I have a similar issue, im using a 5.5Kw induction motor with a G120C inverter connected via PN on a 1215 PLC, i can get the motor to move on the drive commissioning but not on the axis commissioning and if i do it overshoots the position for ages then gives me a positioning fault! 

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Split from Commissioning positioning axis in TIA V13.

Maybe the direction of the encoder or the motor is wrong. When you start a positioning in positive direction, the encoder must be increased.
If it's decreasing invert the motor OR the encoder direction in the configuration of the axis.

Have you set the rampe times in the G120C to 0?

Make shure the motor/inverter is optimized (use motor control panel), before starting the positioining commissioning.