Study Of Electromechanical-time Scale Characteristics Of Doubly Fed Induction Generator Type Wind Turbine And Its Impact On Power System Electromechanical Dynamics

With the growing penetration of wind power generation in power system these years,especially in China's north-east and north-west area,the wind power generations have become the major source in power system.To study its impacts on power system dynamic stability have great realistic significance.The dynamic properties of wind power generation are the core factor in determing the power system dynamic behviors,while the controllers in wind power generation dominate its dynamic properties.The typical wind power generation has three kinds of controllers in different time scale.Under different time scale disturbances,the dynamic properties of wind power generation are determined by different time scale controllers.Multi-time scale has become a new characteristic in power system dynamic stability issues.Consequently,the key is in deeply understanding wind power generation.In this paper,we change the traditional modeling method which is based on the mathematical and structural description,and propose the motion equation modeling method which relies on the relation between the magnitude amd phase angle of internal voltage,and input and output power.Based on the motion equation model,we study the electromechanical time scale properties of doubly fed induction generator(DFIG)type wind turbine(WT)and its impacts on power system electromechanical times scale stability.The concrete content is in following:(1)The multi-time scale sequential control in DFIG type WT and the multi-time scale response characteristics of DFIG type WT's internal voltage is introduced.The corresponding relation between multi-time scale dynamics and controllers is illustrated.Then we discuss the relation between power system stability issues and DFIG type WT's multi-time scale dynamics.The connotations and challenge of power system multi-time scale stability after integrating large amount of wind power generation are elaborated.(2)The concept of the motion equation is proposed and then the motion equation of DFIG type WT in electromechanical time scale is obtained.We build the linearized model in electromechanical time scale when considering DFIG type WT in different operation areas,and neglecting the dynamics of DC voltage time scale and AC current time scale.Based on it,we set up the motion equation in reactive power control mode and terminal voltage control mode separately.According to the relation between power and states,we illustrate the physical meaning of motion equation.By comparing with the detailed model in time domain simulation,the effectiveness and veracity of the proposed model for displaying the electromechanical properties of DFIG type WT is validated.(3)The basic properties of the inertia of DFIG type WT are studied.Though the motion equation,the analytical expression of inertia of DFIG type WT is achieved.From it,we study the inertia by considering different phase locked-loop(PLL)parameters and DFIG type WT working in different operation areas,and then propose the method that to enhance the inertia by changing the parameters of PLL.The system frequency dynamic analysis method considering large integration of wind power generation is proposed.By comparing to the detailed electromagnetic transient model in time domain simulation,the effectiveness of the method is validated.The method can be well used to predict and evaluate the dynamics and impacts of different inertia of DFIG typed WT on power system frequency dynamics.The impacts of different inertia characteristics on power system dynmaics are studied,and the principles associated to different inertia characteristics are concluded.(4)The dynamic properties of phase and magnitude of internal voltage of DFIG type WT responding to synchronous generator(SG)'s internal voltage variation,and the physical process and influence path of DFIG type WT's internal voltage on SG's damping are studied.The comparison standard that remains the internal voltage of DFIG type WT unchanged is proposed for evaluating the impact of DFIG type WT on SG's damping.The similarities and differences of DFIG type WT working at reactive power control mode and constant power source are compared.The main impact factor of DFIG type WT working at reactive power control mode on SG's damping is concluded.Based on it,the influence path of the DFIG type WT working at terminal voltage control mode are also studied.(5)The method for improving SG's damping by change PLL's parameters of DFIG type WT is proposed.From the viewpoint of motion equation,the principle of the method is illustrated.From the relation between power and states,we propose that the PLL in DFIG type WT can be seen a natural power system stabilizer(PSS).