MATLAB: Is the step response in Control System Tuner different than when I simulate the model

Question

I am using Control System Tuner on my model to chose the gains of a PID. In Control System Tuner I get a step response that I like but when I update the blocks in my model with the new gains and simulate a step response in Simulink the behavior of my model is different than what I was seeing in the Control System Tuner app. Why is this?

Answer 1

When you use Control System Tuner with a Simulink model, the software computes system responses and tunes controller parameters for a linearization of the model, and thus will have a different step response than your model which may be non-linear. By default, Control System Tuner linearizes at the operating point specified in the model, which comprises the initial state values in the model (the model initial conditions). You can specify one or more alternate operating points for tuning the model. See the link below for details:

http://www.mathworks.com/help/control/ug/specify-operating-point-for-tuning-in-control-system-tuner-app.html