalized Bellman equation, impulse control, and linear programming.

Iterative feedback tuning: theory and applications

Abstract: We have examined an optimization approach to iterative control design. The important ingredient is that the gradient of the design criterion is computed from measured closed loop data. The approach is thus not model-based. The scheme converges to a stationary point of the design criterion under the assumption of boundedness of the signals in the loop. From a practical viewpoint, the scheme offers several advantages. It is straightforward to apply. It is possible to control the rate of change of the controller in each iteration. The objective can be manipulated between iterations in order to tighten or loosen performance requirements. Certain frequency regions can be emphasized if desired. This direct optimal tuning algorithm is particularly well suited for the tuning of the basic control loops in the process industry, which are typically PID loops. These primary loops are often very badly tuned, making the application of more advanced (for example, multivariable) techniques rather useless. A first requirement in the successful application of advanced control techniques is that the primary loops be tuned properly. This new technique appears to be a very practical way of doing this, with an almost automatic procedure.

Control of a nonholonomic mobile robot using neural networks

Abstract: A control structure that makes possible the integration of a kinematic controller and a neural network (NN) computed-torque controller for nonholonomic mobile robots is presented. A combined kinematic/torque control law is developed using backstepping and stability is guaranteed by Lyapunov theory. This control algorithm can be applied to the three basic nonholonomic navigation problems: tracking a reference trajectory, path following, and stabilization about a desired posture. Moreover, the NN controller proposed in this work can deal with unmodeled bounded disturbances and/or unstructured unmodeled dynamics in the vehicle. Online NN weight tuning algorithms do not require off-line learning yet guarantee small tracking errors and bounded control signals are utilized.

Comparison of current control techniques for active filter applications

Abstract: This paper presents the comparative evaluation of the performance of three state-of-the-art current control techniques for active filters. The linear rotating frame current controller, the fixed-frequency hysteresis controller, and the digital deadbeat controller are considered. The main control innovations, determined by industrial applications, are presented, suitable criteria for the comparison are identified, and the differences in the performance of the three controllers in a typical parallel active filter setup are investigated by simulations.

Advantages of switched reluctance motor applications to EV and HEV: design and control issues

Abstract: Land vehicles need their drivetrain to operate entirely in constant power in order to meet their operational constraints, such as initial acceleration and gradability, with minimum power rating. The internal combustion engine (ICE) is inappropriate for producing this torque-speed profile. Therefore, multiple gear transmission is necessary with the ICE in a vehicle. Some electric machines, if designed and controlled appropriately, are capable of producing an extended constant power range. The purpose of this paper is to investigate the capabilities of the switched reluctance motor (SRM) for electric vehicle and hybrid electric vehicle applications. This investigation is carried out in two steps. The first step involves the machine design and the finite-element analysis to obtain the static characteristic of the motor. In the second step, the finite-element field solutions are used in the development of a nonlinear model to investigate the dynamic performance of the designed motor.

Stability analysis and design of fuzzy control systems

Abstract: The stability of a fuzzy feedback control system consisting of a fuzzy controller connected in series with a plant described by a fuzzy model is discussed. The stability analysis is based on some new theorems that guarantee sufficient conditions for asymptotical stability of the equilibrium point and total stability of the system. The stability analysis results are used to provide an approach to fuzzy controller design. The steps of the approach are specified through a design example.

Adaptive Control

Abstract: From the Publisher: Adaptive Control provides techniques for automatic adjustment in real time of controller parameters to achieve or maintain a desired level of system performance when the process parameters are unknown or variable. The book deals coherently with many aspects of the field, starting with the problems posed and moving onto the presentation of the solutions and their practical significance. As well as presenting recent trends, the book also looks at: Synthesis and Analysis of Parameter Adaptation Algorithms, Recursive Plant Model Identification in Open and Close Loop, Robust Digital Control for Adaptive Control, Robust Parameter Adaptation Algorithms, Direct and Indirect Adaptive Control, and Practical Aspects and Applications. To reflect the importance of digital computers for the application of adaptive control techniques, discrete-time aspects are emphasized. To guide the reader, the book contains various applications of adaptive control techniques.

Universal tactile feedback system for computer video games and simulations

Abstract: A universal tactile feedback system for comptuer and video game systems which provides real time tactile feedback. The system includes a microcontroller based circuit that can operate in either a host-independent or a host-dependent mode. The host-independent mode is responsive to an audio signal which is typically generated by a computer while it is executing a game. The digital post-processing utilizes an algorithm with reprogrammable parameters that can be uniquely set for any given game or simulation. After the audio signal is processed, the results are used to generate multiple independent control signals for multiple independent tactile sensation generators (510, 520, 530, 540, 535, 545, 550, 560, 570, 575, 585, 595 and 598). Alternatively, the host-dependent mode is directly responsive to control commands generated by a computer while it is executing a game. All reconfigurable parameters are reprogrammable in real time by sending a communication to the controller (110) via any typical digital I/O port. The system's tactile sensation generators include independent groups of one or more actuators that are embedded within or attached to various devices.

Verified hybrid controllers for automated vehicles

Abstract: The objective of an automated highway system (AHS) is to increase the safety and throughput of the existing highway infrastructure by introducing traffic automation. AHS is an example of a large scale, multiagent complex dynamical system and is ideally suited for a hierarchical hybrid controller. We discuss the design of safe and efficient hybrid controllers for regulation of vehicles on an AHS. We use game theoretic techniques to deal with the multiagent and multiobjective nature of the problem. The result is a hybrid controller that by design guarantees safety, without the need for further verification. The calculations also provide an upper bound on the performance that can be expected in terms of throughput at various levels of centralization.

Servo controller in scanner of image formation device

Abstract: PROBLEM TO BE SOLVED: To provide a scanner controller of an image formation device which automatically changes the direction of the motor current and provides a rapid and proper scanner travelling performance, when a difference between the motor current and a control target current value at the time of speed reduction in the return operation of the scanner is large. SOLUTION: In an image formation device, a scanner for reading the image data from an original image is reciprocated by a motor M31. A servo controller is constituted of an H-bridge circuit, which rotates the motor in the forward and the reverse direction from a PWM(pulse width modulation) signal which determines the motor speed and a signal determining the direction of rotation, an encoder EC31 installed on a motor shaft, a microcomputer 30 which detects the speed of the rotation and calculates the speed, and controls the speed of the motor from a detection signal of the encoder, a detecting section 40 which detects the value and direction of current in the motor, and a feedback system which controls the speed from the deviation of the motor current value from a target command current value, obtained form the calculation of the motor speed and determines the direction of current to be allowed to flow in the motor from the comparison result between the motor current value and the target command current value and then controls the direction of rotation of the motor.

Trajectory Tracking for Autonomous Vehicles: An Integrated Approach to Guidance and Control

Abstract: . This paper addresses the problem of in- tegrated design of guidance and control systems for au- tonomous vehicles (AVs). In fact, it introduces a new methodology for integrated design of guidance and control for such vehicles. The methodology proposed leads to an efficient procedure for the design of controllers for AVs to accurately track reference trajectories defined in an iner- tia! reference frame. The paper illustrates the application of this procedure on the design of a tracking controller for the Unmanned Air Vehicle Bluebird. The design phase is summarized, and the performance of the resulting con- troller is assessed in simulation using dynamic models of the vehicle and its sensor suite.

Variable supply-voltage scheme for low-power high-speed CMOS digital design

Abstract: This paper describes a variable supply-voltage (VS) scheme. From an external supply, the VS scheme automatically generates minimum internal supply voltages by feedback control of a buck converter, a speed detector, and a timing controller so that they meet the demand on its operation frequency. A 32-b RISC core processor is developed in a 0.4-/spl mu/m CMOS technology which optimally controls the internal supple voltages with the VS scheme and the threshold voltages through substrate bias control. Performance in MIPS/W is improved by a factor of more than two compared with its conventional CMOS design.

PID controller tuning for desired closed‐loop responses for SI/SO systems

Abstract: Proportional integral, and derivative (PID) parameters are obtained for general process models by approximating the feedback form of an IMC controller with a Maclaurin series in the Laplace variable. These PID parameters yield closed-loop responses that are closer to the desired responses than those obtained by PID controllers tuned by other methods. The improvement in closed-loop control performance becomes more prominent as the dead time of the process model increases. A new design method for two degree of freedom controllers is also proposed. Such controllers are essential for unstable processes and provide significantly improved dynamic performance over single degree of freedom controllers for stable processes when the disturbances enter through the process.

Toward improvement of tracking performance nonlinear feedback for linear systems

Abstract: A composite nonlinear feedback tracking control law based on a nominal linear controller is proposed. The design yields nonlinear feedback laws that both increase the speed of the closed-loop system response to the command input and reduce the overshoot, while not imperilling the small signal performance achieved by the nominal linear feedback controller in the face of actuator amplitude saturation. A modern flight control application is used to demonstrate the effectiveness of the design.

Fast optical and process proximity correction algorithms for integrated circuit manufacturing

Abstract: In this thesis, we first look at the Optical Proximity Correction (OPC) problem and define the goals, constraints, and techniques available. Then, a practical and general OPC framework is built up using concepts from linear systems, control theory, and computational geometry. A simulation-based, or model-based, OPC algorithm is developed which simulates the optics and processing steps of lithography for millions of locations. The key contributions to the OPC field made in this thesis work include: (1) formulation of OPC as a feedback control problem using an iterative solution, (2) an algorithm for edge movement during OPC with cost function criteria, (3) use of fast aerial image simulation for OPC, which truly enables full chip model-based OPC, and (4) the variable threshold resist (VTR) model for simplified prediction of CD based off aerial image. A major contribution of this thesis is the development of a fast aerial image simulator which is tailored to the problem of OPC. In OPC applications, it is best to compute intensity at sparse points. Therefore, our fast aerial image simulator is tailored to computing intensity at sparse points, rather than on a regular dense grid. The starting point for the fast simulation is an established decomposition of the Hopkins partially coherent imaging equations, originally proposed by Gamo (14). Within this thesis, the decomposition is called the Sum of Coherent Systems (SOCS) structure. The numerical implementation of this decomposition using Singular Value Decomposition (SVD) is described in detail. Another contribution of this thesis is the development of a variable threshold resist model (VTR). The model uses the aerial image peak intensity and image slope along a cutline to deduce the development point of the resist, and has two primary benefits: (1) it is fast, (2) it can be fit to empirical data. We combine the fast aerial image simulator and the VTR model in an iterative feedback loop to formulate OPC as a feedback control problem. (Abstract shortened by UMI.)

Active diagnosis of discrete-event systems

Abstract: The need for accurate and timely diagnosis of system failures and the advantages of automated diagnostic systems are well appreciated. However, diagnosability considerations are often not explicitly taken into account in the system design. In particular, design of the controller and that of the diagnostic subsystem are decoupled, and this may significantly affect the diagnosability properties of a system. The authors present an integrated approach to control and diagnosis. More specifically, they present an approach for the design of diagnosable systems by appropriate design of the system controller. This problem, which they refer to as the active diagnosis problem, is studied in the framework of discrete-event systems (DESs); it is based on prior and new results on the theory of diagnosis for DESs and on existing results in supervisory control under partial observations. They formulate the active diagnosis problem as a supervisory control problem where the legal language is an "appropriate" regular sublanguage of the regular language generated by the system. They present an iterative procedure for determining the supremal controllable, observable, and diagnosable sublanguage of the legal language and for obtaining the supervisor that synthesizes this language. This procedure provides both a controller that ensures diagnosability of the closed-loop system and a diagnoser for online failure diagnosis. The procedure can be implemented using finite-state machines and is guaranteed to converge in a finite number of iterations. The authors illustrate their approach using a simple pump-valve system.

Biped robot walking using gravity-compensated inverted pendulum mode and computed torque control

Abstract: This paper proposes a model called the gravity-compensated inverted pendulum mode (GCIPM) to generate a biped locomotion pattern that is similar to the one generated by the linear inverted pendulum mode, but accommodates the free leg dynamics based upon its predetermined trajectory. When the biped locomotion based upon the linear inverted pendulum mode is applied to real biped robots, the stability of the robot is disturbed due to the fact that the neglected dynamics of free legs is not actually negligible, moving the ZMP (zero moment point) away from the presumed fixed point. The GCIPM includes the effect of the dynamics of the free leg in a simple manner This paper also presents a control method for biped robots based upon the computed torque. Simulation results show that the biped robot is more stable with the walking pattern generated by the proposed method combined with the controller than with the one by the inverted pendulum mode.

Adaptive controller design for tracking and disturbance attenuation in parametric strict-feedback nonlinear systems

Abstract: The authors develop a systematic procedure for obtaining robust adaptive controllers that achieve asymptotic tracking and disturbance attenuation for a class of nonlinear systems which are described in the parametric strict-feedback form and are subject to additional exogenous disturbance inputs. Their approach to adaptive control is performance-based, where the objective for the controller design is not only to find an adaptive controller, but also to construct an appropriate cost functional, compatible with desired asymptotic tracking and disturbance attenuation specifications, with respect to which the adaptive controller is "worst case optimal". Three main issues of the paper are: the backstepping methodology, worst case identification schemes, and singular perturbations analysis. Closed-form expressions have been obtained for an adaptive controller and the corresponding value function. A numerical example involving a third-order system is given.