Small-signal Stability Analysis And Participation Frequency Control Strategies For Doubly-fed Wind Turbine Generation System

With the development of wind power technology and the high proportion of windpower penetration in the power system, the demand for wind turbines integrated into thepower gird is getting increasingly high. On the one hand, the wind generator is requiredto maintain its stability at the end of the grid or in poor grid environment; On the otherhand, it is hoped to have the ability to participate in grid frequency regulation asconventional power generator when large-scale wind power is integrated. This project isconsidered from the perspective of the wind turbine itself to study its stability after thepower grid suffered a small disturbance and to research its participation capability ingrid frequency regulation. This research has important practical significance to improvethe grid frequency stability of wind power grid and grid-friendly wind farmconstruction.In this paper, considering the widely used doubly-fed wind generator, the followingstudies were carried out after mastering its working principle and control strategy.①In order to study the impact of parameters and operating states on thesmall-signal stability of doubly-fed wind generator, a small-signal analysis mode of thedoubly-fed wind turbines generation system is established based on its state equations.The small-signal stability was studied by calculating the eigenvalues after changing themechanical parameters, electrical parameters and operating states of doubly-fed windgeneration system. Furthermore, parameter eigenvalues sensitivity under differentoperating conditions was calculated and the influence degree and trend of eigenvalueswere also analyzed by introducing the concept of eigenvalue sensitivity.②A small-signal analysis model considering the change of grid frequency isestablished in order to investigate the influence of grid frequency variation on thestability of doubly-fed wind power generation system. The eigenvalues of improvedmodel and conventional model were calculated and the small-signal stability ofdoubly-fed wind power generation system was analyzed under different grid frequency.Then the validity of model and theoretical analysis were verified by simulation.③In order to improve the capability of doubly-fed wind generator to participatein grid frequency regulation, a frequency integrated control strategy with rotor speedcontrol loop was proposed based on the analysis of existing control strategies combinedwith to regulation characteristics of doubly-fed wind generator. The control principle of different strategies and their simulation results after a grid frequency changing werecompared to verify the effectiveness of the proposed control strategy.The research results can provide a certain reference value for improvingsmall-signal stability of wind power system as well as frequency control regulationparticipation, and lay a theoretical foundation for further improvement to the doubly-fedwind turbines grid adaptability.