Networked Control System And Its Application To Three-tank System

A major trend in modern industrial system is to integrate computing. communication,and control into different levels of machine/factory operations and information processes.These distributed control systems are called NETWORKED CONTROL SYSTEMS (NCSs), and havesensors, actuators, and controllers interconnected by communication networks. The changeof communication architecture from point-to-point to this common-bus approach, however,introduces different forms of time-delay uncertainty in the closed-loop dynamics. Thesetime delays come from the time sharing of the communication medium as well as the computationtime required for physical signal coding and communication processing. Moreover, the timedelays in a control application can degrade a system' s performance and cause systeminstability. In order to guarantee the stability and performance of an NCSs, the time delaysdue to the networked communication should be characterized, the impact of network-induceddelays on control performance should be analyzed , and a methodology to further improvethe network and control performance should be investigated. This dissertation analyzed network architectures and protocols for control application,presented NCSs design consideration of network and control parameters, formulated a delayedmodel, solved the controller problem to compensate for distributed communication delays.In order to verify and illustrate the theoretical results, A Internet network is alsoimplemented on a three-tank control system to validate the theoretical and simulationresults. 74To understand the time delays in an NCSs due to networked communication, the mediumaccess control mechanism of the three candidate control networks: ControlNet, DeviceNet,and Ethernet, is discussed in detail, and the key performance parameters are identified.The time-delay characterizations of the network transmission and device processing aretheoretically formulated verified by simulation and experimental analysis. For eachprotocol, we studied the key performance parameters of the corresponding network when usedin a control situation, including network utilization, magnitude of the expected time delay,and characteristics of time delays. Several comparison of static network parameters of thesecontrol networks were also presented. These comparisons provided a first understanding ofthese network protocols and were used as a primary guideline for selecting a network solutionfor control application. The time-delay characterizations of network transmission anddevice processing were then theoretically formulated and verified by simulation andexperimental. Simulation and experimental studies demonstrated the impact ofnetwork-induced delays on control performance. That is, the performance of the same digitalcontroller for the delay-free systems and delayed systems will be different. The avenue for performance improvement utilizes a complete time-delay modeling andcontroller design of NCSs, which could overcome the time-delay uncertainty in an NCSs, andachieve the best control performance. In this dissertation, we analyzed and modeled a NCSswith time-delays. The time delays between sensor to controller and controller to actuatorand the time skews at different devices' sampling instants were considered and includedin the derivation of the continue-time and discrete-time model. The modeling assumption 75and design procedure were practical and based on the aforementioned research result oftime-delay characterization of network systems. The closed-loop NCSs model was first usedas a verification tool for the stability and performance of standard controller whendesigned without considering time delays. Based on the time-delay modeling algorithm, adelayed state-invariable model was formulated for the controller design, for instance, PIDcontroller design or standard LQR controller design. Simulation...