Optimal communication logics in networked control systems (original) (raw)

Optimal controller design for networked control systems

… of the 17th IFAC world congress, 2008

This paper addresses the problem of optimal control system design for networked control systems. We focus on a situation where the plant is single-input single-output and the communication link between the controller and the plant is signal-to-noise ratio constrained. In this setting, we characterize the controllers that minimize the tracking error variance, while respecting the channel signal-to-noise ratio constraint. We also provide a description of the optimal tradeoff curve in the performance versus signal-to-noise ratio plane and, as a byproduct, we establish easily computable bounds on the achievable performance. We illustrate our results with a numerical example based on a bit rate limited channel.

A Survey of Recent Results in Networked Control Systems

Proceedings of The IEEE, 2007

Networked Control Systems (NCSs) are spatially distributed systems for which the communication between sensors, actuators, and controllers is supported by a shared communication network. In this paper we review several recent results on estimation, analysis, and controller synthesis for NCSs. The results surveyed address channel limitations in terms of packet-rates, sampling, network delay and packet dropouts. The results are presented in a tutorial fashion, comparing alternative methodologies.

Fundamental Issues in Networked Control Systems

This paper provides a survey on modeling and theories of networked control systems (NCS). In the first part, modeling of the different types of imperfections that affect NCS is discussed. These imperfections are quantization errors, packet dropouts, variable sampling/transmission intervals, variable transmission delays, and communication constraints. Then follows in the second part a presentation of several theories that have been applied for controlling networked systems. These theories include: input delay system approach, Markovian system approach, switched system approach, stochastic system approach, impulsive system approach, and predictive control approach. In the last part, some advanced issues in NCS including decentralized and distributed NCS, cloud control system, and co-design of NCS are reviewed.

Communication logics for networked control systems

2004

This paper addresses the control of spatially distributed processes. We utilize a distributed architecture in which multiple local controllers coordinate their efforts through a data network that allows information exchange. We focus our work on linear time invariant processes disturbed by Gaussian white noise and propose several logics to determine when the local controllers should communicate. We provide conditions under which these logics guarantee boundedness and investigate the trade-off between the amount of information exchanged and the performance achieved. The resulting closed-loop systems evolve according to stochastic differential equations with resets triggered by stochastic counters. This type of stochastic hybrid system seems to be interesting on its own. The theoretical results are validated through Monte Carlo simulations.

Networked control systems with packet delays and losses

Conference on Decision and Control, 2008

We investigate the effect of packet delays and packet drops on networked control systems. First we consider the problem of where to locate a controller or state estimator in a network, and show that under a Long Packets Assumption (LPA) it is optimal to collocate it with the actuator. We then show that under the LPA, stabilizability is only determined

Minimizing down-link traffic in networked control systems via optimal control techniques

Decision and Control, …, 2003

This paper presents a control strategy for multivariable plants where controller and actuators are connected via a digital data-rate limited channel. In order to minimize bandwidth utilization, a communication constraint is imposed, which restricts all data transmitted to belong to a finite set and only permits one plant input to be addressed at a time. We develop a new scheme, which aims at optimizing quadratic performance under the above communication constraint. A key aspect of this contribution is the implementation of the control scheme to a real laboratory-scale system.

Suboptimal Guaranteed Cost Controller Design for Networked Control Systems

2006

This paper is concerned with the guaranteed cost controller design of networked control systems. The continuous time plant with state-delay is studied. A new model of the networked control systems is proposed under consideration of the network-induced delay and data packet dropout. In terms of the given model, a suboptimal guaranteed cost controller design method is proposed based on linear matrix inequalities (LMI) approach. Suboptimal Allowable Equivalent Delay Bound (SAEDB) and the feedback gain of a memoryless controller can be derived by solving a set of LMI for the networked control system based on Lyapunov functional method. An example is given to show the effectiveness of our method.

On the modeling of networked controlled systems

2007 Mediterranean Conference on Control and Automation, MED, 2007

In this article 1 modeling approaches for Networked Controlled Systems (NCS) with different types of varying communication latency times are presented. The embedded delays are unknown, bounded and depending on their size relative to the sampling period, four different models are offered. There is distinct treatment for delays longer than one sampling period, since these are decomposed to a term which is integer multiple of the sampling period and a residual which can be time-varying. The careful mixing of asynchronous (event-driven) and synchronized (sampled) signals can lead to discrete time uncertain and possibly switched systems, where classical control approaches could be applied.

Optimal Integrated Control and Scheduling of Systems with Communication Constraints

Proceedings of the 44th IEEE Conference on Decision and Control

This paper addresses the problem of the optimal control and scheduling of Networked Control Systems over limited bandwidth time-slotted networks. Multivariable linear systems subject to communication constraints are modeled in the Mixed Logical Dynamical (MLD) framework. The translation of the MLD model into the Mixed Integer Quadratic Programming (MIQP) formulation is described. This formulation allows the solving of the optimal control and scheduling problem using efficient branch and bound algorithms. Advantages and drawbacks of on-line and off-line scheduling algorithms are discussed. Based on this discussion, an efficient on-line scheduling algorithm, which can be seen as a compromise, is presented and its performance is evaluated. I. INTRODUCTION Shared communication networks are increasingly being used to support the information exchange in distributed control systems. Using a control network has many advantages, such as a higher reliability, an easier deployment and maintenance. However, many communication networks are subject to bandwidth constraints (for example Underwater Acoustic Networks [1] or Wireless Networks [2]). Reasons behind these resource constraints are multiple. Guaranteeing deterministic real-time communications induces important restrictions on the available bandwidth, especially when the communication channel is noisy. In other situations, some nodes of the communication network may be autonomous and battery-powered. The lifetime of the batteries limits the energy used in the transmission and thus limits the bandwidth of the communications. On the other hand, in the automotive industry, an increasing number of applications are being developed in order to improve the driving safety and comfort. These applications need to share and to exchange an important amount of information. As a consequence, the local bus is becoming more and more loaded. Using a more expensive technology can solve these problems, but components price is strongly balanced by production cost requirements. Many research works addressed the problems stemming from the use of communication networks in control loops from different points of view, see for example [3]-[6]. Recently, it was shown that considering jointly control and real-time scheduling leads to an improvement of the control performance [7], [8]. In [9], the problem of the optimal off-line control and scheduling over TDMA networks is MM. Ben Gaid and A. Ç ela are with the COSI Lab., ESIEE,

Distributed Bandwidth Management in Networked Control Systems

Bandwidth allocation techniques for control loops closed over communication networks are based on static strategies that ensure average control performance at the expense of permanently occupying the available bandwidth. We present a dynamic approach to bandwidth management in networked control systems that allows control loops to consume bandwidth according to the dynamics of the controlled process while attempting to optimize overall control performance. By augmenting the original state-space representation of each controlled process with a new state variable that describes the network dynamics, 1) the allocation of bandwidth to control loops can be done locally at run-time according to the state of each controlled process without causing overload situations and 2) control laws can be designed to account for the variations in the assigned bandwidth preventing the unexpected control performance degradation and even destabilization that would otherwise occur. Experimental data shows that this approach improves control performance with respect to the static strategy and uses less bandwidth.