Modified Variable Droop Control Strategy for Improved Primary Frequency Response in Wind Turbine Generators using ROCOF

Frequency control is one of the challenges in wind turbine generation. One frequency control method used by wind turbine generators (WTGs) is droop control. In the droop control method, various strategies have been devised to continually update the droop gain to suit the current situation. This study proposes a modified droop control method that uses the advantages of two variable droop control strategies based on the system frequency deviation: the rate of change of frequency (ROCOF)-based method and the frequency-dependent method. Moreover, limits were set in the droop gain value based on the rotor speed. The proposed ROCOF-based frequency-dependent droop control strategy aims at maximizing the frequency nadir improvement with a quick primary frequency response reaction time while preventing secondary frequency drop or stall of the turbines. These improvements can be used to increase wind penetration in the system, allowing for the reduction of fossil fuel use. The frequency regulation performance of the proposed droop control strategy was compared with other droop control methods in the MATLAB/Simulink environment using a doubly fed induction generator (DFIG) WTG model based on the National Renewable Energy Laboratory Fatigue, Aerodynamics, Structures, and Turbulence model.