Unbalanced voltage references for three phase asymmetrical power flow in LV grids

[andreabragantini]

Hi folks,
I am trying to simulate a MV/LV substation (5kV-400V) with unbalanced feeders. My grid model mirrors a real LV network where the MV side of the transformer has some relevant unbalances due to the nature of the MV municipality grid.
I therefore need to represent this unbalance as input to the power flow. At the moment, i am able only to set (vm_pu, va_degree) in the external grid elements.

Do you know if there is a way to set (vm_a_pu, vm_b_pu, vm_c_pu) and (va_a_degree, va_b_degree, va_c_degree) instead?

I actually don't understand why it was done this way in the first place, why assuming the MV grid to be perfectly balanced?

Thanks to anyone willing to help