Dear sir

I have two identical PM240-2 drives for machine slewing operation and both are controlled by PLC. I need to configure master -slave operation between drives. What are parameters I have to change please give details. CU 310-2DP used for drives, since CU 310-2 DP is a single axis control, I will ready to transfer data using PLC. 

Why you don't use a CU320-2 with CUA Adapters? This should be cheaper and you don't have and delay by an communication bus.

But for coupling you can do a simple torque coupling for rigid mechanics, or speed coupling with Static or Position synchronism for weak mechanics.

a.). for a simple torque coupling, I would transfer the r79 from the MASTER to the SLAVE.

b.)  for a speed coupling, you can send MASTER.r62 and MASTER.r79 to the PLC and to the SLAVE. Inside the SLAVE you should give the r62 after the ramp generator (p1155). Inside the PLC you can do a P-controller of r79 of MASTER and SLAVE.r79. If the values are different, you will add the output of the P-controller as additional speed setpoint (then the torques are synchornized.

c.) position synchroinization: Then you can use the technology objects of a S7-1500(T).

In the cases a.) b.), If one drive makes an fault, you should handle this inside the PLC. (check the status words r899 from both drives).. In case c.) If should be sufficient, if one drive has an TO- error, that you make a reaction.

... sensorless, I suppose you use VECTOR. 

There the droop functionalitäy is available (also a recommendation from the Technology Team).

7.4.4.4 Droop Function

https://support.industry.siemens.com/cs/ww/en/view/109764530