Reactive power control for voltage support during type C voltage-sags

Grid faults are one of the most severe perturbations to deal with in grid connected systems. To support the grid under voltage-sags (dips), different reactive power control strategies are needed depending on the type of grid fault. One of the possible objectives when supporting the grid voltage under type C voltage sags could be to avoid undervoltage in the faulted phases and over-voltage in the non-faulted phase. Therefore, the fault can ride-through the perturbation and the system disconnection can be avoided. This may be accomplished by injecting positive sequence reactive power to raise the voltages and negative sequence reactive power to equalize them. In this work, a detailed mathematical description is introduced to limit the voltage in the phase that do not suffers the voltage-sag just below over-voltage limit, while increasing as much as possible the other two faulted phases. This voltage support service is limited by the maximum rated current. Selected simulation results are provided to understand the proposed reactive power control during type C voltage-sags.