Simulink with control system designer: Step response is completely flat.

Hello, I have Matlab R2018b and I am trying to use the controlSystemDesigner on a Simulink configuration I have created.

My plant is P(s) = and I have set the compensator, sensor block to 1 and the disturbance, measurement noise to a constant equal to 0 in order to start the design process. Here is the configuration:

My issue, as you can see, is thta for some reason the step response from r to y is completely flat. On the other hand, if I open the controlSystemDesigner using simply the command:

controlSystemDesigner('step', p_drone);

I get a step response which is absolutely different (and it is, I believe, the correct one). I would expect the two step responses to be the same. There is obviously something wrong but I cannot figure out what. Please keep in mind this is the first time I am using the controlSystemDesigner and Simulink. The documentation has not been of much help either.

Answer 1

[Paul]

The block diagram has an Open-loop Input at the input to the plant (on the line marked "u + d") so the response from any input to the "left" of that point will be zero. Also, the diagram has an Open-loop Output at the output of the plant (on the line marked "v") so any output to the "right" of that point will also be zero in response to any input to the plant. Based on the diagram, it looks like you should be looking at the step response from the u+d to v to see the step response of the plant.

I'm not sure what's going on with the response that's the output from from the controlSystemDesigner command, but for sure it's not the step response of P(s) = 2/s^2. I'm not that familiar with the controlSystemDesigner command, but from its doc page I don't even see how that command provided anything but an error. So I'm confused by that as well.

[Ilias Koutroumpas]

Thank you so much, simply by trying random things I figured out the problem were the open loop input(s)/output(s) and I fixed it. As for your comment on the step response, you are right, this is not the step response of the plant alone. It is the step response of the plant with the feedback. I get the same thing through the simlink as well, so I guess it has to be correct.