[TRNSYS-users] RE- PID controller: Digital or Continuous? (??)

[Thibaut VITTE]

Type 22 & 23 are quite different :
Type 22 doesn't model really a PID controller. It is an 'ideal' 
controller that uses iterations made by TRNSYS to reach convergence. It 
tests a control value and sees the resulting error, and then adjusts the 
value for the next iteration untill it reaches  the maximum error given 
by user.
It is interesting as it models a  variable controller without the hassle 
of tuning the parameters of a PID controller. But the convergence is 
quite erratic to obtain and it can be stuck with systems with great 
inertia, depending on the timestep, etc. Personally I try it on my 
models, and then use a PID because I can't get convergence.

Type23 models a PID in 'real life', ie non iterative with 'mode 0'.  
Whether it's digital or analog, well, I'd say it's analog but it doesn't 
matter, as in the vast majority of the cases the timestep used will be 
far greater than the sampling of the PID. It doesn't use its own 
timestep. And as far as I know, it cannot be used to guess the 
parameters that will be used on the real controller, but just to obtain 
the right control for the simulation.

Hope this helps.

Thibaut