Voltage and current imbalance on VFD output
Voltage and current imbalance on VFD output
(OP)
We are developing a dynamometer stand for durability testing of a hybrid vehicle driveline, which includes on-board PWM inverter and PM motor. Can anybody recommend a commercially available monitoring system which would detect voltage and current imbalances on inverter output? We can not use any inverter internal signals and must use an external monitoring provisions.





RE: Voltage and current imbalance on VFD output
For voltage(s), I use a low pass filter and a differential probe. Set the low pass filter frequency to 1 Hz. That will give you the V/Hz number directly and any change will be readily visible.
NI's LabView is relatively easy to build the monitoring functions in. I'm afraid that is the nearest a standard equipment you can get. Flexible and easy to extend when you need to.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Voltage and current imbalance on VFD output
RE: Voltage and current imbalance on VFD output
Are you interested in the complex waveforms? I try to avoid them when checking motors and drives. But, of course, I need to look at them in detail when checking switching patterns and "modulator", which can be anything these days, mostly SW.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Voltage and current imbalance on VFD output
This is a good reference piece on the subject, albeit slightly biased.
h
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RE: Voltage and current imbalance on VFD output
Also, have you used a current probe with yours? I don't have one and have often wondered whether it would be worth the investment.
RE: Voltage and current imbalance on VFD output
Yes I used a current probe, but not the one from Fluke. A friend of mine is the rep for AEMC and they make most of the current probes sold by everyone else, so I used a flexible one he got for me as a "sample"
http://
They aren't cheap though, I have to warn you.
Huh, funny that I never noticed (or paid attention to) the double image. Wish I had mine back so I could look at it again
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RE: Voltage and current imbalance on VFD output
If everything is perfect you will see a circle otherwise quite deviations quite easy to analyse. Many older papers on PWM AC motor control use this kind of display.
RE: Voltage and current imbalance on VFD output
Current imbalance is much more likely and probably reflects imbalanced impedances in the leads and motor.
RE: Voltage and current imbalance on VFD output
You brought an interesting point. The voltage and current imbalance measurement was a part of customer requirements to provide an early indication of potential e-motor problems during durability testing. We might limit our design to current imbalance monitoring only. I tend to agree that voltage imbalance would indicate inverter rather than motor problems.
RE: Voltage and current imbalance on VFD output