I have the following setup:
1xMultipluss II 48/5000
1x 5kW grid tied PV inverter connected to the ACout 1 of the Multipluss II
1x BYD B-BOX 10 battery
Grid is conneted to the ACin of the Multipluss II and the grid tied PV inverter and loads are connected to the ACout 1. The Multiplus II is configured as an ESS system.
My problem is as follows: If I physically disconnect the grid from the ACin, the system works perfect. If I connect the grid to the ACin, what happens is that frequency in the ACout1 starts to change and the grid tied inverter stops inverting since frequency is out of range. This happens at any SOC of the battery and even at night when the PV invertir is not working. As long as I understand, ACin frequency and ACout1 frequency shoud be always the same, but this is not the case. Frequency variations goes from 48 Hz to 53 Hz (big changes in short time). I can also see the LEDs flikering sometimes. The main problem is that the PV inverter stops inverting due to changes in frequency. Does anyone have any idea why this is happening and how could I solve this problem. Thank you in advanced.