Distributed control of electric drives via Ehernet

Sammanfattning: This report presents the work carried out aiming towardsdistributed control of electric drives through a networkcommunication medium with temporal constraints, i.e, Ethernet.A general analysis on time delayed systems is carried out,using state space representation of systems in the discretetime domain. The effect of input time delays is identified andis used in the preceding controller designs. The main hardwareapplication focused in this study is a Brushless DC servomotor, whose speed control loop is closed via a 10 MbpsSwitched Ethernet network. The speed control loop, which isapproximately a decade slower than the current control loop, isopened and interfaced to the network at the sensor/actuatornode. It is closed at the speed controller end at another nodein the same local area network (LAN) forming a distributedcontrol system (DCS).The Proportional Integral (PI) classical controller designtechnique with ample changes in parameter tuning suitable fortime delayed systems is used. Then the standard Smith Predictoris tested, modified with the algebraic design techniqueCoefficient Diagram Method (CDM), which increases the systemdegrees of freedom. Constant control delay is assumed in thelatter designs despite the slight stochastic nature in thetiming data observations. Hence the poor transient performanceof the system is the price for the robustness inherited to thespeed controllers at the design stage. The controllability andobservability of the DCS may be lost, depending on the range inwhich the control delay is varying. However a state feedbackcontroller deploying on-line delay data, obtained by means ofsynchronizing the sensor node and controller node systemclocks, results in an effective compensation scheme for thenetwork induced delays. Hence the full state feedbackcontroller makes he distributed system transient performanceacceptable for servo applications with the help of poleplacement controller design.Further, speed synchronizing controllers have been designedsuch that a speed fluctuation caused by a mechanical loadtorque disturbance on one motor is followed effectively by anyother specified motor in the distributed control network with aminimum tracking or synchronizing error. This type ofperformance is often demanded in many industrial applicationssuch as printing, paper, bagging, pick and place and materialcutting.Keywords:Brushless DC Motor, Control Delay, DistributedMotion Control Systems, Proportional Integral Controller, SmithPredictor, Speed Synchronization, State Feedback Controller,Stochastic Systems, Switched-Ethernet, Synchronizing Error,Time Delayed Systems, Tracking Error