A “Globally” Convergent Controller for Multi-Machine Power Systems Using Structure-Preserving Models

The design of excitation controllers to improve transient stabilization of power systems is a topic of renewed interest in the control community. Existence of a state-feedback stabilizing law for multi-machine aggregated reduced network models has recently been established. In this paper we extend this result in two directions: first, in contrast with aggregated models, we consider the more natural and widely popular structure-preserving models that preserve the identity of the network components (generators, loads and lines) and allow for a more realistic treatment of the loads. Second, we explicitly compute a control law that, under a detectability assumption, ensures that all trajectories converge to the desired equilibrium point, provided that they start and remain in the region where the model makes physical sense.     

“Beating” Fitts’ law: virtual enhancements for pointing facilitation

We survey recent research into new techniques for artificially facilitating pointing at targets in graphical user interfaces. While pointing in the physical world is governed by Fitts’ law and constrained by physical laws, pointing in the virtual world does not necessarily have to abide by the same constraints, opening the possibility for “beating” Fitts’ law with the aid of the computer by artificially reducing the target distance, increasing the target width, or both. The survey suggests that while the techniques developed to date are promising, particularly when applied to the selection of single isolated targets, many of them do not scale well to the common situation in graphical user interfaces where multiple targets are located in close proximity.     

“Paraprogramming” manufacturing information systems

Computer integrated manufacturing (CIM) is creating unexpected problems for a growing number of manufacturing companies. Manufacturers are finding it especially difficult to attract programmers who are both willing and able to develop the highly complex software that integrates existing accounting, sales, production, engineering, and quality control information subsystems. Consequently, many companies abdicate their responsibility for manufacturing information systems and seek third party support ranging from consulting assistance to a total takeover of the company's information resources and operations. Companies that “give away” their internal information system capabilities to third parties will ultimately lose control of their enterprise information, a danger to be avoided. Off-the-shelf software for desktop computers has become sufficiently powerful to help solve a major portion of this serious problem. We hypothesize that manufacturing engineers (and others) can be trained to use packaged software to leverage their company's systems programming capabilities. In effect they would become “paraprogrammers” who would help design, develop, and maintain manufacturing information systems. This new type of professional would not require a computer science or similar educational background, but could be trained to satisfy many specialized programming needs in a manner similar to how paramedics and paralegals are trained and used in the medical and legal professions, respectively. This paper reports on the early stages of research to determine whether or not product design engineers can use a desktop relational database management system and its various command languages to develop a master bill of material information system (BOMIS). The purpose of the research is to evaluate the amount of programming complexity reduction and increased operational effectiveness that can be achieved through paraprogramming by manufacturing engineers.     

Improved closed‐loop stability for fixed‐point controller realizations using the delta operator

A stable discrete‐time control system may achieve a lower than predicted performance or even become unstable when the discrete‐time control law is implemented with a fixed‐point digital control processor due to the finite word length (FWL) effects, which depends on the control law state‐space realization and the discrete‐time operator (e.g., the delta operator or the forward‐shift operator) used to represent the control law. To improve the closed‐loop stability (and as a byproduct, performance) when the control law is implemented, a state‐space approach that selects the control law realization to optimize a stability‐related objective function is developed using the delta operator. Analytical and numerical comparison of the fixed‐point performance of delta control laws with the performance of the corresponding forward‐shift control laws quantifies the improved closed‐loop stability of the delta realizations over those of the corresponding forward‐shift realizations. It is also shown that there exists a simple mapping between the optimal FWL forward‐shift control law realizations and the optimal FWL delta control law realizations. The results are illustrated by delta and forward‐shift control law realizations of a discrete‐time H_∞ control law designed for a teleoperation motion‐scaling system. Copyright © 2001 John Wiley & Sons, Ltd.     

Digital News Consumption and Copyright Intervention: Evidence from Spain Before and After the 2015 “Link Tax”

We analyze patterns of digital news consumption before and after a “link tax” was introduced in Spain. This new legislation imposed a copyright fee for showing snippets of content created by newspapers and resulted in the shutdown of Google News Spain. The Spanish copyright law is a precedent to the Copyright Directive currently submitted to the European Parliament, which is planning to impose a similar “link tax.” We offer empirical evidence that can help evaluate the impact of that sort of intervention. We analyze data tracking news consumption behavior to assess changes in audience reach and audience fragmentation. We show that the law has no discernible impact on reach, but we identify an increase in the fragmentation of news consumption.     

Robot control system using “intelligent” integrators

Integral control is important in practice, but in many applications for robot systems this control is unsatisfactory, due to large initial conditions or disturbances. The overshoot becomes large, the speed of response not fast enough, and path tracking is needed. One cure for this problem is the use of the intelligent integral controller, which is very simple in implementation. This control scheme, as part of a PID controller, is applied to a robot system and its superiority, from the conventional one, becomes clear. The main advantage of this controller is that it gives very satisfactory results, while being rather simple.     

Comments on “Scalable Services via Egress Admission Control”

In the recent paper by Cetinkaya et al , admission control tests are derived by approximating the sum of two Gumbel distributed random variables by a Gumbel distributed random variable. In fact, the sum of two Gumbel distributed random variables does not follow a Gumbel distribution. Here, explicit expressions are derived for the probability density function (pdf) and the cumulative distribution function (cdf) of the exact distribution of the sum. The discrepancy between the exact and the approximate distributions is studied numerically.     

Modelling rhetorical legal “logic”—a double syllogism

This paper looks at legal reasoning from the point of view of the work of the lawyer, rather than the law itself. In the case of Common Law systems, this means a more flexible view of how tasks are divided between the humans and the computer system, with an emphasis on decision support rather than complete automation. A process-based model of the lawyer's work is proposed in the form of a double syllogism, which displays an aesthetically pleasing symmetry, but also a significant asymmetry in the role played by perceived precedents. This arises from the use of inductive, rather than deductive, reasoning. The potential complications arising from the issue of the perception of precedents are discussed in depth.The double-syllogism model is then considered in the light of CommonKADS terminology and models. It is suggested that decision support systems using knowledge-based techniques, as required to support lawyers working under Common Law jurisdiction, raise a stronger form of the interaction problem that is well known in knowledge-based systems. This means that such systems are not well catered for in the existing CommonKADS Organisational, Agent, Task and Communication Models. The double-syllogism model is suggested as a supplement to CommonKADS in the development of such systems, at least until a more generic addition is available.     

Robust variable structure and switching-Σ adaptive control ofsingle-arm dynamics

In this paper, the variable structure control (VSC) and switching-σ adaptive laws are used to design a new robust controller for single-arm rigid manipulators in joint space. The controller is shown to be robust with respect to bounded disturbance. More particularly, a bound on the tracking error is determined and shown to be smaller than those resulting from the VSC) law proposed in Slotine and Li as well as the robust adaptive control law derived in Reed and Ioannou. The simulations also show that the proposed control law has better tracking precision performance than the VSC law and switching-σ adaptive control law. It can also suppress chattering and maintain good tracking precision even if actuator unmodeled dynamics are considered     

Singularity‐avoiding swing‐up control for underactuated three‐link gymnast robot using virtual coupling between control torques

An underactuated three‐link gymnast robot (UTGR) is a simple model of a gymnast on a high bar. The control objective of a UTGR is to swing it up from a point near the straight‐down position and to stabilize it at the straight‐up position. To achieve this, we first divide the motion space into two subspaces, swing‐up area and balancing area, and design a controller for each. The design of a swing‐up control law that ensures that the UTGR enters the balancing area is crucial because the UTGR is subject to a nonholonomic constraint and is highly nonlinear during the swing‐up motion. This study focused on how to design a swing‐up control law that contains no singularities. The key concept is the introduction of a virtual coupling between control torques, which converts the problem of avoiding singularities to one of imposing constraints on the parameters of the control law and properly selecting those parameters. A swing‐up control law thus designed ensures that the UTGR enters the balancing area in a natural stretched‐out posture. This makes it easy to stabilize the UTGR in the balancing area. Copyright © 2013 John Wiley & Sons, Ltd.     

MCLP-based methods for improving “Bad” catching rate in credit cardholder behavior analysis

Cardholders’ behavior prediction is an important issue in credit card portfolio management. As a promising data mining approach, multiple criteria programming (MCLP) has been successfully applied to classify credit cardholders’ behavior into two groups. In order to better control credit risk for financial institutes, this paper proposes three methods based on MCLP to improve the “Bad” catching accuracy rate. One is called MCLP with unbalanced training set selection, the second is called fuzzy linear programming (FLP) method with moving boundary, and the third is called penalized multi criteria linear programming (PMCLP). The experimental examples demonstrate the promising performance of these methods.     

Design of non‐fragile guaranteed‐cost repetitive‐control system based on two‐dimensional model

This paper concerns a new method of repetitive control based on two‐dimensional (2D) system theory. First, a 2D model is presented that enables the independent adjustment of control, which happens within a repetition period, and learning, which happens between periods. Next, the problem of designing a repetitive‐control law is formulated as a state‐feedback design problem for the 2D model. An existence condition and a method of designing a robust repetitive‐control law for a plant containing time‐invariant structured uncertainties are established by combining 2D system theory with linear matrix inequalities. Then, based on those results, a non‐fragile guaranteed‐cost repetitive‐control law is derived. The controller gain to be designed is assumed to have additive gain variations. It guarantees that the value of a quadratic performance function is less than a specified upper bound for all admissible uncertainties. The main feature of this approach is that it enables the control action and the learning process to be adjusted independently by the direct tuning of the weighting matrices in the quadratic cost function. Finally, a numerical example demonstrates the validity of this approach. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

A time differences of arrival‐based homing strategy for autonomous underwater vehicles

A new sensor‐based homing integrated guidance and control law is presented to drive an underactuated autonomous underwater vehicle (AUV) toward a fixed target, in 3‐D, using the information provided by an ultra‐short baseline (USBL) positioning system. The guidance and control law is first derived at a kinematic level, expressed on the space of the time differences of arrival (TDOAs), as directly measured by the USBL sensor, and assuming the plane wave approximation. Afterwards, the control law is extended for the dynamics of an underactuated AUV resorting to backstepping techniques. The proposed Lyapunov‐based control law yields almost global asymptotic stability (AGAS) in the absence of external disturbances and is further extended, keeping the same properties, to the case where known ocean currents affect the motion of the vehicle. Simulations are presented and discussed that illustrate the performance and behavior of the overall closed‐loop system in the presence of realistic sensor measurements and actuator saturation. Copyright © 2009 John Wiley & Sons, Ltd.     

Passivity‐based control for large‐signal stability of high‐order switching converters

This article presents a new passivity‐based control law that stabilizes the output voltage of a high‐order DC‐DC converter. Such nonlinear control law assures robust large‐signal stability, provides zero steady‐state error despite uncertainty in converter parameters and has enough degree of freedom to satisfy the usual transient specifications of DC‐DC converters. This new integral control is derived in three steps. First, a static law is obtained. Second, a positive semidefinite storage function is synthesized to guarantee zero steady‐state error of the output voltage. Finally, the storage functions of the first two steps are combined to derive the new control law for high‐order DC‐DC converters. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Model predictive tracking control for a linear system under time‐varying input constraints

In this paper, we propose a tracking control law for a linear dynamical system under time‐varying input constraints. The proposed control law consists of a dual‐mode model predictive control (MPC) law and a target recalculation mechanism. As the terminal controller of the dual‐mode MPC, we propose a saturation‐level‐dependent gain‐scheduled feedback control law that ensures closed‐loop stability against arbitrary change of the position limit of the actuators. We also present conditions that guarantee feasibility and stability of the control algorithm under time‐varying input constraints. The control algorithm is reduced to an online optimization problem under linear matrix inequality constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

Visualizing “typical” and “exotic” Internet traffic data

The threat of cyber attacks motivates the need to monitor Internet traffic data for potentially abnormal behavior. Due to the enormous volumes of such data, statistical process monitoring tools, such as those traditionally used on data in the product manufacturing arena, are inadequate. “Exotic” data may indicate a potential attack; detecting such data requires a characterization of “typical” data. We devise some new graphical displays, including a “skyline plot,” that permit ready visual identification of unusual Internet traffic patterns in “streaming” data, and use appropriate statistical measures to help identify potential cyberattacks. These methods are illustrated on a moderate-sized data set (135,605 records) collected at George Mason University.     

Bearing‐only control of directed cycle formations: Almost global convergence and hardware implementation

In this article, we study bearing‐only control of directed cyclic formations. First, we provide a necessary and sufficient condition on the bearing constraints so that the directed cycle formation of n‐agents in (n?1)‐dimensional space is infinitesimally bearing rigid. Second, a bearing‐only control law which only allows motions perpendicular to the desired bearing vector is proposed. Under this control law, the agents globally asymptotically converge to a desired formation which is fully determined from their initial positions and desired bearing vectors. Finally, the proposed formation control law is implemented on mobile robots to support the analysis.     

Non-linear mechanic and electric behavior of a robot axis with a “harmonic-drive” gear

This paper presents a study of a complete robot axis including the electrical and the mechanical parts. The motorization of the robot arm presented here has been carried out using a DC motor, a “harmonic-drive” type gear system and three control loops (current, speed and position). Each component is studied and modeled taking into account non-linearities such as current limitation, backlash, low rigidity and non-linear friction. The results obtained through computation of the model are compared with measurements on the real arm (motor current and speed) using speed and position loops.     

A Practical Iterative Learning Path‐Following Control Of An Omni‐Directional Vehicle

A new practical iterative learning control (ILC) updating law is proposed to improve the path following accuracy for an omni‐directional autonomous mobile robot. The ILC scheme is applied as a feedforward controller to the existing feedback controller. By using the local symmetrical double‐integral of the feedback control signal of the previous iteration, the ILC updating law takes a simple form with only two design parameters: the learning gain and the range of local integration. Convergence analysis is presented together with a design procedure. Simulation results on a difficult maneuver are presented to illustrate the effectiveness of the proposed simple and yet practical scheme. The simulation is based on the model of a novel robotic platform, the Utah State University (USU) Omni‐Directional Vehicle (ODV), which uses multiple “smart wheels,” whose speed and direction can be independently controlled through dedicated processors for each wheel.     

Output‐based disturbance rejection control for 1‐D anti‐stable Schrödinger equation with boundary input matched unknown disturbance

In this paper, we are concerned with the output feedback control design for a system (plant) described by a boundary controlled anti‐stable one‐dimensional Schrödinger equation. Our output measure signals are the displacements at both side. An untraditional infinite‐dimensional disturbance estimator is developed to estimate the disturbance. Based on the estimator, we propose a state observer that is exponentially convergent to the original system and then design a stabilizing control law consisting of two parts: The first part is to compensate the disturbance by using its approximated value and the second part is to stabilize the observer system by applying the classical backstepping approach. The resulting closed‐loop system is shown to be exponentially stable with guaranteeing that all internal systems are uniformly bounded. An effective output‐based disturbance rejection control algorithm is concluded. An application, namely, a cascade of ODE–wave systems, is investigated by the developed control algorithm. Numerical experiments are carried out to illustrate the effectiveness of the proposed control law. Copyright © 2017 John Wiley & Sons, Ltd.