Hi
I have a VFD secondary chilled water pumps connected to the BMS, my problem is that once the VFD's are running the communication between the DDC panels are lost. Could anyone help me sort out this problem? I have done the proper earthing but the problem still exist. The VFD's are inside the MCC.

WHat's the HP of the VFD?
What's the proximity of the VFD to the DDC?
Have you looked at possibe dips in the power to the DDC when the VFD starts?

Possible routes are:
RF
EMI
Power line pollution *
Power line sags
Ground loops

Might try a filter at the VFD. What is voltage/current requirements for the VFD?

* is probably likey

VFD is a big contributor of harmonics that causes CB tripping, relays or PLC disturbance. Install a passive harmonic filter it will improve your hamonic level as well as impromving your power factor.

Hi..
In that case do check the profibus or field bus card .The problem could be from card .