There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A current survey of the emerging field of networked control systems is provided. The aim is to introduce the fundamental issues involved in designing successful networked control systems, to provide a snapshot assessment of the current state of research in the field, to suggest useful future research directions, and to provide a broad perspective on recent fundamental results. Reflecting the goals of the Special Issue itself, this paper surveys relevant work from the areas of systems and control, signal processing, detection and estimation, data fusion, and distributed systems. We discuss appropriate network architectures, topics such as coding for robustly stable control in the presence of time-varying channel capacity, channels with fixed versus adaptively variable data width, issues in data rate problems in nonlinear feedback problems, and problems in routing for stability and performance. In surveying current research on networked control systems, we find that recent theoretical advances and target applications are intimately intertwined. The common goal of papers in the Special Issue which follows is to describe key aspects of this relationship. We also aim to provide a bridge between networked control systems and closely related contemporary work dealing with sensor networks and wireless communication protocols

Control and Communication Challenges in Networked Real-Time Systems

The anti-windup technique which can be used to tackle the problems of stability and performance degradation for linear systems with saturated inputs is dealt with. The anti-windup techniques which can be found in the literature today have evolved from many sources and, even now, are diverse and somewhat disconnected from one another. In this survey, an overview of many recent anti-windup techniques is provided and their connections with each other are stated. The anti-windup technique is also explained within the context of its historical emergence and the likely future directions of the field are speculated. The focus is on so-called ‘modern’ anti-windup techniques which began to emerge during the end of the 20th century and which allow a priori guarantees on stability to be made. The survey attempts to provide constructive LMI conditions for the synthesis of anti-windup compensators in both global and local contexts. Finally, some interesting extensions and open problems are discussed, such as nested saturations, the presence of time delays in the state or the input, and anti-windup for non-linear systems.

/pdf/anti-windup-design-an-overview-of-some-recent-advances-and-3c6opbb7h1.pdf

Anti-windup design: an overview of some recent advances and open problems

http://foresight.ifmo.ru/ict/shared/files/201311/1_123.pdf

Decentralized control: An overview

This monograph explores the modeling of conservation and balance laws of one-dimensional hyperbolic systems using partial differential equations. It presents typical examples of hyperbolic systems for a wide range of physical engineering applications, allowing readers to understand the concepts in whichever setting is most familiar to them. With these examples, it also illustrates how control boundary conditions may be defined for the most commonly used control devices.
The authors begin with the simple case of systems of two linear conservation laws and then consider the stability of systems under more general boundary conditions that may be differential, nonlinear, or switching. They then extend their discussion to the case of nonlinear conservation laws and demonstrate the use of Lyapunov functions in this type of analysis. Systems of balance laws are considered next, starting with the linear variety before they move on to more general cases of nonlinear ones. They go on to show how the problem of boundary stabilization of systems of two balance laws by both full-state and dynamic output feedback in observer-controller form is solved by using a “backstepping” method, in which the gains of the feedback laws are solutions of an associated system of linear hyperbolic PDEs. The final chapter presents a case study on the control of navigable rivers to emphasize the main technological features that may occur in real live applications of boundary feedback control.
Stability and Boundary Stabilization of 1-D Hyperbolic Systems will be of interest to graduate students and researchers in applied mathematics and control engineering. The wide range of applications it discusses will help it to have as broad an appeal within these groups as possible.

Stability and Boundary Stabilization of 1-D Hyperbolic Systems

Irrigation networks of open-water channels are used throughout the world to support agricultural activity. By and large, these networks are managed in open loop. To achieve closed-loop water distribution management, it is necessary to augment these civil engineering systems with an appropriate information infrastructure-sensors, actuators, information processing, and communication resources. Recent pilot projects in Australia demonstrate the significant potential of closed-loop management, which can yield a significant improvement in the quality of service, while achieving improved water distribution efficiency. This paper focuses on the modelling and closed-loop control of open-water channels from the perspective of large-scale irrigation network management. Several feedback information structures are discussed and the key design tradeoffs identified

Control of Large-Scale Irrigation Networks

http://www.nt.ntnu.no/users/skoge/prost/proceedings/ifac2005/Fullpapers/05174.pdf

Systems engineering for irrigation systems: Successes and challenges

Extremum seeking control (ESC) is an adaptive control scheme that locates an extremum of an input-output map, without any explicit knowledge of this map apart from its existence. As is typical in adaptive control an integrator is used to drive the parameters that are being adapted. Due to this integrator, it is possible that the adapted parameters wander outside their physically relevant domain as the underlying adaptation technique is blind to this constraint. As these constraints may represent realistic operational limits it is important to design ESC to respect them. Two such ESC schemes are proposed. One is based on a constrained optimization approach in which some penalty function is used to adapt the search so as not to violate the constraints. The other technique uses an anti-windup scheme, a widely used mechanism in engineering to prevent windup of integral action in a controller. It is demonstrated that both methods are essentially equivalent. In that for any penalty-function based ESC, there exists an equivalent anti-windup ESC whose phase portrait is a global approximate of the penalty-function ESC. Some simulations are presented to illustrate the main results.

Extremum Seeking for Constrained Inputs

We consider the propagation of water-level errors in a controlled string of (identical) pools comprising an open-water irrigation channel. It is shown that water-level errors are amplified as they propagate upstream, whenever the feedback control scheme is decentralised and load-disturbance rejection is required in steady-state. Moreover, a design trade-off is identified between local performance, in terms of set-point regulation and load-disturbance rejection, and the error-propagation characteristics. The use of feed-forward/decoupling paths is considered in terms of managing this trade-off. However, the corresponding analysis suggests it is difficult to exploit the extra degree of freedom. Finally, we investigate a so-called distributed generalisation of the decentralised schemes. This leads to an optimal control based framework for dealing with the design trade-off.

/pdf/on-water-level-error-propagation-in-controlled-irrigation-53v6xgjf3h.pdf

Yuping Li

Papers

Control of Large-Scale Irrigation Networks

Systems engineering for irrigation systems: Successes and challenges

Extremum Seeking for Constrained Inputs

On Water-Level Error Propagation in Controlled Irrigation Channels

Anti-windup for marginally stable plants and its application to open water channel control systems