HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New MillenniumFuzzy logic rules are used to train the sensor to distinguish thedesignated color and also to compute the sensor output signal. Coloracceptability corresponds to the logic set range of 0 to 1.Model-based ControlThe basic concept of model-based control involves a model of theprocess which is used to calculate a value for the manipulated variable(m) (Fig. 6-9). This value should make the controller variable (x) behave insome desired way. If this is satisfied, then this value of m is utilized.The controller does not use PID components and usually there isonly one tuning parameter, the speed of the controlled variable as itmoves to the setpoint. Initializing the controller with a validated modelis a critical implementation step.The inverse model is used. In standard modeling, the input is setand the response of the output is observed. The inverse model determineswhat input causes a predetermined output response. (Figure 6-10)If the model is exact, an open loop structure could be used. But,most controller models are not exact and they require some feedbackcorrection. The usual approach is to monitor the difference between themodel and the process output and adjust a controller feedback signal.The feedback signal is either a bias to the setpoint or a model coefficient.Modeling TechniquesThree distinct modeling approaches are used:• transfer function,• time series,• nonlinear phenomenological.Figure 6-9. Model-based control©2001 by The Fairmont Press, Inc. All rights reserved.