Redundant data transmission in control/estimation over lossy networks

Connecting a complex control system with various sensors, actuators, and controllers as a networked control system by a shared data network can effectively reduce complicated wiring connections. This system is also easy to install and maintain. The trend is to use networked control systems for time-sensitive applications, such as remote DC motor actuation control. The performance of a networked control system can be improved if the network can guarantee quality-of-service (QoS). Due to time-varying network traffic demands and disturbances, QoS requirements provided by a network may change. In this case, a network has to reallocate its resources and may not be able to provide QoS requirements to a networked control application as needed. Therefore, the application may have to gracefully degrade its performance and perform the task as best as possible with the provided network QoS. This paper proposes a novel approach for networked DC motor control systems using controller gain adaptation to compensate for the changes in QoS requirements. Numerical and experimental simulations, and prototyping, are presented to demonstrate the feasibility of the proposed adaptation scheme to handle network QoS variation in a control loop. The effective results show the promising future of the use of gain adaptation in networked control applications.

Networked control systems (NCS) are in existence for quite some time. The network-induced delays and packet drops; and their effect on control system's performance has been a burning topic for last one decade. Dependability in context of NCS has not got much attention. While it is an important aspect of NCS intended to be used in critical application. The paper reviews the present state of developments in NCS and presents open problems pertaining to dependability of NCS. Solutions to these problems may increase the presence of NCS by many folds and in many fields.

Design, Analysis and Real-time Implementation of Networked Predictive Control Systems

The performance of a networked control system (NCS) is affected directly and indirectly by time delays generated in network communication. This paper addresses these time delays, their effects on system performance and the measures taken in an NCS design. For a time delay that is random but less than one sampling interval T, we model the system as a time-invariant control system with constant time delay T. For a time delay that is random and greater than one sampling interval T, we consider the system as a control system with packet drop and model it as a jump linear control system. Based on the above models, we propose a systematic method to improve the control system quality of performance by choosing a proper sampling interval to reduce data transmission, optimally scheduling to minimise packet loss and optimising controller design in case of packet loss. The simulation results and lab experiments demonstrate that the design method results in high performance in networked real-time control system.

Networked control systems (NCSs), in which controllers and actuators are connected by communication networks, have been utilized in both industrial and consumer applications. In addition, sleep-based energy-efficient network interfaces have been developed for constructing a green networked society. The combination of the NCSs and energy-efficient network interfaces is a promising approach to reduce the power consumption of NCSs. However, sleeping of the network interface results in loss of data to be transmitted between a controller and an actuator. The sleep-induced data loss causes degradation of control performance. Moreover, NCSs originally include network delay for both forward and feedback paths, which also degrades control performance. This paper proposes a time-delay and data-loss compensation method using a modified communication disturbance observer (MCDOB) for NCSs with sleep-based energy-efficient interfaces. The proposed MCDOB can simultaneously compensate for not only the network delay but also sleep-induced data loss as a disturbance, whereas a conventional communication disturbance observer (CDOB) considers only network delay or network-induced data loss and cannot be directly introduced into the NCSs with sleep-based energy-efficient interfaces. Experimental results show that the proposed method with MCDOB outperforms the conventional method without the MCDOB in terms of integral square error (ISE) and communication rate, which indicates the power consumption of network interfaces.

This work is concerned with the design of a controller for networked control system on the basis of the two disk mixed sensitivity problem. To accomplish it, the state feedback decoupling technique is used to reduce the design problem into the one of establishing filter parameters that yield a system satisfying the design specifications. The key point is that here we are concerned with both the stability and performance of the overall networked control system.

Recent publications showed that packet loss significantly reduces the performance of Networked Control Systems (NCS). One approach to increase the reliability of the communication system is to retransmit lost packets. Obviously, such retransmissions take time and thus require to increase the sampling time, what generally degrades the performance. Thus, we raise the question whether it is worth to increase the sampling time to allow more packet transmissions per sampling interval. To answer this question, we present and analyze four different configurations of the transport layer. Finally, with the help of three simple examples, we show that the control performance can be improved by a proper design of the transport layer.

The control problem of networked three-tank system is studied when the data packets can be lost randomly between sensors and controllers, controllers and actuators. Using the theory of vector recovery and state estimation for networked control system, the compensator and state estimator are calculated by solving a linear programming problem and linear matrix inequalities, respectively. Based on the model of three-tank control system, the simulation experiment of networked control system is carried out by Matlab/Simulink and the network/packet-loss is simulated based on TrueTime toolbox. The simulation results show that the method of digital estimator can compensate the influence of packets loss on the performance of control system.

Networked control systems offer significant advantages in terms of reliability, commissioning and maintenance, especially for complex systems. They must be able to withstand delays and data corruption caused by the underlying communication network. Existing results in networked control systems provide varying degrees of robustness. However, cost is also an important factor for real world implementations, which further restricts the bandwidth of the underlying network and complexity of the communication protocol. In this paper we introduce a networked control system method, WMBPNCS, that we have previously proposed, and implement a control system using IEEE 802.15.4 (ZigBee) as its communication protocol, in an attempt to overcome these problems. We find through simulations that performance of our implementation is acceptable even under large amounts of random network delay and data loss.

Networked controlsystems (NCSs) are distributed control system in which sensors, actuators andcontrollers are physically separated and connected through communicationnetworks. NCS represent the evolution of networked control architecturesproviding greater modularity and control decentralization, ease maintenance anddiagnosis and lower cost of implementation. A recent trend in this researchtopic is the development of NCS using wireless networks (WNCS) which enableinteroperability between existing wired and wireless systems. This paperpresents the feasibility analysis of using serial to wireless converter as awireless sensor link in NCS. In order to support this investigation, relevantperformance metrics for wireless control applications such as jitter, timedelay and messages lost are highlighted and calculated to evaluate the wirelessconverter capabilities. In addition the control performance of an implementedmotor control system using the converter is analyzed. Experimental results ledto the conclusion that serial ZigBee device is recommended against theBluetooth as it provided better metrics for control applications. However, bothdevices can be used to implement WNCS providing transmission rates and closedcontrol loop times which are acceptable for NCS applications. Moreover the useof the wireless device delay in the PID controller discretization can improvethe control performance of the system.

DTS: Dynamic TDMA scheduling for Networked Control Systems

For a class of uncertain continuously networked Lurie control systems with both sensor-to-controller time-delay and controller-to-actuator time-delay, the problem of codesigning its observer and fault-tolerant controller based on an event-triggered mechanism under actuator failure is investigated. Firstly, considering that the state of the system cannot be measured directly, an observer is constructed on the controller node. Secondly, to reduce the waste of network bandwidth resources and improve the performance of the network control system, a network control system approach based on event-triggered mechanism is proposed. By introducing the event-triggered mechanism and the actuator fault indication matrix, the Lurie networked control system is modeled as a Lurie system with time-delay using the state augmentation technique to obtain a model of the closed-loop system. Finally, based on Lyapunov stability theory, sufficient condition for the stability of the closed-loop system is obtained, and the design method of the fault-tolerant controller and the observer is given. The obtained results are given in the form of linear matrix inequalities, which are easy to be solved by using the linear matrix inequality toolbox. Finally, the feasibility and effectiveness of the method are illustrated by a simulation example.

Numerous efforts are underway to develop testing and experimentation tools to evaluate the performance of networked control systems (NCS) and supervisory control and data acquisition (SCADA) systems. These tools offer varying levels of fidelity and scale. Yet, researchers lack an experimentation framework for systematic testing and evaluation of NCS reliability and security under a wide range of failure scenarios. In this paper, we propose a modular experimentation framework that integrates the NCS semantics with the DETERLab cyber security experimentation facilities. We develop several attack scenarios with realistic network topology and network traffic configurations to evaluate the impact of denial of service (DoS) attacks on scalar linear systems. We characterize the impact of the attack dynamics on six plants located at various levels in a hierarchical topology. Our results suggest that emulation-based evaluations can provide novel insights about the network-induced security and reliability failures in large scale NCS.

Wireless networked control systems have gained significant popularity due to commissioning and maintenance ease. Currently there are various wireless communication protocols available to accomplish the control networks. Recently, IEEE 802.15.4e protocol for low latency deterministic network has been introduced that shows prominent theoretical characteristics under effective frequency planning to minimize mutual interference. Factory automation, highly exacting from low latency point of view, requires sensors refresh rate not more than of order 10 milliseconds. This new protocol meets such stringent requirement of industrial automation systems. In this paper, we compare the new protocol with its previous version and observe its suitability for industrial networked control systems as a communication protocol. We introduce different LLDN (low latency deterministic network) superframe configurations that show trade-offs among various network parameters. It gives an insight of relationship among various network parameters like sensors refresh rate, number of devices accommodated in network and data payload exchanged between coordinator and end devices with emphasis on different levels of security incorporated.

Networked control systems (NCSs) have attracted much attention in the past decade due to their many advantages and growing number of applications. Different than classic control systems, resources in NCSs, such as network bandwidth and communication energy, are often limited, which degrade the closed-loop system performance and may even cause the system to become unstable. Seeking a desired trade-off between the closed-loop system performance and the limited resources is thus one heated area of research. In this paper, we analyze the trade-off between the sensor-to-controller communication rate and the closed-loop system performance indexed by the conventional LQG control cost. We present and compare several sensor data schedules, and demonstrate that two event-based sensor data schedules provide better trade-off than an optimal offline schedule. Simulation examples are provided to illustrate the theories developed in the paper.