| With the rapid development of wind power,the high proportion of wind power connected to the power system has led to a major change in the structure of power supply.Wind power has become one of the main power sources in the power system,which has brought great challenges to the dynamic process and stability of power system.In order to deal with the problems of reduced inertia,dynamic deterioration of system frequency and reduced stability caused by the traditional vector control of wind turbine,the wind turbine based on virtual synchronous control,which does not rely on the phase-locked loop to achieve synchronous operation with the grid,is widely concerned and applied by academia and industry.Under this background,the dynamic characteristics of wind turbines with virtual synchronous control(VSyn C)will gradually become the key factor affecting the dynamic process of the system.Therefore,it is of great significance and value to study the dynamic characteristics of wind turbines with VSyn C and its impact on the dynamics of the system.In this paper,the doubly fed induction generator(DFIG)based wind turbines(WTs)with VSyn C is taken as the research object.Aiming at the electromechanical time scale,this paper focuses on the modeling and characteristic analysis of DFIG-based WTs with VSyn C and its influence on the dynamics of power system.The inertia characteristics of DFIG-based WTs with VSyn C and its influence on the frequency dynamic process of the power system,as well as the small disturbance characteristics and its influence on the low frequency oscillation of the synchronous generator(SG)are analyzed and studied.The details are as follows:Firstly,this paper introduces the basic principle and control strategy of DFIG-based WTs with VSyn C.The frequency and amplitude of the internal voltage of DFIG-based WTs with VSyn C are adjusted by the unbalanced active power and reactive power respectively.Using this internal voltage frequency-amplitude control method which is similar to synchronous machine,the frequency of the internal voltage is independent of the grid voltage,and has the characteristics of active response to grid disturbance and self synchronization.Then,based on the concept of motion equation,considering the different operation areas,the motion equation model of DFIG-based WTs with VSyn C in the electromechanical scale is established,and the equivalent inertia and damping coefficient are defined to represent the frequency dynamics of the internal voltage.In Matlab / Simulink,the simulation results of the detailed electromagnetic transient model and the motion equation model in different operation areas are compared to verify the correctness of modeling.Next,according to the expression of equivalent inertia obtained from the motion equation,its physical meaning is explained,and the inertia characteristics of the DFIG-based WTs with VSyn C with different control parameters and in different operation areas are analyzed.On this basis,the dynamic frequency analysis model of power system with DFIG-based WTs with VSyn C is established.By comparing with the detailed electromagnetic transient model,the effectiveness of the proposed method is verified,and the influence of different inertia characteristics of DFIG-based WTs with VSyn C on the dynamic process of system frequency is analyzed and summarized.Finally,the small disturbance characteristics of DFIG-based WTs with VSyn C are analyzed based on the motion equation model.The interaction path and physical process between DFIG-based WTs with VSyn C and the SG,especially the action path of DFIG-based WTs with VSyn C to the damping of the SG,are studied by establishing the model of the SG,DFIG-based WT with VSyn C and the infinite grid system.On this basis,based on the torque method,the influence mechanism of different small disturbance characteristics of the DFIGbased WTs with VSyn C on the damping and oscillation mode of the low-frequency oscillation of the SG is explained. |
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