Feedforward and Cascade Control Examples

Consider a cylindrical tank with an adjustable inlet flow that is controlled by a valve. The inlet flow rate is not currently measured but there is a level measurement that shows how much fluid has been added to the tank. The outlet flow is also not currently measured and the outlet pump flow is adjusted manually by an operator. The outlet flow is a combination of the pumped water outlet and an unmeasured leak. A new flow transmitter has been acquired to improve the liquid level control and reject either input pressure disturbances ΔPi or outlet flow disturbances m.out. Evaluate the performance difference by installing the flow transmitter on the inlet flow line or installing the flow transmitter on the outlet flow line. For the inlet flow line installation, develop a feedforward and cascade controller. For the outlet flow line installation, add a feedforward element to the level controller. The objective of this exercise is to develop a controller that can maintain a certain water level by automatically adjusting the inlet flow rate. Comment on the performance differences for cases A-C. Case A (Feedforward Control): Install flow transmitter on inlet flow line and use as a feedforward to the level controller. Case B (Cascade Control): Install flow transmitter on inlet flow line and develop flow controller as an inner loop to the level controller. Case C (Feedforward Control): Install flow transmitter on outlet flow line and use as a feedforward to the level controller. See http://apmonitor.com/pdc/index.php/Ma...