Performance Of Networked Control Systems Research Articles

A Switched System Approach to Exponential Stabilization Through Communication Network

This paper considers a networked control loop, where the plant is a “slave” part, and the remote controller and observer constitute the “master”. Since the performance of networked control systems (NCS) depends on the quality of service (QoS) available from the network, it is worth to design a controller that takes into account qualitative information on the QoS in realtime. The goal of the design is to provide a controller that guarantees the following two things: 1) high performances (here expressed by exponential decay rates) when the QoS remains globally the same and 2) global stability when the QoS changes. In order to guarantee the global stability, the controller will switch by respecting a dwell time constraint. The dwell time parameters are obtained by using the switched system theories and the obtained conditions are linear matrix inequalities. An experiment illustrates how the controller can be implemented for a control over Internet application (remote control of a small robot).

Finite-time Stabilization of Networked Control Systems Subject to Communication Delay

This paper investigates the finite-time control problem for networked control systems (NCSs) with network-induced delay. A particular linear transformation is introduced to convert the original time- delay system into a delay-free form. Based on finite-time stability theory combined with linear matrix inequalities (LMIs) techniques, a sufficient condition that ensures finite-time performance of networked control systems is derived. Numerical example illustrates the feasibility of the developed approaches.

Research on the Rate Control Scheme of Networked Control Systems

The Quality of performance of Networked control system (NCS) depends on the quality of network service. To guarantee the limit of quality of network service of NCS, the mechanism of end-to-end rate control is applied to NCS. An novel end-to-end rate control scheme of guaranteeing minimal rate for each control loop of NCS is proposed. This scheme can guarantee to meet the requirements of quality of network service of NCS and show TCP friendly. Finally, the simulation results show that the proposed algorithm is effective.

Smith Predictor Based on Predicting Induced-Delay

Since communication network is introduced into control system, induced-delay appears. Because of the delay, the performance of networked control system becomes bad, even unsteady. Conventional Smith predictor is sensitive to error in object model and needs delay’s value in advance. Regarding random delay, its application is limited. In this paper, we propose a method based on induced-delay predicted by BP neural network, which use two historical delay values to predict the next one. Smith predictor adjusts its parameters according to that value in time. The simulating results indicate that the precision of delay-predicting can be ensured and the performance of networked control system has been improved.

Study of Predictive Control in Industrial Networked Control System

In order to improve the performance of networked control system which has the characteristic of uncertain time delay, predictive control is adopted. The model of networked control system is analyzed. Take into account uncertain network time delay caused by various factors and problem of model mismatch, predictive controller is designed and simulation model of system is built using software of Matlab. A method of reducing model mismatch is proposed. Study results show that predictive control can make networked control system with good performance.

Fractional Gain Scheduled Controller for a Networked Smart Wheel: Experimental Results

AbstractThe performance of Networked Control Systems (NCS) is directly affected mainly by time-varying network delays, so a specific approach to compensate their effects is usually required during the controller design process. This paper deals with the control of an experimental platform over the Internet by applying a novel fractional gain scheduling strategy which enables an existing fractional order PI controller for efficient control over the network. The proposed controller introduces delay-adaptive gains, which are optimal with respect to the current network condition. Experimental results show the effectiveness of the proposed controller, providing significantly better system performance, especially when the network-induced delay is increased in certain circumstances.

Stability and Performance of Networked Control Systems with Time-multiplexed Sensors and Oversampled Observer

AbstractIn this paper we analyze the scenario where a set of wireless sensors are time-multiplexed in order to reduce the traffic load and energy consumption in a Networked Control System. The possible choices for scheduling the transmission of measures are explored under the concept of periodic feedback patterns, i.e. repeated sequences of different measures. The length and structure of such patterns are chosen to guarantee stability of the closed loop and to minimize a predefined performance index. The control scheme is enhanced with a controller-side observer running at a rate higher than the sampling rate, for which a novel stability problem is stated and solved.

Main Stream Temperature Control System Based on Smith-PID Scheduling Network Control

This paper is concerned with the controller design problem for a class of networked main stream temperature control system with long random time delay and packet losses. To compensate the effect of time delay and packet losses, a gain-scheduling based Smith-PID controller is proposed for the considered networked control systems (NCSs). Moreover, to further improve the control performance of NCSs, genetic algorithm is employed to obtain the optimal control parameters for gain-scheduling Smith-PID controller. Simulation results are given to demonstrate the effectiveness of the proposed methods.

To Zero or to Hold Control Inputs With Lossy Links?

This technical note studies the linear quadratic (LQ) performance of networked control systems where control packets are subject to loss. In particular we explore the two simplest compensation strategies commonly found in the literature: the zero-input strategy, in which the input to the plant is set to zero if a packet is dropped, and the hold-input strategy, in which the previous control input is used if packet is lost. We derive expressions for computing the optimal static gain for both strategies and we compare their performance on some numerical examples. Interestingly, none of the two can be claimed superior to the other, even for simple scalar systems, since there are scenarios where one strategy performs better then the other and scenarios where the converse occurs.

To Drop or Not to Drop: Design Principles for Kalman Filtering Over Wireless Fading Channels

It is the general assumption that in estimation and control over wireless links, the receiver should drop any erroneous packets. While this approach is appropriate for non real-time data-network applications, it can result in instability and loss of performance in networked control systems. In this technical note we consider estimation of a multiple-input multiple-output dynamical system over a mobile fading communication channel using a Kalman filter. We show that the communication protocols suitable for other already-existing applications like data networks may not be entirely applicable for estimation and control of a rapidly changing dynamical system. We then develop new design paradigms in terms of handling noisy packets for such delay-sensitive applications. We reformulate the estimation problem to include the impact of stochastic communication noise in the erroneous packets. We prove that, in the absence of a permanent cross-layer information path, packet drop should be designed to balance information loss and communication noise in order to optimize the performance.

A Switched Control Method for Networked Control Systems

Abstract The performance of networked control systems based on a switched control law is studied. The control law is switched between sampled-data feedback and zero control, the switch instant of which is determined by a switching parameter. The objective of this paper is to analyze 1) under what condition the switched control law can lead to better performance than the standard one and 2) how to select the switching parameter if the condition is satisfied. Numerical examples show the effectiveness of the proposed results.

Optimal Performance of Networked Control Systems with Nonclassical Information Structures

A discrete time stochastic feedback control system consisting of a nonlinear plant, a sensor, a controller, and a noisy communication channel between the sensor and the controller is considered. The sensor has limited memory and, at each time, it transmits an encoded symbol over the channel and updates its memory. The controller receives a noise-corrupted copy of the transmitted symbol. It generates a control action based on all its past observations and all its past actions. This control action is fed back to the plant. At each time instant the system incurs an instantaneous cost depending on the state of the plant and the control action. The objective is to choose encoding, memory update, and control strategies to minimize an expected total cost over a finite horizon, or an expected discounted cost over an infinite horizon, or an average cost per unit time over an infinite horizon. A solution methodology for obtaining a sequential decomposition of the global optimization problem is developed. This solution methodology is extended to the case when the sensor makes an imperfect observation of the state of the plant.

Predictive Control for Time-Varying Delay in Networked Control Systems

Network delay is the main factor that deteriorates the performance of Networked Control Systems (NCSs). In order to compensate the effects of the variable time delay induced in a NCS, two new methods based on a Predictive Control Strategy are proposed in this paper. It is assumed that the delays in the communication network are bounded and, either an average value of these delays, or a model that estimates the system including the delays in the communication network is used in order to apply the predictive control algorithm. The performances of the proposed methods are demonstrated by simulation results and corresponding comparisons prove the significance of these methods.

A synthesizing control model of networked control systems to guarantee QoP and QoS

The whole performance of the networked control system (NCSs) depends on two interaction factors, namely the quality of control performance (QoP) and quality of network service (QoS). So, to optimize the whole performance of NCSs, the problem of guaranteeing QoP and QoS plays an important role in the design of NCSs. However, up to now, little work has been done in this field. In this paper, a synthesizing control model of NCSs to guarantee QoP and QoS is proposed, and a feasible condition of optimizing whole performance of NCSs is also suggested. Finally, the simulation results show that the proposed model is effective.

QoS-Based Remote Control of Networked Control Systems Via Profibus Token Passing Protocol

This paper focuses on a quality-of-service (QoS)-based remote control scheme for networked control systems via the Profibus token passing protocol. Typically, token passing experiences random network delay due to uncertainties in token circulation, but the protocol has in-built upper and lower bounds of network delay. Thus, to ensure the control performance of networked control systems via the Profibus token passing protocol, the network delay should be maintained below the allowable delay level. As the network delay is affected by protocol parameters, such as target rotation time, we present here an algorithm for selection of target rotation time using a genetic algorithm to ensure QoS of control information. We also discuss the performance of the QoS-based remote control scheme under conditions of controlled network delay. To evaluate its feasibility, a networked control system for a feedback control system using a servo motor was implemented on a Profibus-FMS network.

Network-based robust [formula omitted] control of systems with uncertainty

This paper is concerned with the design of robust H ∞ controllers for uncertain networked control systems (NCSs) with the effects of both the network-induced delay and data dropout taken into consideration. A new analysis method for H ∞ performance of NCSs is provided by introducing some slack matrix variables and employing the information of the lower bound of the network-induced delay. The designed H ∞ controller is of memoryless type, which can be obtained by solving a set of linear matrix inequalities. Numerical examples and simulation results are given finally to illustrate the effectiveness of the method.

STABILITY RESULTS FOR NETWORKED CONTROL SYSTEMS SUBJECT TO PACKET DROPOUTS

Stability and performance of networked control systems has been a recent area of interest in the control literature. The inclusion of a shared communication network between plant and controller inevitably leads to occasional random data loss. We provide novel results relating to the probability of such a system being globally asymptotically stable or input to state stable.

DESIGN AND IMPLEMENTATION OF NETWORKED PREDICTIVE CONTROL SYSTEMS

This paper discusses the design and implementation of networked predictive control systems. A networked predictive control algorithm is proposed to compensate the network delay and achieve desired control performance of networked control systems. Two schemes of networked control systems are presented: one is the off-line simulation scheme and the other is a real-time application. Based on a networked control system test rig, the networked predictive control algorithm is implemented and applied to a practical servo control system. The simulation and practical experiment results illustrate the efficiency and feasibility of the proposed networked predictive control algorithm and simulation schemes.

Gain Scheduler Middleware: A Methodology to Enable Existing Controllers for Networked Control and Teleoperation—Part I: Networked Control

Conventionally, in order to control an application over a data network, a specific networked control or teleoperation algorithm to compensate network delay effects is usually required for controller design. Therefore, an existing controller has to be redesigned or replaced by a new controller system. This replacement process is usually costly, inconvenient, and time consuming. In this paper, a novel methodology to enable existing controllers for networked control and teleoperation by middleware is introduced. The proposed methodology uses middleware to modify the output of an existing controller based on a gain scheduling algorithm with respect to the current network traffic conditions. Since the existing controller can still be utilized, this approach could save much time and investment cost. Two examples of the middleware applied for networked control and teleoperation with IP network delays are given in these two companion papers. Part I of these two companion papers introduces the concept of the proposed middleware approach. Formulation, delay modeling, and optimal gain finding based on a cost function for a case study on DC motor speed control with a proportional-integral (PI) controller are also described. Simulation results of the PI controller shows that, with the existence of IP network delays, the middleware can effectively maintain the networked control system performance and stabilize the system. Part II of this paper will cover the use of the proposed middleware concept for a mobile robot teleoperation.

Gain Scheduler Middleware: A Methodology to Enable Existing Controllers for Networked Control and Teleoperation—Part II: Teleoperation

Conventionally, in order to control an application over a data network, a specific networked control or teleoperation algorithm to compensate network delay effects is usually required for controller design. Therefore, an existing controller has to be redesigned or replaced by a new controller system. This replacement process is usually costly, inconvenient, and time consuming. In this paper, a novel methodology to enable existing controllers for networked control and teleoperation by middleware is introduced. The proposed methodology uses middleware to modify the output of an existing controller based on a gain scheduling algorithm with respect to the current network traffic conditions. Since the existing controller can still be utilized, this approach could save much time and investment cost. Two examples of the middleware applied for networked control and teleoperation with IP network delays are given in these two companion papers. Part I of these two companion papers introduces the concept of the proposed middleware approach. Formulation, delay modeling, and optimal gain finding based on a cost function for a case study on DC motor speed control with a proportional-integral (PI) controller are also described. Simulation results of the PI controller shows that, with the existence of IP network delays, the middleware can effectively maintain the networked control system performance and stabilize the system. Part II of this paper will cover the use of the proposed middleware concept for a mobile robot teleoperation.