A bit of an old thread but with some interesting comments.
An AC inverter compresser will work so:
Convert 240V AC to 340V DC through a rectifier (remember 240V is RMS voltage so peak is 340V (ish))
Put this DC voltage through inverter to give a 3 phase AC, controllable frequency output.
Adjust frequency to suit load.
Therefore you can't use a bank of batteries to power the compresser, but I suppose in theory at least you could use solar panels to provide the inital DC voltage.
What's with this DC inverter business then?
All in the terminology chaps. These are not DC motors as in Direct Current. More like Digitally Commutated or DC Brushless motors. These use a permanent magnet in the rotor and a 3 phase stator connected to the inverter.
The difference is the permanent magnet as opposed to the electromagnet found in an induction motor. Something about better performance over certain frequencies/load with the permanent magnet.
Think about how a DC (back to Direct Current now) motor works. The alternating magnetic field is produced by swapping round current flow in the rotor via the brushes and the stator provides the constant magnetic field from the permanent magnet. All that happens in the brushless DC motor is the alternating magnetic field is swapped to the stator and permanent magnet to the rotor.
It's development went like this:
Q: How are we going to get a rotating magnetic field now if we can't 'mechanically' reverse current flow?
A: Reverse current flow in the stator.
Q: Can we do that with a DC supply?
A: Hey nonny no my friend because a DC current will never swap round.
Q: Well in that case the job's off.
A: Not so fast young shaver. Let's use an AC inverter to swap it round, tweak it a bit and just to confuse
everyone we'll call it a DC Inverter.
Q: You must be as smart as that bloke Andy from Southampton
A: As smart yes, but not as good looking.
Some BLDC motors are supplied with a DC voltage but they have the nessecary switching gear built in the motor casing but this isn't the case with compressers.
Infomation is a bit hard to find on HVACR inverters and DC inverters but here are a couple of links to help explain my point.
http://en.wikipedia.org/wiki/DC_motor
http://www.atmel.com/dyn/resources/p...ts/doc8138.pdf
http://www.powertecmotors.com/pdf/fm...PXA_041116.pdf Page 2-11 shows a brushless DC drive block diagram (just incase anyone doubts me!)
Enjoy!!
Andy.