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Modelica DES Control Loop Parameters

asked 2023-02-13 12:07:10 -0600

updated 2023-02-14 17:07:29 -0600

Hi,

I am hoping for some more detailed advice for control loop settings in District Energy System models in Modelica. I have followed the guidance given with the PID controller documentation (https://simulationresearch.lbl.gov/mo...) but I need more help.

At the broadest level I need guidance on how to think about the Ti parameter for all the different elements of my DES model. I have many elements with control loops (timeseries loads, susbstation heat exchangers, pumps, plant devices like boilers and chillers) and all of them are controlled with PI controllers.

My timeseries loads change every T=600s so I thought maybe I should use that as the Ti term for all the parts of the system. But I have studied the other controllers and they definitely do not react every T=600s, its sometimes more often and sometimes less often.

Should I use the same Ti for all the controllers? If not how do I think about "tuning" a model with so many different control loops?

The control loop performance makes a huge difference in the feasibility of running my model. I have 150 buildings (timeseries loads) in my DES and if any of element of the system slows down because of controller error it significantly degrades the ability to even run the model. I want to run an 8760 hr simulation but right now I am looking at about a three day run time which is unacceptable for debugging purposes.

Thanks! Graham

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answered 2023-02-14 17:36:19 -0600

The statement "My timeseries loads change every T=600s so I thought maybe I should use that as the Ti term for all the parts of the system" indicates a misunderstanding. The time constant of the controller, Ti, needs to be appropriate for the dynamics of the feedback control loop to which the time series load is just an input, or a disturbance. The value of Ti is not dependent on how fast your time series change. Generally, the default values for Ti (and k) as entered for the template models in the Buildings library should work or may need only minor tuning.

I suggest you check for one of your 150 buildings whether they are appropriate, tune them if needed, and these settings should typically then also work for the other buildings because of the way the dynamic response of HVAC equipment is configured in the Buildings library.

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Asked: 2023-02-13 12:07:10 -0600

Seen: 136 times

Last updated: Feb 14 '23