What is causing my algebraic loop?

I have a somewhat complex model utilizing the general blockset, Specialized Power Systems, and Simscape Electrical physical systems. I am receiving an error that I have an algebraic loop, containing blocks that contain persistent states, which are not allowed in algebraic loops. I have seen answers explaining that these blocks tend to be integrators, Stateflow charts, Matlab function blocks, and physical systems circuits. Of those things, I only have the physical systems circuit. The physical systems circuit contains capacitors which could count as "persistent states", but if that is the cause, I do not know the solution. The error message is copied below. Can anyone help me spot the cause of the error?
Edit: After digging further, the identified loop goes Voltage Measurement -> Gain -> Subtract -> Gain -> Controlled Current Source. The Controlled Current Source does not directly interact with the Voltage Measurement. I don't see loop here..
'Full_Model_2/Control/Voltage Loop/Solver Configuration' or the model referenced by it contains a block that updates persistent or state variables while computing outputs and is not supported in an algebraic loop. It is in an algebraic loop with the following blocks.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/powergui/EquivalentModel1/State-Space' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Converter 3/Voltage Measurement/do not delete this gain' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 3/Gain1' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Product' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1, 2) of 'Full_Model_2/Control/LM5170/Current Loop 3/Subtract' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 3/Gain' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 3/Saturation' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Converter 2/Voltage Measurement/do not delete this gain' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 2/Gain1' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1, 2) of 'Full_Model_2/Control/LM5170/Current Loop 2/Subtract' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 2/Gain' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 2/Saturation' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Converter 1/Voltage Measurement/do not delete this gain' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 1/Gain1' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/Vbus^UF/do not delete this gain' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/Voltage Loop/Solver Configuration' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (2) of 'Full_Model_2/Control/Voltage Loop/Solver Configuration' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (2, 3) of 'Full_Model_2/Control/Voltage Loop/Solver Configuration' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1, 2) of 'Full_Model_2/Control/LM5170/Current Loop 1/Subtract' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 1/Gain' are involved in the loop.
Component:Simulink | Category:Model error
Input ports (1) of 'Full_Model_2/Control/LM5170/Current Loop 1/Saturation' are involved in the loop.
Component:Simulink | Category:Model error

4 comentarios

James Tursa
James Tursa el 12 de En. de 2022
Algebraic loop can sometimes be caused by feedback without a delay. I.e., feeding the output back as an input without any delay, essentially using the current state as an input to calculate the current state. You can sometimes fix this by adding a delay in the output that feeds back into the input.
Jamie Shaffer
Jamie Shaffer el 13 de En. de 2022
I'll look into this. I'm very confused by this issue, I didn't mention this in the above description but the model worked as-is for a very long time. I made a change recently and received an error (did not record what or why), with creating an algebraic loop suggested by Simulink as the solution. I clicked a "fix" button on the suggestion and didn't know what I was getting myself into. The "fix" seems to have broken the model that previously worked.
I'll consider adding the wait block, but I worry that will ruin the accuracy of the model. I'll also try re-creating the model in a new environment to see if it's a case of a bugged setting somewhere that I haven't found.
Jamie Shaffer
Jamie Shaffer el 13 de En. de 2022
Editada: Jamie Shaffer el 13 de En. de 2022
I've commented out possible causes and discovered the "Algebraic Loops" window that highlights involved blocks. The identified loop goes Voltage Measurement -> Gain -> Subtract -> Gain -> Controlled current source. The Powergui block is also somehow involved. The controlled current source does not interact directly with the Voltage Measurement. I don't see a loop here..
Ankit
Ankit el 14 de En. de 2022
if you can't share model, could you please share some screenshots? it would be easy to find out the root cause. Solution is already mentioned by @James Tursa

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Respuestas (1)

Jamie Shaffer
Jamie Shaffer el 14 de En. de 2022

0 votos

I replaced a piece of the loop that was modeled with a Specialized Power Systems circuit with a transfer function block and the Algebraic loop disappeared. I believe this to be a bug in the solver.

Productos

Versión

R2021b

Preguntada:

el 12 de En. de 2022

Respondida:

el 14 de En. de 2022

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