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V350-J-TR20 >>> Modbus communication with 2 VFDs

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Dear Unitronics Support Team,



I am new to PLC. I have issue while writing more than one data on different drives.

Model no. :- V350-35-TR20
Visilogic 9.7.24
VFD :- ABB (ACS550 5.5HP and 3.5HP) Qty :- 2Nos. Slave ID 1 for Big HP drive and Slave ID 2 for Small HP drive.
Tried on Baud rate :- 9600 and 57600 only. rest all cant communicate.

Application :- To automatically increase the speed of both motors slowly and simultaneously after given time. 
for Big HP VFD     >>>> Speed1 = Slow speed , Speed2 = Medium speed and Speed3 = High Speed.
for Small HP VFD >>>> Speed4 = Slow speed , Speed5 = Medium speed and Speed6 = High Speed.

When both the Drive Starts, 
Big and small HP VFD will take speed1 and speed4 respectively for say T0=30sec.
After T0=30sec Big and small HP VFD will take speed2 and speed5 resp. for again T1=30sec and 
After T1=30sec Big and small HP VFD will take speed3 and speed6 resp. and will continue to run till stop comand is given. 

Observation :- 
1) Both the VFDs communicated with PLC via RS485 MODBUS. 
2) When i manually increase or decrease the speed both VFDs work properly
3) As soon as simultaneous data is given, only one VFD gets the data and other one fetch the previously stored data.
4) I did increased Baud rate of all Modbus communicating devices. So it is writing much faster but the last value speed3 and speed6 in between this two speed there is a random delay.
5) At all these instant "Function in Progress" bit is high after writing one data on Big HP drive(Slave ID 1). 
So i think because of this "Function in Progress" bit PLC can't write other data on the Small HP drive(Slave ID 2). 
And the time taken for "Function in Progress" bit to turn off is random. It varies from 5 sec to 12 sec.

I can tolerate delay of 1sec between Slave ID 1 (Big HP) and Slave ID 2 (Small Drive). So is there any solution or trick to solve this issue?


Thanking you!!!

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