Algebraic Loops found only when controller is used

Hello!

I am currently working on a model that runs without problem, I have loopbreakers where I need them, and everything is fine.

However, when I place a PI controller on a centrifuge, I immediately get the error message warning me of an algebraic loop and that inserting a loopbreaker is necessary. Is there a way to work around this?

Also, I would just like to confirm that the data output of the centrifuge is the variable "DS". Is this correct? Thanks again!

Similarly:

If I remove a certain controller that works properly, then place it again, I get an "interface link undefined" between the node and the controller, despite the arrangement being identical and the method used to link them being the same.

Regarding your first post: the reason why a loopbreaker is needed between the PI controller and the centrifuge is that the separation model associated with a centrifuge block is purely algebraic. However, WEST (I assume you're using 2017) is not able to insert one automatically because it should be placed on the 'red' (i.e. non-flux) connection between the two blocks - and the default loopbreaker only work on the state vector (not on individual scalars).
The simplest solution is to place one manually on the outflow of the centrifuge - and, depending on your control loop, also use a separate sensor after the loopbreaker to derive the measurement that is to be fed to the controller.

Hi Enrico,

It might be good idea to create one for the data type connections and add it to a future version of the standard model library.

Best regards,

Youri

Actually, each category (primary and other) should have a corresponding loop breaker model. On top of that (as Youri correctly points out) there should also be a loop breaker model for scalars (cf. Data / Control).

Note that when activating the InsertLoopBreakers option, the software will only be able to insert one particular loop breaker model automatically (the one specified through the LoopBreaker property), so there are several classes of algebraic loop situations that can only be solved by placing the appropriate loop breaker(s) manually.