Simulink PID controller apparently doing nothing

Here is my open loop system.

I run the model and plot it in the workspace

subplot(1,2,1)
plot(FV)
ylim([-1 1.5])
xlabel('time (min)')
ylabel('F/V, 1/min')
title('F/V vs. time')

subplot(1,2,2)
plot(CB)
ylim([-1 1.5])
xlabel('time (min)')
ylabel('C_{B} (mol/Liter)')
title('C_{B} vs. time')

Next, I add a PID controller. P = 1, I = 1, and D = 0 (as per the homework instructions)

I run the output again in the workspace

subplot(1,2,1)
plot(FV1)
ylim([-1 1.5])
xlabel('time (min)')
ylabel('F/V, 1/min')
title('F/V vs. time')

subplot(1,2,2)
plot(CB2)
ylim([-1 1.5])
xlabel('time (min)')
ylabel('C_{B} (mol/Liter)')
title('C_{B} vs. time')

I'm not seeing any response that would indicate a controller, in fact, all that happens is that the concentration of B reaches a higher steady state with the controller. I haven't used a controller before, so I wonder if I am doing something incorrectly. Thanks

As a side note, I also get this message

Warning: Using a default value of 0.2 for maximum step
size.  The simulation step size will be equal to or less
than this value.  You can disable this diagnostic by
setting 'Automatic solver parameter selection'
diagnostic to 'none' in the Diagnostics page of the
configuration parameters dialog

Answer 1

[Arkadiy Turevskiy]

I cannot reproduce this behavior. When I run your setup, I definitely see closed-loop response getting to 1 in steady-state. Maybe there is some sort of issue with variable names somehow getting overridden? Try using scopes instead of "to workspace" blocks and see if you get the same results.

I am attaching the model that shows everything working fine.(created in 15b)

[Rick]

I don't know how to open your model to see what you did

[Arkadiy Turevskiy]

what release are you using? i.e., 14b, 12a?