in 1-to-3 phase [passive] conversion with caps motor is not 'harmed' but will operate at somewhere below 80% of the normal 3-phase power ..
as you said, it is pretty common practice, and here are more details on this issue:
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however, much better option is to use a proper ac drive, which is basically single-phase-to-three-phase inverter, and you can get them from, for example, ABB:
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these drives offer soft start, variable speed etc etc and are also manufactured by siemens, telemechanique, sunshine el, and 101 more companies around the world ..
rgds,
ianp