CP1L-M60 PID VFD control

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I'm trying to create a regulator for keeping the speed of a motor match that of another. My feedback is pulses per second, converted to rpm or m/s. My output is an absolute frequency 0 to 1FFF (hex) representing 0-100% hertz. 

How do I configure a PID or PIDAT block to regulate this? My attempts have all resulted in weird data or the MV being 0 to something far to low.

//Kind regards, me


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I have (currently) a program to convert the encoders pulses to rpm. m/s not in practice yet cause I dont have any belts connected to it, so a fixed 10-ratio is in place for that. But the RPM should be fairly correct.

I attach some picture prints of my program, both the sensor reading and regulator control.

And I did try autotune but the motor still goes on and off priodically and does not keep around a value.

//Kind regards.







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I found some relatively good working parameters... Tho I dunno why or how to tune them further... Also, Autotune fails horribly...

+1 P = #0500
+2 I = #0010
+3 D = #0010
+4 T = #0064
+5 = #000C
+6 = #1515
+7 = #0000
+8 = #2000
+9 = #0000
... = #0000

Any ideas on how to tune it?
Setpoint is RPM
Feedback is RPM
Output is a value 0-2000 hex corresponding to 0-100 Hz
RPM is roughly given by the formula RPM = Hz* (2 / poles) * 60, poles in this case being 4.
But lots of factors impact RPM, like load. Also, the Frequency Drive is slow to change, with internal ramp times, so its a bit hard for the PID to keep up
So, to maintain a certain rpm, the output needs to stay "on" at a given level +- a couple of 0.x hz.

//Kind regards for any feedback.

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IMHO you are making this task more complex than need be.

Many of todays VFD's have built-in PID routines that are available.

You would send an analog signal from the MASTER to the FOLLOWER VFD and use the PID setup in the FOLLOWER VFD, no need to mess sround with trying to do it in the PLC.

You haven't stated which model VFD you are using so don't know for sure if it has built-in PID.


My 2 Cents  

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The machine I'm Sourcing the RPM from is not connected to the control network. So I have no "Master", hence follower is a bit out of the question.
VFD in question is a Danfoss FC51

Edit: But the current idea is to simply rely on the RPM to Frequency formula and hope that the result is close enough.

Edited by Roze

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