DC Bus/DC Link Voltage of Grid Connected PV Array

Hi, hope you're all doing great! I have a few questions regarding the DC Link Voltage/DC Bus of a grid connected PV array.

In the simulink model (source: https://www.mathworks.com/help/sps/ug/detailed-model-of-a-100-kw-grid-connected-pv-array.html):

1. When the irradiance, PV voltage, current and power are zero, how is the DC bus being regulated at 500v? As seen in the scope.
2. What actually regulates the DC link/DC bus, the MPPT or the inverter?
3. How is the grid power -0.31 kW (at the start of the simulation when PV power is 0, as seen in the simulink model)? What does this imply?

In the Hybrid DC grid line diagram:

4. If I model the PV, FC, and battery and connect them all to 1 DC bus, how will I regulate this DC

bus?

5. What will the VSC's job be and what will the boost-buck controllers job be to do?

I will greatly appreciate any guidance, thank you kindly.

Grid PV

Grid PV Scope

Hybrid DC Bus