VSD (Inverter) current measurement on 3 motor phases
Something does, in fact, exist on the market, and it's not too
  expensive, either. Take a look at the Allegro Microsystems ACS770. –
  Felthry


Hi Felthry,
Thanks for the info on that device, it looks like the solution, so I'm going to:


Order the ACS770 evaluation board
Buy a low pass filter and a signal isolator
Hook it up to a single motor output phase on a 7.5kW inverter and motor
Analyse the signal with a PC capture card &amp; digital meter


Thanks again!