PPT - Feed forward, Cascade and Selected Control

 Page 1


Traditional Advanced Control
Approaches – Feed forward, Cascade
and Selected Control
Page 2


Traditional Advanced Control
Approaches – Feed forward, Cascade
and Selected Control
2-1 Feed Forward Control (FFC)
n Block Diagram
n Design of FFC controllers
n Examples
n Applications
Page 3


Traditional Advanced Control
Approaches – Feed forward, Cascade
and Selected Control
2-1 Feed Forward Control (FFC)
n Block Diagram
n Design of FFC controllers
n Examples
n Applications
Why Feedforward ?
n Advantages of Feedback Control
§ Corrective action is independent of sources of
disturbances
§ No knowledge of process (process model) is required
§ Versatile and robust
n Disadvantages
§ No corrective action until disturbance has affected the
output.  Perfect control is impossible.
§ Nothing can be done about known process disturbance
§ If disturbances occur at a frequency comparable to the
settling time of the process.  Then process may never
settle down.
Page 4


Traditional Advanced Control
Approaches – Feed forward, Cascade
and Selected Control
2-1 Feed Forward Control (FFC)
n Block Diagram
n Design of FFC controllers
n Examples
n Applications
Why Feedforward ?
n Advantages of Feedback Control
§ Corrective action is independent of sources of
disturbances
§ No knowledge of process (process model) is required
§ Versatile and robust
n Disadvantages
§ No corrective action until disturbance has affected the
output.  Perfect control is impossible.
§ Nothing can be done about known process disturbance
§ If disturbances occur at a frequency comparable to the
settling time of the process.  Then process may never
settle down.
Feedforward Control
Feedforward
Controller
Disturbance
Process
Output
Manipulated
Variable
Page 5


Traditional Advanced Control
Approaches – Feed forward, Cascade
and Selected Control
2-1 Feed Forward Control (FFC)
n Block Diagram
n Design of FFC controllers
n Examples
n Applications
Why Feedforward ?
n Advantages of Feedback Control
§ Corrective action is independent of sources of
disturbances
§ No knowledge of process (process model) is required
§ Versatile and robust
n Disadvantages
§ No corrective action until disturbance has affected the
output.  Perfect control is impossible.
§ Nothing can be done about known process disturbance
§ If disturbances occur at a frequency comparable to the
settling time of the process.  Then process may never
settle down.
Feedforward Control
Feedforward
Controller
Disturbance
Process
Output
Manipulated
Variable
Feedforward Control
n Advantages
§ Corrective action is taken as soon as disturbances
arrives.
§ Controlled variable need not be measured.
§ Does not affect the stability of the processes
n Disadvantages
§ Load variable must be measured
§ A process model is required
§ Errors in modeling can result in poor control