Yes, there is possibility for overmodulation. Overmodulation increases output voltage up to hexagon form, which means that RMS value as well as fundamental harmonic will increase. Also 3rd harmonic to the motor is generated, but it is not a problem, because motor is 3-phase symetrical and so 3rd harmonic is attenuated in the motor.
Bear in mind that this overmodulation can add only few percents (5-6%) comparing to non-overmodulated (circular form) shape.
See extract page from ATV900 manual. The same is available for ATV600.

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