Research On Frequency Regulation Strategy Of Doubly-fed Induction Generator In Microgrid

Benefit from the national energy structure adjustment, wind power generation develops rapidly. The invention of microgrid has solved the grid interconnection of small-scale decentralized wind farms, improving the utilization of wind power. The system frequency fluctuation has been getting serious in microgrid, on account of the proportion of wind power increased, especially in the islanded mode. Lots of energy storage elements are used in microgrid in order to improve system stability, which causes the operating cost of microgrid increases significantly. In this paper, through the research of frequency regulation strategy of the doubly-fed induction generator(DFIG) in microgrid, the frequency regulation capability of DFIG and the stability of microgrid are tried to enhance yet the system operating costs is reduced.First of all, different DFIG frequency regulation strategies are researched based on the analysis of DFIG operating principle, which focuses on the control principle and frequency regulation capability mean while summaries and comparisons are completed.Secondly, the problem of frequency second drop during frequency regulation is researched. The DFIG frequency regulation process is divided into action stage and recovery stage based on the amount of DFIG active power output through the analysis of DFIG integrate frequency inertia control dynamic operation process. A solution by adding a frequency second drop control module is proposed which could make the DFIG active power fallen move backward. The problem of system frequency second drop is solved, the stability of microgrid is balanced, the speed of DFIG rotor is recovered and the frequency regulation capability of the integrated inertial control efficiently is promoted by the method came up with in this paper.Thirdly, the DFIG operation and control with different wind speeds are analyzed. A subsection control frequency regulation strategy with different wind speeds combined the applicable conditions of different DFIG frequency control strategies are proposed comparing the frequency character differences between microgrid and regular power grid. Rotor speed control is used in medium wind speed areas. Integrated inertial control is used in the rated wind speed area. Short-term overload pitch angle control is used in high wind speed area. The foundation of sector is divided and choice of frequency regulation strategy is analyzed.Finally, the influence of the fluctuation of the wind speed on the control strategy switching in subsection control is studied. The wind speed, rotor speed, active power, pitch angle are chosen as the reference variables of fuzzy logic control, which generates the wind turbine frequency regulation action permissive signal. The influence of the fluctuation of the wind speed is eliminated, completing a set of DFIG frequency regulation strategies.In this paper, the research improves DFIG frequency regulation capability with different wind speeds. The advantage of different frequency regulation strategies operates sufficiently, assuring the DFIG running safety and improving the stability of microgrid.