[TRNSYS-users] convergence problems with own type (behaviour similar to Controller Type 2b)

["Schreiner, Florian" <florian.schreiner2@student.kit.edu>]

Dear TRNSYS Users,

I have some convergence problems with a new type that I have written.
The type has to compare different temperatures and choose the one which is sufficient to supply a required temperature.
I know that convergence problems occur when two or more temperatures are nearly equal because then the type
oscillates from one iteration to the next and the maximum number of oscillations (iterations) is finally exceeded in one time step without any result.

To solve this problem I tried to be guided by the Differential Controller Type 2b. 
A death band and a maximum allowed number of iterations is used there to reach stability.
Considering the code of Type 2b, I am not really sure if  this type uses values from the previous time step OR from the previous iteration?
Does the function “getOutputValue(i)” deliver a value from the previous iteration OR from the previous time step?
Furthermore there are four outputs in the code, but in TRNSYS there's only one output (the control function itself). 
And only this control function output is linked to the control function input for hysteresis effects in TRNSYS.
But in the code, the other three outputs are also accessed by the “getOutputValue(i)” function.
So I don't really know what's the difference and if values from previous time step are accessed or values from the previous iteration.
  
Just now in my own type, I use the “Dynamic Storage Array” to access values from the previous time step.
But I would rather prefer to access values from the previous iteration to solve my convergence problems.

Maybe someone has already come across this sort of convergence problems or is more familiar to the
code of Type 2b and can explain me how it works.

I need this type to finish my diploma thesis, so I would be great if someone could help.
Thanks in advance!

Best regards,
Florian