Understanding Smart Sensors - Nomads.usp

Control Techniques 1617.6 Adaptive ControlAdaptive control is a system of advanced process control techniques that iscapable of automatically adjusting or adapting to meet a desired output despiteshifting control objectives and process conditions or unmodeled uncertaintiesin process dynamics [17]. Because of their capacity to learn, neural networkshave the capability to provide adaptive control, but they are not the onlymeans. As shown in Figure 7.8, the difference between the desired performanceand the measured performance in the control system is the starting pointfor the adaptive process [18]. The adaptive system modifies the parameters ofthe adaptive controller to maintain the performance rating close to the desiredvalue.All adaptive control systems have a conventional servo-type feedback loopand an additional loop designed to identify the online process and determinethe parameters to be adjusted on the basis of the process parameters. The additionof an identification algorithm and an outer control loop maintains performancein the presence of disturbances. An indirect adaptive scheme has anadditional outer loop to perform system identification, and it provides access toprocess parameters for monitoring and diagnostics [18].Adaptive control can be obtained in fuzzy logic systems using a controllerthat operates at a higher level to perform tuning and adaptive control functions[19]. Figure 7.9 compares the architecture for that approach to a low-leveldirect closed-loop system. Adjustments that the fuzzy logic controller performsDesiredperformanceDisturbanceReferenceinputAdaptivecontrollerPlantOutputComparisonsystemAdjustmentsystemPerformanceratingmeasureFigure 7.8 Adaptive control system.