Specifications

Design Controller Using the Design Tool
3-33
Entering CSTR Manipulated Variable Constraints
If any simulation plot windows are open, close them (to force fresh plots).
Select the T Setpoint 1 scenario. If necessary, set its Controller option to
Unconstrained. Change Duration to 15, and simulate the scenario.
Select the T Setpoint 2 scenario, set its Controller option to MVconstraints, change
its Duration to 15, and simulate it. The results appear in CSTR Outputs, Unconstrained
(1) and MVconstraints (2) and CSTR Manipulated Variable, Unconstrained (1) and
MVconstraints (2).
The larger control horizon and smaller control interval cause the unconstrained
controller to make larger moves (see CSTR Manipulated Variable, Unconstrained (1)
and MVconstraints (2), curve 1). The output settles at the new setpoint in about 5
time units rather than the 10 required previously (compare curve 1 in CSTR Outputs,
Unconstrained (1) and MVconstraints (2) to curve 1 in Blocking Comparison, Outputs).
CSTR Manipulated Variable, Unconstrained (1) and MVconstraints (2) (curve 2) shows
that the Max Up Rate constraint limits the size of the first two moves to 4 degrees.
The third move hits the Maximum constraint at 10 degrees. The coolant temperature
remains saturated at its upper limit for the next 7 control intervals, then slowly moves
back down to its final value.
CSTR Outputs, Unconstrained (1) and MVconstraints (2) (curve 2) shows that the output
response is slower, but still settles at the new setpoint smoothly within about 5 time
units. This demonstrates the anti-windup protection provided automatically by the
Model Predictive Control Toolbox controller.