Cannot Find a Good Design in PID Tuner
After adjusting the PID Tuner sliders, sometimes you cannot find a design that meets your design requirements when you analyze the PID Tuner response plots.
How to Fix It
Try a different PID controller type. It is possible that your controller type is not the best choice for your plant or your requirements.
For example, the closed-loop step response of a P- or PD-controlled system can settle on a value that is offset from the setpoint. If you require a zero steady-state offset, adding an integrator (using a PI or PID controller) can give better results.
As another example, sometimes a PI controller does not provide adequate phase margin. You can instead try a PID controller to give the tuning algorithm extra degrees of freedom to satisfy both speed and robustness requirements simultaneously.
To switch controller types, in the controller block dialog box:
Select a different controller type from the Controller drop-down menu.
Click Apply to save the change.
Click Tune to instruct PID Tuner to tune the parameters for the new controller type.
If you cannot find any satisfactory controller with PID Tuner, PID control possibly is not sufficient for your requirements. You can design more complex controllers using Control System Designer.