Error with Gain and Phase Margin block in simulink : The linearization I/P O/P block must define a single I/P single O/P system

In the attached file you can see I have used both a bode plot block and a gain and phase margin plot block. In the bode plot block there are no errors while Gain & Phase margin block is showing error when I want to see bode plot. The error is as follows: The linearization I/P O/P block must define a single I/P single O/P system. If the system was not siso then bode plot block would not have worked as well. If you enter the blocks the internal parameters are exactly same as well. Why is the case? How to solve it?

Answer 1

[nick]

Hi Sumaiya,

I understand from your query that you want a resolution for “must define a SISO” error thrown by the "Gain and Phase Margin Plot" block in your Simulink model.

I have simulated your model in R2023a, and the "Gain and Phase Margin Plot" block throws a SISO error even though the model has only one pair of Linearization Input/Output. After investigating further using MATLAB R2023b, I noticed that the "Gain and Phase Margin Plot" block works without any errors on this version of MATLAB. Thus, as a workaround, you can use MATLAB R2023b for the "Gain and Phase Margin Plot" block in your model.

Alternatively, you can use the "Model Linearizer" in the "Apps" tab in Simulink for linearizing the model at the operating point. You can export the obtained linearized model from the "Linear Analysis Workspace" to the "MATLAB workspace" by right-clicking on the model’s name. Then you can use the "margin" function to obtain the gain and phase margin. You may refer to the following documentation to learn more about “margin” function: https:/www.mathworks.com/help/control/ref/dynamicsystem.margin.html

Here is the obtained output from the "Gain and Phase Margin Plot" block:

Hope this helps,

Regards,

Neelanshu