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'[EE]: Microchip AN on vvvf motor control'
2002\09\27@115842 by Chris Loiacono

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Has anyone looked at microchip's an 843 lately?
It's a nice example of a variable voltage-variable frequency drive for
three-phase induction motors.

It is shown with a three-phase source that is rectified and filtered.
I began thinking (scary, eh?!) that this could be fed by a 2 wire single
phase line also...and rectified with even less parts...

couldn't it?

Assuming line current is not an issue, this would result in a 3-phase
induction motor controller that could be run from a single phase line. I
don't believe I've ever seen such a product...
It seems there would be nice demand for such a thing since many places do
not have 3-phase power available....Hmmmm

Am I on to something here, or am I overlooking the obvious - or not so
obvious?

Chris

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2002\09\27@130305 by Dave Tweed

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Chris Loiacono <.....chrisKILLspamspam@spam@MAIL2ASI.COM> wrote:
> Has anyone looked at microchip's an 843 lately?
> It's a nice example of a variable voltage-variable frequency drive for
> three-phase induction motors.
>
> It is shown with a three-phase source that is rectified and filtered.
> I began thinking (scary, eh?!) that this could be fed by a 2 wire single
> phase line also...and rectified with even less parts...
>
> couldn't it?
>
> Assuming line current is not an issue, this would result in a 3-phase
> induction motor controller that could be run from a single phase line.
> I don't believe I've ever seen such a product...
> It seems there would be nice demand for such a thing since many places do
> not have 3-phase power available....Hmmmm
>
> Am I on to something here, or am I overlooking the obvious - or not so
> obvious?

Your single-phase AC to DC converter needs to be able to store enough
energy (BIG capacitors) to supply significant load currents at times when
the single-phase line is at or near zero.

Since 3-phase power is typically used for motors > 1 HP and other
electrical loads > 1 KW, line current is *most definitely* an issue!

I was just recently thinking about this issue when the capacitor went bad
in my 1.5 HP capacitor-start pool pump, and I was wondering if I could
replace it with a solid-state circuit to shift the phase for the starting
winding. I realized that no matter what, some sort of energy storage device
would be needed, so I just replaced the capacitor.

-- Dave Tweed

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2002\09\27@135529 by Chris Loiacono

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>> Assuming line current is not an issue, this would result in
>> a 3-phase
>> induction motor controller that could be run from a single
>> phase line.

>(BIG capacitors) to supply significant load currents
> at times when the single-phase line is at or near zero.

So if the capacitors are less costly than a phase converter this could be
worthwhile....

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2002\09\27@135931 by Morgan Olsson

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Dave Tweed wrote:
>3-phase induction motor controller that could be run from a single phase line. I don't believe I've ever seen such a product...

There is plenty of them, and several manufacturers to say the least...
I recently have looked around for VFD:s...

Google for VFD drives
VFD = Variable Frequency Drives

Low power units are usually one phase in, high power usually three phase, ranges overlap.


I found simple v/f VFD are so cheap theese days it is no win in building them oneself, even for series production.  For example Hitachi L100 is a nice simple one phase in v/f VFD, available in 200, 400 and 750W.  SJ100 has added vector control (a kind of sensorless rpm control) and brake.

The expensive VFD:s have nice algoritms for exact rpm, torque control, and power savings.  Some also have positioning algorithms built-in, and at least one network type (RS485, Devicenet...)

There are even some that do clean sine output so they can be used to drive motors thruogh hundreds meters long standard cables with no problem - while doing decent sensorless rpm feedback and control.  True sine also does not have the power loss problems in the motor as PWM VFD:s (making energy waste and motor power degradation), and des not have the problem with bearing wear due to induced currents.  Cost more initailly, but saves energy, motor wear, service cost, thus total cost.  Targetted mainly at Pumpand fan driving for primarily energy optimization, and noise and wear reduction.  NFO Drives are specialised in this, and Siemens also have some sine converters.

/Morgan

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