Reseach On Control Strategy Of Doubly-fed Induction Generator To Suppress Electromechanical Oscillation Of Power System

As the proportion of wind power generation in the power system continues to increase,some synchronous generators are being gradually replaced,the system damping is reduced,power electronic equipment is increased,and the structure of the power system becomes more complicated.Moreover,the integration of large-scale wind power at the weak point of the power grid also brings many disadvantages to the electromechanical oscillation phenomenon in the power system.Under this background,it is an important topic to study how to use wind turbine generator to suppress electromechanical oscillation.This paper mainly studies the effects of large-scale wind power access based on double-fed induction generators(DFIG)on electromechanical oscillation in power systems and the suppression of electromechanical oscillation after additional control of wind generators.The main research contents of this paper are as follows:Firstly,this paper studies the working principle and composition of a doubly-fed wind power system,and establishes a dynamic mathematical model of DFIG.The dynamic model established here lays the foundation for the analysis of the response of the DFIG control link to the electromechanical oscillation of the power grid,and the additional damping controller to enable the DFIG to participate in the suppression of electromechanical oscillation.Secondly,taking the two-machine system as an example,the qualitative analysis of the influence of the wind generator on the damping characteristics of the system before and after the integration into the system provides a theoretical basis for adjusting the output of the wind generator to participate in the suppression of electromechanical oscillation.Through time-domain analysis and frequency-domain analysis,the response of different control links on the rotor side of DFIG to electromechanical oscillation in the power system is studied.It is concluded that the active/reactive power control links on the rotor side respond significantly to oscillations.A damping controller is added at the active/reactive power control link to obtain the damping capacity that can be provided after the additional control and the effect on the stability of its own shafting.Finally,for the non-linear and uncertain parameters of the power system with doubly-fed wind power interconnection,it is proposed to introduce fuzzy control theory to design the DFIG additional fuzzy damping controller.The designed controller has strong robustness.In order to reduce the influence of additional control on the stability of the DFIG shaft system,the damping controller is designed to include active-reactive control hybrid modulation.By constructing the objective function and allocating the control ratio of the two channels reasonably,compared with the single active power control or reactive power control,this method takes into account the system damping and the DFIG shaft stability.The simulation models of an interconnected power grid with a large-scale doubly-fed wind farm were built on the MATLAB/Simulink platform.The effectiveness of the controller was verified in the IEEE four-machine two-regional test system and the New England 10-machine 39-bus test system.