Battery+PV; problem with AC inverter effiency loss in DC conexion (battery)

Hi,
I´m doing a model about utily scale PV plus storage with batteries, but I´m having problems with  the inverter effiency loss when I connect the batteries in DC conexion .
Specifically This losses are due to inverter thermal derate DC power loss.
This problem doesn´t happen when I connect the batteries in AC conexion.
 Does anyone know why this problem happens? and which is the solution? 
I´m using the module Longi 540m and the inverter powerelectronics 3270k.
Thanks you.

Hi Jorge,

For DC-connected batteries, DC power from both the battery and the PV array is converted by the inverter on the Inverter input page.

For AC-connected batteries, the battery discharges through a separate inverter with a fixed efficiency that you specify as DC to AC conversion efficiency on the Battery Cell and System input page.

The inverter in the DC-connected battery case may experience more losses when it converts power from both the array and the battery.

Best regards,
Paul.