Coordinated Frequency Control of a Doubly-Fed Induction Generator and Battery Using the Flexible Power Reference

As increasing the penetration level of wind power, a power system operator requires the frequency support to a wind turbine generator (WTG). To support the frequency control, the conventional frequency control schemes adopt a fixed gain or the variable gain in the frequency deviation loops, but these schemes conduct during the operating region of the rotor speed of a WTG. Thus, the additional device needs to support the frequency control when the rotor speed of a WTG is out of the operating range. This paper proposes the coordinated frequency control scheme of a WTG and battery to enhance the frequency nadir when a large disturbance occurs in a power system. The WTG and battery are in charge of different roles. The proposed frequency control scheme of a WTG uses a droop loop with a variable gain depending on the rotor speed and frequency deviation. In addition, the battery discharges the stored energy depending on the state of charge and the rotor speed of a WTG. The performance of the proposed scheme is investigated in IEEE 14-bus system. As the results, the proposed scheme can improve the frequency nadir for a synchronous generator trip by releasing more stored energy.