[SOLVED] Online impedance estimation

[danilorj]

Hey guys

I'm reading an article called "Online grid impedance estimation for single-phase grid-connected systems using PQ variations". I'm sending it attached.
In page 3 it is said that "...the difficulty in the estimation of Zg is that the voltage source of the grid (Vs) is immeasurable..."
Why? Can someone explain it to me?

 

[D.A.(Tony)Stewart]

The difficulty in the estimation of Zg using is that the voltage source of the grid (Vs) is immeasurable.
.
VPCC = Ig*Zg +Vs

The difficulty is turning off the switch for all the grid current, as Ig is used everywhere, not just your location.


IMHO comments.
It is a classical ESR method except the grid distributes the problem, so the author localizes it by choosing 2 operating points. Normally 5% drop is allowed for distribution losses from transformer, so this already implies a certain ESR for the rated current of distribution feeder.