VFD motor feedback?

[winnie]

Thanks for the update. The number of times I've chased measurement errors....

When you push the motor into saturation you see increased magnetization current and magnetizing losses.

But probably more importantly you get increased harmonic distortion of drive current. Any harmonic current flow will create its own harmonic rotating field which causes losses.

You might try capturing current traces of the drive frequency waveform (not carrier, output) to see if harmonic content changes.

Jon

 

[petersonra]

Some drives have what's called a boost setting so that at lower frequencies the voltage is actually increased somewhat.

 

[Jraef]

Can we assume that you have performed a proper auto tune procedure on the drive with the motor attached? If so, was it a static or rotating auto tune?

 

[winnie]

Can we assume that you have performed a proper auto tune procedure on the drive with the motor attached? If so, was it a static or rotating auto tune?

Would one do an autotune if programming for simple V/Hz control?

-Jon

 

[Jraef]

Would one do an autotune if programming for simple V/Hz control?

-Jon

I’ve been recommending it for the last few years now. What I was told is that the latest generation of IIGBTs are switching 10x as fast as the previous generation, so that has effects on the motor equivalent circuit regardless of the expected performance of the drive. In more than one case where my motor was “acting strange” even in V/Hz control, doing an autotune (at the suggestion from Tech Support) solved it. So since then I just do it regardless.

 

[SiriusC1024]

Offline autotuning was done after inputting motor parameters. I always autotune as a matter of course during installation or troubleshooting.

I've found that the parameters adjusted by autotuning can still affect operation in constant V/Hz mode. Toshiba VF-AS3. Conceptually it shouldn't, but it does. One time I adjusted slip frequency gain by a larger margin to see what it did. Motor wouldn't start. Unfortunately, no changes to an autotuned parameter help. The only thing that does is V/Hz ratio.

Automatic torque boost is disabled.

 

[SiriusC1024]

Here's a dual channel reading of voltage across T1-T2 with a simultaneous current reading through T1.

New item by SiriusC1024

photos.app.goo.gl

 

[SiriusC1024]

... that has effects on the motor equivalent circuit regardless of the expected performance of the drive.

There are values for the motor equivalent circuit per manufacturer datasheet.

WYE CONN EQ CKT PER PHASE:
R1 = .00662
X1 = .0657
R2 = .00528
X2 = .0660
XM = 1.84

I've been curious how these are relevant to the end-user. Is this something that I should be paying attention to?

 

[petersonra]

Would one do an autotune if programming for simple V/Hz control?

-Jon

It doesn't seem to matter if it's volts for Hertz but if you're trying to run it in sensorless vector mode it makes a big difference. I have started up vfds and not bother to do the tuning because I was just going to run it in volts per Hertz mode and it runs fine. Later someone decides it would be a good idea to run in sensorless vector mode because someone told them it would save energy and it runs noticeably bad unless you tune it first.

 

[synchro]

Here's a dual channel reading of voltage across T1-T2 with a simultaneous current reading through T1.

New item by SiriusC1024

photos.app.goo.gl

When you used the STL120 probe using the alligator clip did the measured RMS voltage change or did it stay about the same as when you were measuring using the COM input? Just asking to verify that you're seeing the same discrepancy on the measured voltage vs. what would be expected.

 

[SiriusC1024]

When you used the STL120 probe using the alligator clip did the measured RMS voltage change or did it stay about the same as when you were measuring using the COM input? Just asking to verify that you're seeing the same discrepancy on the measured voltage vs. what would be expected.

Yes it changed. Higher voltage with neutral to COM.

 

[SiriusC1024]

I solved the problem. Input voltage sensed by the VFD was incorrect. 476V supply (with motor load drawing down voltage from 480V nominal) read out as 453V. After confirming reasonable supply voltage stability at all loads, I adjusted the parameter to disable this voltage compensation.

The drive was outputting an increased duty cycle to offset what was sensed as a large supply voltage drop. This caused overvoltage to the motor, leading to stator saturation and heating.

- Thank you

 

[zbang]

Glad you found a work-around, but now it gets to why the VFD was seeing a low voltage.

Oh, document this well for the next person.