Paralleling two ISUs ACS880 mulitdrives
I have two ISUs powering the same DC bus, together with two inverters in a multidrive setup. Charging and connecting both units to the bus works fine but as soon as they start modulating, one of the unit trips on earth leakage or overcurrent (sometimes right-away, sometimes after a while, sometimes ISU 1, sometimes ISU 2)
I have followed the instructions of the manual Parallel connected ACS880-207 IGBT supply units system description. 3AXD50000032517. Which requires having an isolation transformer in between and setting both units in voltage droop mode. I also send the same voltage setpoint to both ISUs and the load-sharing seems to work fine as they both share 50% of the total power. Unfortunately, as stated before one of the ISUs eventually trips. I can't see any measured current that would cause an overcurrent and the voltage always stays within +-3 volts.
The only thing I deviate from the manual is that the ISUs don't have a BCU but a ZCU control unit. Neither I use DDCS communication. I have a higher level PLC that sends the voltage setpoints to both ISUs via EtherCat.
Thank you in advance.