[TRNSYS-users] PID controller to modulate the opening of a damper

[knut.erik.enerstvedt at niva.no]

Yeonsook,

I am not sure what excactly causes your problem, but I can give you some 
advise on using PID controllers in TRNSYS simulations.

1) Use the controller in mode 0 and with a small time step.
2) Leave the on/off signal (input 3) to 1 unless you need to force the 
controlled equipment to be shut down under certain conditions. The 
controller will still generate a control signal of 0 if that is what the 
PID algorithm predicts.
3) Experiment with the P, I and D coefficients (inputs 7, 8 and 9). If you 
use the Proportional term only, the control signal will often oscillate as 
the set point is met in one time step but not in the next and so on.
4) Be sure to have enough thermal mass in your system (for example tanks 
and pipes) and a sufficiently high thermal capacitance of your building. 
That way, the system will react slower to changes in external and internal 
conditions, and it will be easier for the controller to stabilize.

Hope this helps.

Kind regards,
Knut Erik
 



From:
trnsys-users-request at cae.wisc.edu
To:
trnsys-users at cae.wisc.edu
Date:
08/07/2009 07:08 PM
Subject:
TRNSYS-users Digest, Vol 56, Issue 9



----- Message from Yeonsook Heo <yeonsook at gatech.edu> on Fri, 7 Aug 2009 
08:29:15 -0700 -----
To:
trnsys-users at cae.wisc.edu
Subject:
[TRNSYS-users] PID controller to modulate the opening of a damper
Dear TRNSYS users,
 
I am using PID controller to modulate the damper to control natural 
ventilation coming to a space through an atrium. The problem is that 
control output constantly osciallates from 0 to 1, but never stabilizes at 
a certain value between them. I tried to simulate with different time 
steps, but the results did not change. 
 
Could you help me what possible problems and solutions are for this 
matter?
 
 
Thanks,
Yeonsook

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