Is it possible supply the fan with an external supply on ATV71HC31N4 drive.
Yes, it is possible supply the fan with an external supply, for this you need to change the terminal and supplied the R, S, T, terminal.
The terminals RO, SO & TO are for the supply of the main fans, It is only an AC supply. The purpose of this supply is to have a separate power supply for the fan if the drive is stopped/supplied by DC.
To use RO, SO & TO terminal you must reverse 2 connectors on the fan supply board (i.e. X4 to X1).Refer to attached file.