Research On Broadband Impedance Modeling And Oscillation Suppression Method Of D-PMSGS Based Wind Farm

In the context of the continuous depletion of fossil energy,in order to achieve green and sustainable energy development and promote the implementation of the national energy strategy of "carbon neutralization and carbon peak",the penetration rate of new energy power generation represented by wind power has increased significantly.As the mainstream model of wind power generation,the installed capacity of D-PMSG is also increasing rapidly.With the continuous expansion of the scale of direct-drive wind power generation,more and more power electronic devices are connected to the power grid,the power electronic characteristics of the power grid are increasingly obvious.Moreover,the power grid intensity is reduced.As a result,when the D-PMSGs based wind farm is connected to the grid,the problem of broadband oscillation is becoming more and more serious,which may cause problems such as disconnection of the wind turbine protection action and equipment damage,which seriously affects the safe and stable operation of the power grid.Therefore,it is urgent to explore the oscillation mechanism of D-PMSGs based wind farm when connected to weak power grid and study the stability control method to suppress oscillation under weak power grid.Therefore,the main innovations of this paper are as follows:(1)Considering the influence of phase-locked loop,current loop and other control links,the positive and negative sequence impedance models of the direct-drive wind turbine and the SVG of D-PMSGs based wind farm in the static coordinate system are established,and the direct-drive wind turbine and SVG are analyzed.The impedance of direct-drive wind turbine and SVG impedance show negative resistance characteristics in the sub / super frequency range,which is prone to oscillation when connected to the weak grid.Based on the established impedance models of direct-drive wind turbine and SVG,considering the transmission line impedance and transformer impedance in D-PMSGs based wind farm,the positive and negative sequence impedance model of direct drive wind farm is constructed.The impedance sweep simulation platform is built to verify the correctness of the impedance model of the DPMSGs based wind farm.(2)Based on the established impedance model of D-PMSGs based wind farm and using the impedance stability method,the mechanism of oscillation problem of DPMSGs based wind farm connected to weak grid is analyzed: the impedance of DPMSGs based wind farm presents negative resistance capacitive characteristics in the middle and low frequency range,and it is easy to oscillate when interacting with weak grid.The influence of control links and operating conditions of D-PMSGs based wind farm on the stability of D-PMSGs based wind farm is analyzed: the stability of DPMSGs based wind farm is mainly dominated by direct-drive wind turbine and SVG.The larger the band width of phase-locked loop and current loop in direct drive fan control system,the more the number of wind turbines in the wind farm,the greater the output power rate and the weaker the strength of connecting to the power grid,the easier it is for direct drive wind farm to lose stability and oscillate.The correctness of the oscillation mechanism analysis of D-PMSGs based wind farm is verified by simulation.(3)Aiming at the oscillation problem when the D-PMSGs based wind farm is connected to the weak grid,an impedance reconstruction control method is proposed to suppress the oscillation problem of the grid connected system of the D-PMSGs based wind farm,based on the oscillation mechanism of the D-PMSGs based wind farm.In this method,the voltage feedforward control of band-pass filter is added to the SVG control system in the wind farm to reconstruct the impedance of the whole wind farm and improve the grid connection stability of the wind farm.The D-PMSGs based wind farm controlled by impedance reconstruction increases the equivalent damping of the system,dissipates the oscillation energy in the system,suppresses the oscillation of the system and increases the stability.Using the impedance stability analysis method,it is concluded that this method can effectively suppress the system oscillation under different control parameters and operating conditions.Finally,the effectiveness of the oscillation control method proposed in this paper is verified by simulation.