Control Design Issues Research Articles

Design issues of uplink media access control (MAC) protocols for multimedia traffic over DS-CDMA systems

We propose an efficient uplink media access control (MAC) protocol for a variable spreading gain interference-limited wideband CDMA system. It can, with high spectral efficiency, support both real-time traffic like speech and video and also nonreal-time data traffic based on packet transmission. The schemes for power allocation, joint scheduling, and transmission rate adaptation for nonreal time data traffic are designed as integrated parts of the MAC, working together to improve the system performance in terms of capacity and delay. With these associated resource management mechanisms, the performances of the MAC protocol with two different channel-allocation methods for real-time traffic are numerically compared. One is demanding channel allocation, and the other is reserve channel allocation, in which a certain bandwidth is reserved for concurrent real-time traffic.

Synthesis of nonlinear discrete control systems via time-delay affine Takagi-Sugeno fuzzy models

The affine Takagi-Sugeno (TS) fuzzy model played a more important role in nonlinear control because it can be used to approximate the nonlinear systems more than the homogeneous TS fuzzy models. Besides, it is known that the time delays exist in physical systems and the previous works did not consider the time delay effects in the analysis of affine TS fuzzy models. Hence a parallel distributed compensation based fuzzy controller design issue for discrete time-delay affine TS fuzzy models is considered in this paper. The time-delay effect is considered in the discrete affine TS fuzzy models and the stabilization issue is developed for the nonlinear time-delay systems. Finally, a numerical simulation for a time-delayed nonlinear truck-trailer system is given to show the applications of the present approach.

A student control competition through a remote robotics lab

The Automatic Control Telelab (ACT) laboratory at the University of Siena, Italy, has developed a new module called the student competition system. In the ACT module, students or groups of students compete to develop the best controller for a given remote process. The competition not only stimulates students' interest in control systems but also enhances learning by facilitating the understanding of practical control design issues.

TRACKING CONTROL FOR CONSTRAINED MONOTONE SYSTEMS

Tracking control of nonlinear systems subject to constraints on the input is a challenging issue in control design. Forcing saturation on a previously designed controller may in general lead to destabilization or at least result in performance losses. Hereby it is shown that for a certain class of nonlinear monotone systems it is possible to design a suitable static nonlinear output feedback which stabilizes the system and preserves stability under control saturation.

Impact Control in Hydraulic Actuators

Every manipulator contact task that begins with a transition from free motion to constraint motion may exhibit impacts that could drive the system unstable. Stabilization of manipulators during this transition is, therefore, an important issue in contact task control design. This paper presents a discontinuous controller to regulate the transition mode in hydraulic actuators. The controller, upon sensing a nonzero force, positions the actuator at the location where the force was sensed, thus, exerting minimal force on a nonmoving environment. The scheme does not require force or velocity feedback as they are difficult to measure throughout the short transition phase. Also, no knowledge about the environment or hydraulic parameters is required for control action. Due to the discontinuity of the control law, the control system is nonsmooth. First, the existence, continuation and uniqueness of Filippov’s solution to the system are proven. Next, the extension of Lyapunov stability theory to nonsmooth systems is employed to guarantee the global asymptotic convergence of the entire system’s state towards the equilibrium point. Complete dynamic characteristics of hydraulic functions and Hertz-type contact model are included in the stability analysis. Experiments are conducted to verify the practicality and effectiveness of the proposed controller. They include actuator collisions with hard and soft environments and with various approach velocities.

Controller Design Under Fuzzy Model Uncertainty VIA CSP

In this paper, the issue of controller design under fuzzy uncertainty is discussed. Fuzzy logic is used as a language in which to express an uncertain model, instead of as an universal approximator. The solution of a particular case posed as a constraint satisfaction problem is discussed.

Some critical implementation issues in iterative robust control design

Iterative control is an efficient methodology for the design of highly-performing controllers. In this paper, we discuss many implementation issues of a new iterative scheme which explicitly accounts for the presence of uncertainty. The developed iterative enables one to improve quickly the performance through subsequent steps, while preserving the robust stability of the closed-loop system.

Stability and switching control design issues for a class of discrete time hybrid systems

For the class of systems considered, necessary and sufficient stabilizability conditions are unknown. However, by considering the same systems with unknown but bounded exogenous disturbances, we give finitely computable conditions, sufficient for stabilizability without disturbances, yet necessary for stabilizability with disturbances.

PID control for a distributed system with a smart actuator

The emergence of distributed architectures based on smart components and fieldbus networks is promoting changes in proportional-integral-derivative (PID) controller design issues. This paper explores how PID control can benefit from smart actuator and fieldbus technologies. Firstly, this paper discusses a smart actuator scheme to improve the efficiency of PID controller retuning, as well as an implementation using a low-cost stepper-motor. Then, the smart actuator is applied to on-line adaptation of PID parameters using a standard pole-placement design method. Finally, experimental validation of the proposed approach is conducted using a controller area network (CAN) bus-based distributed architecture demonstrator.

A Standard Approach to Control Room Design

In the developed and developing countries most of our lives are dominated by electronic systems, whether these are for transportation, food distribution, supply of electricity or air transport. Each of these systems will require to be controlled and in most cases this will be exercised from a centralised node — a control room. Current, electronically based control rooms were preceded by mechanical ones — such as manual signal boxes on the railways — where direct linkages limited the distances between control point and operator. The advent of electronic links, replacing hydraulic and mechanical ones, revolutionised the entire topology of controlling systems. The subsequent twin effects of increasing geographic cover, and economies of scale, has raised the stakes for getting control rooms right the first time. The additional use of computers, to support the decision making undertaken by control room operators, adds yet another dimension to the complexities involved in the planning, design and implementation of control rooms. It is now clear that for most control rooms, and certainly the larger ones, a systematic approach needs to be adopted if the risks of failure are to be avoided. This paper discusses some of the key issues in control room planning and design including an approach based around the International Standard 11064 — The Ergonomic Design of Control Rooms (Ref. 1)

A Smart Actuator for Fault-Tolerant Control

Recent advances in smart actuator and fieldbus technologies are promoting changes in fault-tolerant control design issues. In this paper, a smart actuator scheme is implemented based on a low-cost stepper-motor and CAN bus interface. In order to enhance fault-tolerance capability of the control system, the proposed scheme is focused on self-diagnosis and self-compensation of undesirable actuator characteristics produced by faults. Experimental results with a distributed architecture demonstrator show that actuator faults can be accommodated successfully without a redundant actuator by using the proposed smart actuator scheme.

PID Control for a Distributed System with a Smart Actuator

Recent advances in smart actuator and fieldbus technologies are promoting changes in PID controller design issues. By employing a built-in microprocessor a smart actuator, in general, is capable of self-validation and compensation. In this paper, online retuning of PID controller for a distributed system that contains a smart actuator is explored. The on-line controller retuning is carried out using a set of validation data generated by a smart actuator. The proposed approach is investigated by means of a distributed architecture demonstrator which consists of a set of PCs and a stepper-motor based smart actuator interconnected through fieldbus network.

Controller design issues in the feedback control of radio frequency plasma processing reactors

Feedback control has the potential for improving the reliability and performance of radio frequency (rf) plasma processing reactors for microelectronics etching, deposition, and cleaning applications. Implementation of real-time-control strategies has been slowed by lack of analytic or computational tools to design or optimize systems. To address this need, the virtual plasma equipment model (VPEM) has recently been developed for investigating issues related to feedback control in rf plasma processing equipment. The VPEM has been employed to investigate feedback control of inductively coupled plasma processing reactors for polysilicon etching and, in this article, results from these studies are used in a discussion of controller design, control strategies, and validation of the VPEM. It is demonstrated that response surface based controllers best operate in combination with corrections from an unstructured controller such as a proportional-integral derivative, which relaxes the inherent rigidity of the model-based controller. Since the behavior of plasma processing reactors generally changes over time due to, for example, coatings of the walls, it was found advantageous to make the controllers adaptive.

Design of a controller for a highly coupled V/STOL aircraft

This paper describes the design of a controller for a vertical/shart take-off and landing (V/STOL) aircraft using the Robust Inverse Dynamic Estimation (RIDE) control theory to improve aircraft performance and reduce pilot workload throughout the transition phase from jet to wing-borne flight and vice versa. The controller is required to be effective throughout the speed envelope from hover to 200 knots, during which the aircrafi undergoes significant changes in its dynamics characteristics. The design of the controller is based on a mathematical model of the aircraft linearised at 120 knots, is developed using realistic actuator and sensor models and is extended across the speed range, resulting in the transition envelope controller which is capable of providing acceptable pilot workloads and handling qualities throughout the transition phase. Controller design issues such as the choice of feedback variables, the selection of pilot inceptor configurations and functionalities, and the use of integrator anti-windup techniques in the presence of actuator saturation are discussed. Pilot-in-the-loop simulation studies show that the controller provides good control and handling qualities throughout the transition phase.

Active Reduction of Radiated Noise From a Baffled Piston Using a Volume Velocity, Feedforward Controller

A new active noise-control technique has been developed for control of low-frequency sound generated by vibrating surfaces which is based on minimizing the volume velocity. Noise reduction is achieved by distributing an array of control devices over the surface of the radiating structure. Each device consists of a motion-sensing mechanism, an analog control circuit, and a loudspeaker. The loudspeaker is driven such that it reduces the volume velocity of the radiating structure within its close proximity. This paper briefly presents the theory behind this approach as well as controller design issues. Finally, a discussion of the experimental verification of this concept using a 10-in. uniformly vibrating circular plate (i.e., a baffled piston) and a single noise-control device is given. Broadband (50–500 Hz) sound reductions in the range of 10–20 dB were achieved over a wide spatial area.

Identification, uncertainty characterization and robust control synthesis applied to large flexible structures control

This paper demonstrates an approach to frequency domain identification for the explicit purpose of designing robust H∞ controllers. The approach transforms raw experimental data into a plant set estimate directly usable by modern robust control design software (e.g., Matlab Robust Control Toolboxes). A key issue in control design from raw data is the question of whether the controller will work when applied to the true system. The main feature of this approach is that the resulting controller is guaranteed to work as designed (when applied to the true system) to a prescribed statistical confidence. While the overall methodology addresses key theoretical issues, it has at the same time been specifically designed to support practical implementations. A simulation example is included to demonstrate the overall approach. © 1998 John Wiley & Sons, Ltd.

Identification, uncertainty characterization and robust control synthesis applied to large flexible structures control

This paper demonstrates an approach to frequency domain identification for the explicit purpose of designing robust H(infinity) controllers. The approach transforms raw experimental data into a plant set estimate directly usable by modern robust control design software(e.g., Matlab Robust Control Toolboxes [11][2]). A key issue in control design from raw data is the question of whether the controller will work when applied to the true system. The main feature fo this approach is that the resulting controller in guaranteed to work as designed(when applied to the true system) to a prescribed statistical confidence. While the overall methodology addresses key theoretical issues, it has at the same time been specifically designed to support practical implementations. A simulation example is included to demonstrate the overall approach.

Coupling Between the Modeling and Controller-Design Problems—Part I: Analysis

Controller-design issues influence modeling decisions; therefore, the modeling and controller-design problems are coupled. Part I of this paper proposes a quantification of this coupling in terms of the size of the set of models from which satisfactory controllers may be derived. Moreover, in the context of an extremely general framework, we prove that the coupling increases as performance specifications are tightened and as uncertainty is increased. Furthermore, the existence of a preferred model for controller design is demonstrated; this model is preferred in the sense that its use leads to improved robustness or performance. However, this model does not necessarily satisfy our intuitive notion of a worst-case model; rather, it depends on the performance specifications and uncertainty. The analysis of coupling presented herein motivates the design approach formulated in the companion paper, Part II.

Error control schemes for networks: an overview

In this paper, we investigate the issue of error control in wireless communication networks. We review the alternative error control schemes available for providing reliable end-to-end communication in wireless environments. Through case studies, the performance and tradeoffs of these schemes are shown. Based on the application environments and QoS requirements, the design issues of error control are discussed to achieve the best solution.

Review of high-performance three-phase power-factor correction circuits

This paper reviews progress in topology, control, and design aspects in three-phase power-factor correction (PFC) techniques. Different switching rectifier topologies are presented for various applications. Representative soft-switching schemes, including zero-voltage and zero-current switched pulsewidth modulated (PWM) techniques, are investigated. Merits and limitations of these techniques are discussed and illustrated by experimental results obtained on prototype converters. Control and input filter design issues are also discussed.