Adnano

Sorry for the late reply; it's been busy here.
That's probably the same as running 11 kW firmware on a 7.2 kW model. It will likely work, except that it won't protect itself from loads over 7.2 kW.
Twin means exactly that: it has hardware and firmware to support an extra relay and output terminals. You can adjust settings for how and when the extra output comes on.

Finally i have got this resolved, 
The issue was existing in the resistor between op amp output and negative input, having the value 7.5 kOhm
Thanks everyone for the brilliant collaboration

Thus it worked fine before that?
What charge rates did you have before that happened?
If in USE mode without LAN cable it won't charge at the set Amps, then either your BMS or Inverter may have a fault.
Check that program code 02 is set equal to or higher than code 11, else it defaults to the lower one set in 02

If in Li mode, the BMS should auto set code 02 to the battery's max charge current. If it doesn't then you have a faulty comms cable or the two are not communicating properly.

My understanding is that it's only used for battery charging (only utility battery charging for low PV voltage models). The problem is that the bus voltage depends on many factors, such as loads and solar power, and the battery needs a very carefully controlled voltage to get the desired current into the battery when charging it. The DC-DC converter has a fixed ratio between high voltage side and battery voltage. This ratio can be  8:1 or 7:1 or various fixed values in between for various 48 V models. Varying the duty cycle of the isolating transformer drive does not change this ratio. In fact, the DC-DC converter is fed fixed 50% duty cycle (with dead time) square waves from the SG3525 chip.
So the buck converter is used to vary the voltage between the bus voltage and the high side of the DC-DC converter, and this to the battery voltage and thus the battery charge current. You can think of the high side of the DC-DC converter as the battery, transformed up by the turns ratio of the isolating transformer. So if the battery is at 50.0 V and the turns ratio is 7.0:1, then it's effectively a 350 V battery to be charged. Say the bus voltage is 400 V; that 50 V gap is dropped in a low loss manner by the buck stage. Effectively, the buck stage IS the battery charger, just operating at high voltage.
When power flow is away from the battery, this stage does not boost, but instead switches off and the flywheel diode allows power to pass through unaltered (1:1). It must get tricky if conditions are such that the power flow is alternating between charging and discharging the battery. I assume that the battery can't instantaneously support the load in that scenario, and has to wait a few tens of milliseconds for the bus voltage to fall to the transformed battery voltage.

Finally i have got this resolved, 
The issue was existing in the resistor between op amp output and negative input, having the value 7.5 kOhm
Thanks everyone for the brilliant collaboration

Finally i have got this resolved, 
The issue was existing in the resistor between op amp output and negative input, having the value 7.5 kOhm
Thanks everyone for the brilliant collaboration

The voltage between +Vc and -Vc is correct = 24V
The output of phase A is a +12V which is causing the 530V
I don't know the source of this voltage 

I think that this one allows for exporting of power, so it must (or should) have all the regulatory approvals that go along with that.
My guess is that the topology is very similar to that of Axperts, and it's just a matter of how you control the power flow by adjusting the various PWM signals.
There seems to be a lot less information about the Must inverters compared to the Axperts.