I used to work for Siemens and went through the training for this drive (but never actually commissioned one before I left). I was told that the requirement for a high power source was total, as in all the way back to the utility, not just from the local transformer. The reason they require that is because if you connect it to a local or portable generator with low relative power and low impedance, the harmonics that the active front end puts into the line gets extreme. you also must have somewhere for the power to go, as in a grid with other consumers attached.
Why someone would assume you can regenerate back into a small power source that may not have anywhere else to send the power is beyond me, It's not as though one can push the electrical power back into the generator and have it spit fuel back into the tank! But as can be witnessed in these forums, some people implement technology without thought to engineering.
So basically it's what we call a CYA statement. They are attempting to make people think and ask questions first, or eat it because they didn't when it doesn't work out. But I thought their wording left something to be desired, it may be a translation issue. Siemens' engineers in Germany tended to assume that readers would know the context and allow for translation errors. We had to learn not to take everything literally and ask for clarification a lot. You may be wise to do so as well. The local salesman may not know the answer, but keep pushing and you will find an engineer that will.
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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