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VFD Torque Control using a PID controller and Force from a load cell as the process input

Hello,

 

I am unsure if the community can help with this, but I am having some tuning issues with the PID vi in LabVIEW to control a 3-phase motor using Torque Control via a VFD and monitoring using a load cell.

 

I am using Modbus via RS-485 for communication. 

 

My code has a while loop which monitors the Force using a load cell and sends the Force values to a PID vi as the process input with the output range (0 to max torque 8192, mentioned in the COM manual of the VFD) and sends the PID output to the write input of the Modbus for torque command to the VFD.

 

I have tried providing a set force and varying the gains but it seems to be not working to get a tuned PID. I have tried changing the gain but even if I get to lower the overshoot for a particular set force, when I provide another set force it behaves differently. Why can't I tune the PID? Also I have tried the autoTune PID, with no luck, but also I am not sure how to use it or if it can even help for my situation. 

 

I can post an image or a snippet of my code upon request from anyone interested in knowing more about my issue and who is willing to help.

 

Thanks for your time.

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Hello Can you show please your code snippet as i am certified LabVIEW architect

CLA
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Hello ahmed,

 

Thanks for your reply,

 

Here is a snippet of the code which receives the set force to the PID and then sends via Modbus to the VFD for torque control using Force and monitoring the load using a load cell. The set force is sent as a calculated fraction of the end force set based on the input speed and RTA (is french for RTS rated tensile strength). 

 

Also a snippet of how the set force is calculated. I can provide other info as requested. 

 

Thanks, 

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Hello Ahmed,

 

Thank you for your reply.

 

Here is a snippet of my code showing also the subvi which provides a calculated set point at each loop until end force set has been reached to the PID and then via Modbus to write the PID output as a torque input to the VFD.

 

There is a speed and timing discrepancy to reach the end force based on the calculated subvi set value from labview to the PID and the actual timing for the VFD to reach end set force.

 

I am hoping to match the calculated speed in N/s in labview based on force control using the load cells value and the VFDs speed to reach the required torque based on the set force required. Do I need to provide to PID instance before sending to the VFD? force and timing?

 

Thanks,

 

 

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@ikhan123 wrote:

Here is a snippet of my code ....


Please note that a LabVIEW snippet is a special image that turns into real code when pasted into a VI (details). All you have attached so far are plain screenshots that we cannot really debug well, especially if they are truncated and contain loads of local variables with the associated terminal nowhere in sight.

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