Frequency Control Capability of a DFIG-Based Wind Farm Using a Simple Linear Gain Droop Control

With additional control loops, the wind turbines (WTs) have the frequency control capability to improve frequency nadir (FN) when a large disturbance occurs. To prevent the rotor speed of WT from reaching the minimum limit during the low wind speeds, a novel kinetic energy (KE) based droop control loop is proposed. In several traditional control loops, the droop gain is presented by a quadratic function of the WT rotor speeds. However, implementing a quadratic function in the generic model of WT is difficult. Therefore, in this study, a new linear-gain droop control loop is proposed for the doubly-fed induction generator (DFIG) based wind farm (WF). In the proposed control loop, the droop gain is a linear function of the WT rotor speeds. By selecting the proper coefficients of the linear function, the proposed linear droop gain can achieve a good approximation to the quadratic droop gain. The performance of the proposed droop control loop is demonstrated based on three wind-speed conditions. To verify the responses of system frequency and WT power output, four indices are developed. The simulation results demonstrate that the frequency control capability of the proposed linear-gain droop control loop is close to that of KE-based droop control loop.