convert 48vDC into 230vAC 3phase
From a battery bank of 48VDC I would like to power 3 230vAC 3ph 10hp motors to power a large vessel.


It would be more convenient if you specified the motors in watts rather than horse-power but we can do the conversion: 10 HP x 0.75 kW/HP = 7.5 kW per motor so about 22 kW total.

From \$ P = VI \$ we can calculate the required current at 48 V if your inverters and VFDs were 100% efficient. \$ I = \frac {P}{V} = \frac {22k}{48} = 460 \ \mathrm A \$. This is not hobby current.


  Would two 10 kW inverters work for this?


Your "schematic" suggests that you want to run two single-phase inverters with their outputs referenced to battery negative to generate a three-phase supply to feed the VFDs. There are several problems with this. The most obvious is that any off-the-shelf inverters are unlikely to be synchronised so you won't have a constant phase angle between them. The losses will be high too.

If I had to do this job I would look at feeding DC directly into the VFD DC bus.



Figure 1. A simplified schematic of a VFD. Note that the drive uses DC internally. This opens the possibility of supplying power directly to the DC link. Source: Natural Resources Canada.

By series connecting your batteries to give the DC bus voltage of \$ 208 \sqrt 2 \$ for 120 / 208 V (North America) or \$ 400 \sqrt 2 \$ for 230 / 400 V (Europe) you would eliminate the inverters and associated losses and reduce the current to more manageable values.

You may be able to feed the DC in using tow of the input terminals. The diodes will sort out the polarity correctly. This has the advantage that the soft-start circuit for the initial capacitor power up (not shown) will still be operatational. Potential problems are that the drive may detect a loss of phase, may detect that it's not AC and since the diodes are working 50% harder than they would if the power was coming in on three terminals rather than two.

You could check with the manufacturers or you might find a drive rated for this type of setup. Note that many drives are designed to share the DC bus / link to conserve energy. While one is braking it can generate back onto the DC bus / link and other motors can use the power.