Single phase 220 to 3 phase 220 conversion? how-to

[mook Johnson]

I've seen those static 3 phase generators and was wondering how they work.

I would look at using a triple half bridge and convert the single phase AC
to DC and PWM that it through a 1:1:1 transformer.


Is there a simpler solution than that? Some fancy transformer wiring and AC
capacitors or something?

 

[Tim Wescott]

I've seen those static 3 phase generators and was wondering how they work.

I would look at using a triple half bridge and convert the single phase AC
to DC and PWM that it through a 1:1:1 transformer.
That's probably about right.

Is there a simpler solution than that? Some fancy transformer wiring and AC
capacitors or something?

Define "simple". One very common method is to use a 3-phase machine
with 220V single phase on one winding; it'll generate the other two legs
on it's own. This is commonly done by hobbyists with 3-phase motors
with a start capacitor added on, although there are dedicated rotary
3-phase converters. This sounds beastly and inefficient, but when you
start talking about the energy storage necessary for a 60Hz 10HP motor
using a big spinning chunk of iron starts sounding pretty good.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[sparc]

I've seen those static 3 phase generators and was wondering how they work.

I would look at using a triple half bridge and convert the single phase AC
to DC and PWM that it through a 1:1:1 transformer.


Is there a simpler solution than that? Some fancy transformer wiring and AC
capacitors or something?

You could use three single phase inverters ...each based on a DSP sine
wave generation tech to generate ...what else but a sine wave output on
each of the inverters. All you need to do is fire these inverters 120
degrees apart and voila you have 3 phase power from a single phase
source ! ....simple enough ? ....try it

Hope you have a budget for millions of burnt up MOSFETS ...

Alternatively, you could drive a 3 phase alternator with a single phase
motor ..

 

[Barry Lennox]

I've seen those static 3 phase generators and was wondering how they work.

I would look at using a triple half bridge and convert the single phase AC
to DC and PWM that it through a 1:1:1 transformer.


Is there a simpler solution than that? Some fancy transformer wiring and AC
capacitors or something?

The old surplus motor trick works very well. See:

http://www.woodweb.com/knowledge_base/Building_a_rotary_phase_converter.html

http://www.metalwebnews.com/howto/phase-converter/phase-converter.html

http://www.laserfx.com/Backstage.LaserFX.com/Hobby/PhaseConvert.html

A friend acquired a couple of large 3 phase motors from the P&W
surplus store in Hartford CT, and it works very well.

 

[colin]

You could use three single phase inverters ...each based on a DSP sine
wave generation tech to generate ...what else but a sine wave output on
each of the inverters. All you need to do is fire these inverters 120
degrees apart and voila you have 3 phase power from a single phase
source ! ....simple enough ? ....try it

Hope you have a budget for millions of burnt up MOSFETS ...

Alternatively, you could drive a 3 phase alternator with a single phase
motor ..

There are microcontrollers with pwm outputs wich can generate all the
required gate pulses for 3 phase,
There are also integrated 600v 3 phase mosfet bridges with integral drivers.
Sounds so simple, when I get around to it I may build myself one of these,
maybe by then someone will publish a design and code if it hasnt been done
already.

Colin =^.^=

 

[Paul E. Schoen]

I've seen those static 3 phase generators and was wondering how they
work.

I would look at using a triple half bridge and convert the single phase
AC to DC and PWM that it through a 1:1:1 transformer.


Is there a simpler solution than that? Some fancy transformer wiring and
AC capacitors or something?

I made a 3 phase converter from an inductor, a capacitor, and some power
resistors. Basically, you use RC and LC values to generate 60 degrees phase
shift lagging and leading. There are other tricks you can do with
transformers. Once you have a phase angle, you can generate any phase you
want.


V1 --------------------+--------------+
C1 | | L1
+--|(----+ +---UUU---+
| |
| ----- ----- |
A O--+-| R1 |--------+------| R2 |---+--O C
----- | -----
|
V2 ----------------------------+--O B

I used something like 70 uF for C1, 100 mH for L1, and 26 ohms for R1 and
R2. I think XC1 = XL1 = R1 = R2. You actually need less than 220 VAC for V1
to V2, so I used a variable autotransformer (variac). I produced 208 VAC
from 120 VAC single phase. I had a big inductor and some motor capacitors,
and 2000 Watt heaters for R1 and R2, so my rig is capable of about 2000
watts, but you have to be able to adjust the resistance to match the load.
For running a three phase motor, it is not too critical, but it does run
smoother when the phases are well balanced.

It is a good project for a simulator like Tina or Spice. I also tried
adding a center tapped autotransformer across A, V1, and C (or perhaps A,
B, and C). If you greatly increase the resistance, the voltage from A to C
approaches infinity! Of course, the capacitor or inductor will break down
first, but I got some good sparks when I tried it. The simulator just
showed some huge voltage build-up when I ran a transient analysis.

Solid state PWM VF drives are really the best way to go, but a static
converter works well for some purposes.

Paul