400 Hz

[erik at baigar.de]

> Incidentally, a way to get three phase power at a frequency of your 
> choice is to use a "variable frequency drive".  

Please be careful with this! Have quite some experience in building 
three phase inverters from such small boxes for my various avionics 
projects. 

(1) The normal ones rectify the mains voltage (in EU this gives 
around 320V DC) and from this make PWM outputs on three lines. 
Yes, you can enter voltage and frequency (sometimes even more than 
400Hz) digitally, but the outputs are ALWAYS PWM switching between
0V and 320V in the EU.

Consequence: If you rectify these outputs you will get back your 320V,
completely independent of your settings!

You need to use a device called Sinus-Filter, i.e. a low pass using
caps and Ls to smooth out and get rid of the PWM - only than you 
get the correct three phase.

(2) The small boxes are only for motors (inductive loads). Connecting 
someting else (does not matter whether three phase or not) which e.g.
has got EMC filters at the input containing caps, the relatively high
frequency (e.g. 16kHz, often selectable) will easily toast them leading
to a short.

(3) The PWM-boxes do not isolate from mains, so you will have pretty high
voltages at the PWM outputs with high frequencies which can be a challenge 
for isolations - so even if you set the inveter to 110V only, but power it 
from 240Vmains, the isolation of your device needs to handle the full
320V!

My biggest inverter based on such a small PWM motor drive inverter is
described in my blog (including schematics)...

http://www.baigar.de/TornadoComputerUnit/TimeLine.html#inverter1500

(4) DO NOT use these three phase boxes connecting one output and one
input pin to your device thinking that this is a single phase output.

Creating a "neutral" line at the output of such an inverter can be 
done, but it requires additional components and than you can use 
it as single phase device: Here I used a special transfomer after 
the Sinus filter with input in triangle and output in star configurations.
So I get neutral PLUS insulation to mains...

   Good luck!