PID controller in Simulink for airplanes

This question is about the PID block in simulink. I use a the 2DOF PID controller block for feedback from an airplane to regulate the speed. The output of this controller is an input to the throttle, so I use upper and lower limits to set as how high the output can be.With the anti windup method set to back calculation, the controller gives a smooth and precise tracking to the reference. However this works well only in a limited case : say my airplane is flying at 650, I have my reference set to 600, it works, or my reference set to 800 it achieves it nicely ; But if I have a reference set to 400 or 1000, it takes forever to get there. Not sure, if varying the gains would necessarily help, because I do limit the output. Is there any way possible for faster response? I should also mention that my upper limit is 1 where as my lower limit is -.2 ..so magnitude wise they are different. Also what is the right way to use the TR (tracking) input? Thanks a lot!

Answer 1

[Paulo Silva]

What's that output you limit? is it the vertical speed? or the control error?

Those limits you have are reached when you have references like 400 or 1000, extreme reference values?

Answer 2

[Sampriti Bhattacharyya]

Paulo, the output of the PID controller is the "delta throttle" means the amount of throttle position I want to change.I am limiting it to -.2 (lower limit) below which the engine thrust would be too low and upper limit of 1. If I go to 400, the lower limit is reached, so the controller constantly outputs -.2. So...I am a bit confused how to fix this.

[Paulo Silva]

in real life it would also take some time to reach such extreme reference values, the lower one would like putting the plane on free fall but you can change your limits on the "delta throttle" so it can reach the reference faster. Just changing the gains won't solve your problem.