Fuzzy Frequency Droop Control of DFIG Wind Turbine Generators Adapted to Continuous Changes in Wind Speeds

Without energy storage or reserves, wind turbine generators (WTGs) can provide temporary additional power when participating in frequency regulation (FR) by releasing rotor kinetic energy. Because the FR process is not long, the impact of the changes in the wind speed during FR was not directly considered in most of the previous studies. The field-measured wind speed data were analyzed first, and the results indicate that the wind speed remaining constant during the FR period is a small probability event. Then, a variable-coefficient fuzzy droop control strategy (DC-FLC) is proposed. The DC-FLC modifies the droop control parameter directly according to wind speed variations, which can effectively improve the adaptability of the control strategy to wind speed variations. When exiting FR control, the DC-FLC adopts a smooth exit strategy to solve the problem of smooth switching of maximum power point tracking control and adopts a rotor speed recovery strategy that takes into account the direction of the frequency change, eliminating or delaying the occurrence of the second frequency decrease under unfavorable conditions such as a high wind power penetration rate and continuous wind speed decrease. The comparison of the FR response of the WTG itself proves the superiority of the DC-FLC. The comparison of the FR effects shows that the advantage of using a DC-FLC is significant when the wind speed continues to rise or first decreases and then rises. In situations where the wind speed continues to decrease or rises first and then decreases and the wind power penetration rate is high, the main function of the DC-FLC is to delay the decrease in frequency. The simulation results indicate that under adverse conditions, simply improving the FR response capability of WTGs may not be effective. Moreover, achieving coordination between wind power generation and other FR resources in the system is more important, which is one of the focuses of future research.