From the screenshot of Simulink model attached by you, it is not clear what the circuit is trying to simulate and how the PI inner and outer control loops are working. But, upon investigating the model, I found some potential reasons that are causing the singularity error.
This error mainly occurs when the solver is not able to find a solution for the circuit through iterative methods. In your case, this happens because your circuit has many “open-circuited” paths and many of the components have floating teminals as shown in the below given figure. (Note: Here , the term ”floating terminals” means the terminals that are not connected anywhere.)
Cause of error:
Circuit contains open-circuited paths ,floating terminals and short circuited pulsed voltage source.
Suggestions to fix the error:
Generally, no path of the circuit is kept floating or open circuited. But if your application demands that, connect a high value resistance across the floating terminals and ground.As a next step, look around for all the open circuited paths in your circuits and close the circuit with high value resistance in series.
I hope this answers your question !
