Out out voltage of 3 phase inverter

if you wire it as a delta, yes.

Being a nervous fella, if I could I'd start with the shaft load reduced or off, and a lower voltage, just to check it behaves.

what is it turning?

M.

Now here is the answer, it doesn't matter a jot. I suppose you want to know why, hold on hard then:

Electric motors have a nominal voltage, this is to limit the no-load current to a sensible value, The "sensible current" depends on the winding inductance, so a 50 Hz motor has more turns than a 60Hz one and a 400Hz motor has very few. If you put 50Hz on a 400Hz motor or transformer, it will take a large no-load current, sufficient to burn it out. If you put more volts on the motor it will again take more current unloaded, which may cause overheating. Take a 400v (delta) motor and connect it star to a supply of 400V, what happens? It turns, it will provide some output power, and generally be a motor. However if you fully mechanically load it, it will probably stall, as the winding inductance is now too high to supply the FLC. Increase the voltage and it will behave as it should.


A motor fed from a VFD can be supplied at some peak voltage, generally above the supply input (because it is sourced from rectified and smoothed DC) usually something like the peak AC input. This doesn't matter and is useful. The important bit is that the motor current is controlled by the VFD, not the voltage. The VFD measures the motor characteristics at set-up, and knows the inductance and some other parameters, and works out the maths to provide pulse widths to simulate its AC nominal currents, see the diagram above. The average of the pulse widths are set to give the average current taken at that part of the mains cycle, simulating the current in a winding (remember this does not start and stop quickly with the pulses) as if the motor were on normal AC. It measures the rotor position between every output pulse (usually by something called the flux vector, measuring the magnetic field in the rotor cage compared to the coil positions) and calculates the width of the pulse needed to give the correct average current to move it the correct angle at the selected running frequency. Is that complex enough?


I have a VFD at home on my lathe (Colchester Master) which takes in single-phase nominal 230V and outputs 3 phases to the motor, rated at 230V in delta. The actual peak voltage to the coils is about 350V, not too far from that during a mains cycle. The motor is 4kW, and I use it between zero and twice its normal speed, ie.100Hz. The VFD can reverse direction too, and can run between 0 RPM and 3000 RPM. The switching is at a few kHz, a bit screechy at times of big load but not bad. The advantage is that I can go at any speed with a knob, change speed whilst turning, and get very low speeds when needed for tapping, and it will plug into a single phase supply (it will blow a 13A fuse at full load fairly easily). The diagram is not really right the sine wave is current, not the pulse voltage, or though of course the two are related.