What would be the options to supply a 3-phase motor without using the power lines?
There are a couple ways to supply a VFD during an outage. Which makes the most sense depends on the details of your application. In particular, how long do you need to run during a power outage?

If you need to survive an indefinite-duration outage, you need a generator, period. Any generator should be fine, though you'll need to size it to account for the harmonic content of the VFD. You also won't be able to use line-regenerative braking unless there are other loads on the generator to consume the energy.

Now, if you need to run off the generator exclusively, and never have a power line, you're done. If, however, you need to be able to switch between the power grid and a generator, you have more issues to account for. All generators have a spin-up time long enough that the VFD will trip out before it can switch over. So you need an supply for during that changeover. That's got to be batteries or capacitors, and probably a voltage regulator of some kind.

There are two basic approaches here. One is a UPS of some kind, which puts out AC. You can get a double-conversion UPS, which sources the load all the time. Or you can get a multimode UPS, where your load is sourced from the power grid until there's a disturbance, at which point the UPS switches in to take over.

If all you're backing up is a VFD, however, a UPS is not the best solution. Most VFDs (especially at the power scale you're talking about) have terminals to accept a DC input. A battery string with a voltage regulator can feed DC power into those terminals. This allows for completely bumpless transfer, fewer components, and higher standby efficiency. It's also a completely parallel solution, which is inherently more reliable.

My company makes systems like this, including storage, chargers, and regulators. We can support any power range you need, for any duration required. Contact us at www.bonitron.com and we'll help you out.

(As a footnote, there are cases where batteries aren't the preferred storage mechanism. High voltages, high powers, and short outage durations lend more towards ultracapacitors. For very low energy requirements, simple electrolytic capacitors may be appropriate. For cases where energy-efficient braking and outage ridethru are both required, a bank of ultracaps directly on the bus with no intermediate regulator may be most appropriate. There are a lot of possible variations!)