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Thread: How a VFD/VSD works
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27th Nov 2021, 01:10 PM #1Most Valued Member
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How a VFD/VSD works
Really good explanation of how a VFD/VSD works
https://m.youtube.com/watch?v=yEPe7RDtkgo
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27th Nov 2021, 07:47 PM #2
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28th Nov 2021, 09:13 AM #3Member: Blue and white apron brigade
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It's pretty difficult to explain VFDs without a lot of words, and any explanations with fewer words will usually leave a lot of gaps. I've had to do this many times, mostly at mens sheds when I visit them regarding dust extractor and inevitably end up attempting to explain how using a 3P with VFD impeller can be used to extract more air from a shed. It's easy to say. "higher frequency - higher speed" but explaining just how it does this gets into muddy waters fairly quickly. Some of the blokes don't really know what "frequency" means or have a very limited understanding of ordinary AC.
In my VFDs4Newbies PDF I don't even bother to explain how they work. Instead I just focus on functional/limitation/installlation aspects
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29th Nov 2021, 02:17 PM #4Golden Member
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I agree with Bob, forget how it works and just use it. I use that method when we are doing dust extraction seminars in sheds and have never had anyone trying to question the how and the what when I explain the book is about 100 pages long.
CHRIS
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29th Nov 2021, 02:27 PM #5Member: Blue and white apron brigade
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I've have had one person in an audience in about 10 years asks me how VFDs work. It turned out he already knew the answer and was just checking if I knew. I told him to come and see me about after the presentation and that's when he told me.
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29th Nov 2021, 07:34 PM #6Golden Member
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I thought that was an excellent explanation.
Given a 3 phase VFD has 3 groups of components (diodes, capacitor, IGBT) and a 1 phase only 2 groups (capacitor, IGBT) why are these things in such relatively big boxes?
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29th Nov 2021, 08:07 PM #7Most Valued Member
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Single phase input units also have a rectifier stage.
Why is it so big, short answer is heat control.
The individual power transistors represented in the video may in reality be made of several devices ganged together for current handling.
If you pull one apart most of the the space is occupied by the power transistors, heat sink and fan.
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29th Nov 2021, 08:09 PM #8Member: Blue and white apron brigade
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A small but not invaluable consideration is access.
These are both 3HP VFDs the one on the left is a Powtran the other is an HY
IMG_2172.jpg
I just find it a lot easier to work on the one with the bigger terminals
BTW the smaller Powtrans are just as cramped as the HYs.
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30th Nov 2021, 01:57 AM #9
There is a lot more to it than just three groups of components !
Yes there are diodes and capacitors, there is also AC to DC to AC conversions along with frequency control. Think about how you get a three phase AC output from a single phase input. Plus all the control circuitry.
I agree with Bob ! The KISS principle wins.Best Regards:
Baron J.
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30th Nov 2021, 09:38 AM #10Most Valued Member
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Easier to just say:
2 ways to vary speed of ac motor is to:
Vary number of poles in motor, or
Vary frequency to motor.
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