Why do I get an empty Bode plot when using the Model Linearizer App for a Simulink model that represents switching power electronics circuits?

Given is a Simulink model that represents a switching power electronics circuit, whereby also some Simscape blocks are accordingly used. It is possible to use the Model Linearizer App to compute an operating point for particular trimming specifications, but one can see that there is a large error produced by the optimizer used for obtaining the trimming result. However, a trimming operating point can be generated, which can be used to obtain the desirable dynamics of the system.

However, when trying to generate a Bode plot using the latter trimming operating point, then the Model Linearizer App just shows an empty graph, see the following screenshot,

Why do I get an empty Bode plot when using the Model Linearizer App for a Simulink model that represents switching power electronics circuits?

Answer 1

[MathWorks Support Team]

In short, the empty Bode plot based on the generated operating point is expected because the linearization result of zero gain in this case.

In more detail, the trimming workflow may not work with models that represent switching power electronics circuits, because of the discontinuities that are present in the model. For example, the switching power electronics circuit model would lead to a failure in the trimming process. If one opens the computed trimming operating point object in the Model Linearizer by double-clicking it, one would see that the Actual dx may be far from the Desired dx, which means that the trimming result does not converge.

For such type of switching power electronics circuit models, it is recommended to use a snapshot operating point in order to find a steady-state by actually simulating the model. The technical article that summarizes this workflow can be found in the following link,

https://www.mathworks.com/company/technical-articles/estimating-the-frequency-response-of-a-power-electronics-model.html

Moreover, there is a functionality that can identify potential issues in the linearization result which is called "Linearization Advisor", please take a look at the following documentation page,

https://www.mathworks.com/help/slcontrol/ug/identify-and-fix-common-linearization-issues.html

Simply enable the Linearization Advisor through the Model Linearizer, try to generate the Bode plot based on the computed operating point and the Linearization Advisor will provide you with potential issues that the model has in terms of the linearization.

Because of potential discontinuities in the circuit model, the linearization workflow for obtaining the trimming point would not apply for creating a Bode plot in this case. It is recommended to use the frequency response estimation workflow, which is also mentioned in the following technical article,

https://www.mathworks.com/company/technical-articles/estimating-the-frequency-response-of-a-power-electronics-model.html

Moreover, our Product Marketing team has created a short video about the controller tuning workflow for active power factor correction using Simulink Control Design, which would be more appropriate for this application, see the following link accordingly,

https://www.mathworks.com/videos/active-power-factor-correction-1546869199547.html