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?
That's probably about right.
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
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 ..
The old surplus motor trick works very well. See:
A friend acquired a couple of large 3 phase motors from the P&W surplus store in Hartford CT, and it works very well.
work.
AC
and AC
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 =^.^=
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
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