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

[knut.erik.enerstvedt@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@cae.wisc.edu
To:	trnsys-users@cae.wisc.edu
Date:	08/07/2009 07:08 PM
Subject:	TRNSYS-users Digest, Vol 56, Issue 9

---

----- Message from Yeonsook Heo <yeonsook@gatech.edu> on Fri, 7 Aug
2009 08:29:15 -0700 -----

To:	trnsys-users@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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