In a VSI (Voltage source inverter)
(a) the internal impedance of the DC source is negligible
(b) the internal impedance of the DC source is very very high
(c) the internal impedance of the AC source is negligible
(d) the IGBTs are fired at 0 degrees.
This question was addressed to me in final exam.
This is a very interesting question from Single Phase VSI-1 in section Inverters of Power Electronics