Voltage support control algorithm based on reactive power injection for grid-tied converters under unbalanced grid conditions

Nowadays power generation is transitioning from conventional synchronous generators (SG) to inverter-based resources (IBR) based on renewable energy sources. These power plants are mainly connected to power systems through voltage source converters. Compared to synchronous generators, IBRs lack inertia during disturbances. Therefore, appropriate control measures must be implemented to prevent large-scale chain trips during fault conditions such as voltage sags. The traditional approach to raising voltage involves injecting reactive current that is proportional to the voltage sag. Current grid codes set the linear relationship between the voltage droop and the reactive current, without providing optimized voltage support in unbalanced voltage. Therefore, an appropriate method is needed to utilize the 3-phase unbalanced voltage condition by applying it according to the grid code. With this in mind, this paper proposes a control algorithm for compensating PCC voltage under 3-phase unbalanced voltage conditions.