LVRT current injection

[danilorj]

Hey guys

I'm sending this graph to show you the behavior of the PCC voltage during a sag event with and without reactive power injection. Grid codes establish that the distributed generator units should remain connect to the utility grid during voltage sag events and at the same time providing reactive power to support the grid voltage. This is called LVRT (low voltage ride through).
I don't know exactly what 'support the grid voltage' means. Can you explain it?
This graph has been obtained by simulation, I don't know whether it is right or not.
The voltage sag applied was 0.5 p.u.
I don't know exactly what is the purpose of this reactive injection, is it only to keep the voltage sag regulated at 0.5 p.u ?

 

[Anna Conda]

support the grid voltge, means try to hold it up, 0.5pu is just what you got, better apparatus would give higher than 0.5

 

[danilorj]

and if the voltage falls to 0 V? Do I still have to inject reactive power to support the 0 V voltage? But the Q power is calculated by the voltage and it's zero...??

 

[Anna Conda]

Sensibly, once the voltage goes below say 100V for more than 3 cycles, all bets are off and the equip disconnects until proper mains is restored....

 

[danilorj]

Yes.. but there are some grid codes which state that the distributed generator must stay connected to the main utility even if the voltage at the point of common coupling drops to zero. That is why I am asking. So if it drops to zero, I do nothing and wait till it recover to the value before the fault within the range set in the grid code. And if it's not, I cease energy. Is that what you mean?