Is it possible to use the PID function in a V20 drive using modbus communication? 

I need to send a setpoint and receive feedback from the drive about the motor speed. 

Yes it is possible. Please read this S20 operating instruction manual page 149 you will find MODBUS register numbers for communication.

BTW which master device will control the drive & what is the application?

PISCEAN 2010

Yes it is possible. Please read this S20 operating instruction manual page 149 you will find MODBUS register numbers for communication.

BTW which master device will control the drive & what is the application?

 Thank you for the response!

I will be using an S7-1212C with a CB1241. The application is a ventilation system.