Modeling And Characteristics Analysis Of Doubly Fed Induction Generator Based Wind Turbine In Electromechanical Time-scale Based On Amplitude-Phase Motion Equations Method And Its Impact On Power System Stability

With the increasing penetration of wind power in power systems,the impact of the wind turbine generators(WTGs)on the dynamic process of power systems gradually emerges,the feature of power electronics dominating power systems become prominent,and the dynamic stability problem becomes increasingly complex.For the safe and stable operation of power systems,according to the actual conditions of wind power penetration,grid operators have put forward grid code on grid-connection WTGs in stages to require WTGs to bear corresponding responsibilities.The current grid code requires WTGs to have transient control,while the next generation of grid code will require WTGs with inertia control.In the power system under high wind power penetration,electromechanical time-scale dynamic characteristics of WTGs under different control and parameters have gradually become the core factors affecting the electromechanical dynamic process of the system.Therefore,it is of great practical significance and theoretical value to deeply study the dynamic stability of the power system under high wind power penetration.Current researches still mainly rely on mathematical and modular approaches to model WTGs in electromechanical time-scale which can be easily applied to numerical simulation studies or eigenvalue analysis of system stability problems,but lack of physical and general abstractions of the electromechanical time-scale dynamic characteristics of WTGs and hence have insufficient mechanism understanding of the system dynamic process.This paper have taken doubly fed induction generator(DFIG)based wind turbine(WT)with additional inertia control and transient control as study object and physically modeled DFIG-based WT based on the modeling method of amplitude-phase motion equations,and then deeply analyzed and understood small-disturbance characteristics and transient characteristics of DFIG-based WT in the electromechanical time-scale.The dynamic interaction between DFIG-based WT and synchronous generator(SG)is further analyzed,thus deepening the understanding of the impact mechanism of dynamic characteristics of DFIG-based WT in the electromechanical time-scale on small signal stability and transient stability of the power system under high wind power penetration.The main contents are as follows:(1)Different from the current equipment modeling method based on mathematical and modular approaches,the physical and general modeling method based on amplitude-phase motion equations is introduced.And then transient model and small signal model based on amplitude-phase motion equations in the electromechanical time-scale are established for DFIG-based WT with additional inertia control and transient control.(2)Applying the small signal model of DFIG-based WT based on amplitude-phase motion equations,open-loop transfer-function analysis are presented from the perspective of the dynamic relationship between the active power variation excitation and the internal voltage phase response and the dynamic relationship between the reactive power variation excitation and the internal voltage amplitude response,to analyze the small-disturbance characteristics of DFIG-based WT in the electromechanical time-scale.And hence the influence mechanism of inertia control,voltage control and other factors on the inertia characteristic,damping characteristic and the reactive power variation excitation-the internal voltage amplitude response characteristic is deeply understood.(3)An idea about applying the small signal model of DFIG-based WT based on amplitude-phase motion equations and the concepts of self-stabilizing/en-stabilizing property to physically analyze the dynamic interaction between SG and DFIG-based WT is proposed.And then the impact mechanism of the small-disturbance characteristics of DFIG-based WT under changed control parameters in the electromechanical time-scale on low frequency oscillation of SG is explained from the perspective of synchronization /damping power change based on the Bode diagram and the torque analysis method.on transient stability of the power system under the condition of light grid fault are analyzed by applying the transient model of DFIG-based WT based on the amplitude-phase motion equations.The idea about studying transient characteristics of the equipment from the perspective of time-domain response characteristics is proposed,namely regarding the equipment model as a “gray box”,and observing the time domain response of the output side and the time domain response of the state of the internal energy storage components under large disturbances excitation on the input side.According to the deep understanding of the inertia characteristic and the reactive power variation excitation-the internal voltage amplitude response transient characteristic of DFIG-based WT under the condition of light grid fault,the impact mechanism of transient characteristics of DFIG-based WT on the interaction between DFIG-based WT and SG during light fault is analyzed,and hence the influence of transient characteristics of DFIG-based WT on the first-swing stability of SG during light fault is explained.(5)Transient characteristics of DFIG-based WT under transient control and its influence on transient stability of the power system under the condition of deep grid fault are analyzed by applying the transient model of DFIG-based WT based on the amplitude-phase motion equations.From the general perspective of inertia characteristic and the reactive power variation excitation-the internal voltage amplitude response transient characteristic,transient characteristics of DFIG-based WT under transient control are also understood.Besides,the dominant impact factor of transient characteristics of DFIG-based WT on the first-swing stability of SG is analyzed considering the influence of the change in the electrical distance of DFIG-based WT connected to the grid.