Learning Forum

[suraj9735]

Dear All,

I have added an ACT extension (PID Thermostat) in ANSYS Mechanical to control the temperature of my model. I have some question about this extension.

1) What does it mean by the Setpoint Type as-"Use Model Entity as Setpoint" and Setpoint Offset.

2) What would be the initial guess for Kp, Ki, Kd? I started with Kp, setting others are zero and try to tune the value, but the problem is, for one guess it takes half an hour to run the case, That seems inefficient way to tune the PID value. I am new in PID control.

3) I also don't know the logic the program uses and unable to write APDL scripting for PID control.

 

If it's possible, could you please tell me how to tune the PID value in an efficient way!

Thank you!

[Rob]

We can't open attachments, so please repost images. What documentation comes with the ACT? It's likely that the k terms are control functions so should be covered in PID theory? 

[suraj9735]

I want to know how do ANSYS users apply PID control in their simulation?

1) By writing the code of Auto Tuning/Manual Tuning.

2) They use third-party application/Extension like MATLAB/Pid Thermostat.

If you have any reference to apply PID control in Ansys Mechanical, Kindly share with me!

 

You can find the documentation of the PID Thermostat extension from here (https://catalog.ansys.com/product/5b3bc6857a2f9a5c90d32e9a/pid-thermostat-con#download)

[peteroznewman]

I haven't used the ANSYS ACT PID Controller you have, but I found this general guidance on Google.  Where it says distubance, that would be a step change in the temperature.

To tune a PID use the following steps:

1. Set all gains to zero.


2. Increase the P gain until the response to a disturbance is steady oscillation.


3. Increase the D gain until the the oscillations go away (i.e. it's critically damped).


4. Repeat steps 2 and 3 until increasing the D gain does not stop the oscillations.


5. Set P and D to the last stable values.


6. Increase the I gain until it brings you to the setpoint with the number of oscillations desired (normally zero but a quicker response can be had if you don't mind a couple oscillations of overshoot)

What disturbance you use depends on the system the controller is attached to. Normally moving the system by hand away from the setpoint and letting go is enough. If the oscillations grow bigger and bigger then you need to reduce the P gain.

If you set the D gain too high the system will begin to chatter (vibrate at a higher frequency than the P gain oscillations). If this happens, reduce the D gain until it stops.

===============================================================

Here is another opinion on tuning...

Set all gains to 0.

Increase Kd until the system oscillates.

Reduce Kd by a factor of 2-4.

Set Kp to about 1% of Kd.

Increase Kp until oscillations start.

Decrease Kp by a factor of 2-4.

Set Ki to about 1% of Kp.

Increase Ki until oscillations start.

Decrease Ki by a factor of 2-4.

[suraj9735]

Thanks for your help!

Could you please do an example with PID Thermostat in ANSYS Mechanical and try to control the temperature (180 deg) of the face of a simple cube (for example).

I have some more condition

1) Initial temperature=22 deg

2) Time duration= 600 s (can be adjusted if it does not reach to 180 deg)

3) Maximum Power= 2000 W.

 

I played with the given example in PID Thermostat extension to understand the logic of Heat Source/Sink power calculation logic, but unable to understand. There is no setting to limit the maximum power of the heater.

You can download the archived file example that comes with documentation of PID Thermostat from here.