1. Lecture 5 – IVP, Feed Forward Control
ChE 433 DPCL
Lecture 5 – IVP, Feed Forward Control
Experiment 3
Wiring Problems
Feedfoward Control
Pressure Control

2. Experiment 3
We are having problems understanding the last part, the IVP controller.

4. IVP Control The IVP controller should be the slowest of all.
Acts as a “supervisory” control loop around the whole process.
Other Problem:
We are having problems connecting the wires correctly.
Solution: When we finish wiring, go “Online” with Control Studio.

7. Feedfoward Control
Just what does ISA say?
Control in which information concerning one or more variable that can disturb the controlled variable is converted, outside of any feedback loop, into corrective action to minimize deviations of the controlled variable.
Lets try to outsmart the controller.

8. Three feedfoward algorithms:
Feedfoward Control
If we know that the controlled variable, PV, is significantly changed by another variable, why not change the manipulated variable,OUT, before the controlled variable senses the change? That way we can moved the output anticipating the PV change.
Three feedfoward algorithms:
Steady State Model
Dynamic Model
Impulse Feedfoward

9. Steady State Feedfoward Control
Steady State Model, what we will do in the lab
Develop a process mass, energy balance:
The thought process ...
We know if we increase the hot water flow to the exchanger, we need more cold, cooling, water.
Balance doesn't have to be precise ...
If we increase the hot water flow be so much, we need to increase the cold water flow by about the same amount, assuming same deltaT.

10. Steady State Feedfoward Control
We should be careful not to get too aggressive with the amount, FF_GAIN. Too much will cause over correction that can be more upsetting than no feedfoward at all.
Many FF attempts fail because the action is too aggressive.

11. Dynamic Feedfoward Control
Dynamic Model – The system dynamics may respond differently to a load change, hot water flow, than to a change in TC manipulated variable, OUT, or cold water flow.

15. Dynamic Feedfoward Control
Lead time constant = time constant of the controlled variable, PV, in response to the manipulated variable, OUT.
Lag time constant = time constant of the controlled variable, PV, in response to the load, FT.

16. Impulse Feedfoward Control
Control Technique does not directly manipulate the output, rather modifies the set point. See Chapter 4 of Process Control, A Perspective.

17. Feedfoward Implementation
Three ways:
Add FF signal to the output
Multiply FF signal to the output
Set Point modification, also Smith Predictor et. al.
Watch outs & problems with FF:
What happened if we put the controller in manual?
Can we still have direct control of the valve?
Too many tuning settings to change. Too complicated.

18. Feedfoward Implementation
How do we do FF in DeltaV?
We will test the Steady State Method
on Experiment 2, Heat Exchanger:
Wire a simple feed forward control, where the output of the hot water flow transmitter, FT2-1 is connected to FF_VAL input of TC2-3 control block.
For TC2-3 controller attributes set:
FF_ENABLE = True
FF_SCALE = 0 to 1.0 GPM
Adjust the feed forward gain, FF_Gain