Voltage sags are one of the main problems in transmission

and distribution grids with high penetration of distributed

generation. This paper proposes a voltage support control scheme

for grid-connected power sources under voltage sags. The control

is based on the injection of reactive current with a variable ratio between

positive and negative sequences. The controller determines,

also, the amount of reactive power needed to restore the dropped

voltage magnitudes to new reference values confined within the

continuous operation limits required in grid codes. These reference

values are chosen in order to guarantee low current injection

when fulfilling the voltage support objective. Selected experimental

results are reported in order to validate the effectiveness of the

proposed control.