Generally, the equivalent grid impedance depends on the operating mode of the inverter. In PQ mode, you may determine an equivalent impedance referred to the DC side based on the the injected P, Q, and the voltage. Anyway, it is important to state the study that will be consequently conducted.

The approx. equivalent resistance of the (grid+grid side converter)=

(Vdc bus)^2/Pg..

where Pg is the active power injected to the grid..

Thank you for your answer , in which case this impedace can be neglected i.e. very small value

Moien, if it looks like an infinite busbar, it's got zero impedance. Simples

Mustafa, depends on how good is the inverter's control of the DC voltage. If it maintains near constant voltage over the load range, it's an infinite busbar. If not, it ain't

Thanks James for your answer

Let's asuume that the Inverter has a good control strategy for DC voltage side at rectified mode i.e. zero impedance. And its very closed to DC-DC converter place i.e the resistance between them can be neglected. And the DC-DC converter coil has approximately zero resistance. Due think all these reasons can be enugh to energy circulating between the Inverter dc terminals and capacitor across dc-dc converter input terminals.

Thanks

Truly Yours