Frequency Regulation by Distributed Energy Resource Inverters Based on Parabolic Droop Curve

In the last few decades, distributed energy resources (DERs) based on renewables have experienced rapid growth due to the abundance and low emissions of renewable energy. As the role of these renewable DERs grows in power systems, the grid frequency characteristic becomes softer due to the reduced system inertia. Standards and international grid codes have been issued for grid interconnection of DER inverters with frequency regulation capability, which expects DER system to regulate the grid frequency by adjusting the active power injected into the grid. Therefore, the renewable DERs should not operate at maximum power point so it can increase or reduce power output according to the set slope to participate in frequency regulation. Traditional frequency droop control methods adjust the target power at the same rate no matter the frequency deviation is large or small, which does not fully utilize the rapid response of power electronic converters in DERs. This paper proposed a new frequency regulation method based on a parabolic droop curve, which makes better use of the rapidity and flexibility of DER inverters by restoring the frequency slower when the frequency deviation is small and restoring the frequency faster when the frequency deviation is large.