DFIG Electromechanical-Electromagnetic Transient Modeling And Stability Analysis At Multiple Time Scales

Doubly-fed wind generator(DFIG),as a widely used land wind turbine type,occupies a large share of the wind power market.The stability of DFIG is closely related to the operating state of electromechanical and electromagnetic systems.DFIG electromechanical-electromagnetic system co-simulation is an important means to comprehensively analyze its system characteristics.However,due to the differences in response time scale between the electromechanical part and the electromagnetic part of DFIG,most of the current DFIG studies only focus on the stability characteristics of its electromechanical system or electromagnetic system,and it is difficult to fully reveal its operational stability characteristics.Therefore,the electromechanical-electromagnetic transient model of DFIG under multi-time scale is established,and its electromechanical and electromagnetic transient stability characteristics are deeply studied.It is helpful to discover the potential stability problems in the actual operation of DFIG,it is of great significance to improve the reliability of DFIG operation.In this paper,GE 3.6MW doubly-fed wind turbine is taken as the research object,and the transient model of DFIG mechanical part is established,including wind speed model,wind turbine model,transmission shaft model and pitch control model.Secondly,based on the SVO(Stator voltage oriented),the electromagnetic transient model of the wind turbine is established,including the transient modeling of the doubly-fed motor,and the control model of the rotor side and the grid side converter.Then combine the two parts of the model to perform time domain co-simulation of DFIG on multiple time scales.Finally,the positive and negative sequence impedance model of the DFIG rotor side is built by harmonic linearization method.The stability of the rotor side converter is analyzed by impedance-based stability analysis method.The impedance characteristic curve of the rotor side converter and the grid are analyzed.The intersection of the impedance characteristic curve finds the potential resonant frequency point and compares it with the simulation results of the time domain simulation to further verify the correctness of the impedance model.The results of joint time domain simulation and impedance model numerical analysis by DFIG electromechanical-electromagnetic transient model show that:the DFIG transient process caused by the disturbance of the electromechanical system generally lasts for a few seconds;when the grid fails,the transient model of DFIG is unstable,and the stator current and rotor current change abruptly,which will greatly affect the stability of DFIG;when the DFIG interacts with the grid,the disturbance of the electromechanical system or the grid may cause instability of the DFIG due to impedance mismatch.