Modeling And Stability Analysis Of Wind Power DC-AC Based On Impedance

In recent years,the wind power developed rapidly in China,the interaction between wind power grid-connected inverter and grid affects the stability of power grid and inverter.Wind power is connected through the inverter.With the increasing of the installed capacity of the wind field,a large number of wind power inverters have connected to the grid,the difference between different wind power grid inverter will cause problems of compatibility.The problem that the output impedance of inverter does not match the grid impedance becomes more and more prominent.The equivalent impedances of other inverter in the grid causes new challenges to the stability of individual grid-connected system.The stability of the grid connected inverter becomes a hot topic in the field of power generation,and the stability of the grid connected system is a hot topic.The characteristics of permanent magnet direct drive wind power generators and its full power converters are studied in this paper.A simulation model,based on RT-LAB real-time simulation platform,are established for a 2.5MW direct-drive permanent magnet synchronous wind power generator system.The real-time simulation experiment is carried out,and the maximum power tracking problem is studied.At the same time,the characteristics of grid connected inverter and the causes of instability are studied too.According to the instability phenomenon,the ratio of the impedance of the grid and the output impedance of the grid-connected inverter to satisfy the Nyquist criterion is proposed.The output impedance and grid impedance of the grid-connected inverter are modeled by harmonic linearization method.The influence of grid impedance on the stability of grid-connected system is analyzed by impedance-based analysis method and RT-LAB real-time simulation experiment.Specific work is as follows:1.In order to study the stability of grid-connected systems under large signal conditions,the mathematical models and power and torque models of wind turbine,three phase stationary coordinate system and dq coordinate system are established respectively.The maximum power tracking problem of direct-drive permanent magnet synchronous wind power generator is studied.The real time simulation experiment of PMSG hardware based on RT-LAB is carried out to achieve the expected target.2.The mathematical model of the machine side PWM rectifier is established,and the control of the electromagnetic torque Te is realized by adjusting the q axis current,so that the maximum power point tracking control can be realized.The control of the rotate speed is analyzed.The filter model and the average model of the PWM inverter are studied,and the mathematical model of the grid-connected inverter is established.The RT-LAB full-power converter system simulation model is established,and the real-time simulation experiment is carried out to achieve the expected target.3.In order to study the stability of the networked system with small signal model,the impedance harmonic linear modeling method is studied.The PLL small signal model is established by using the harmonic linearization method.The output impedance model without PLL and with PLL inverter are established,and the simulation analysis was carried out.4.The grid system was studied and the grid impedance model was established.The criterion about the ratio between grid impedance and the output impedance of DC-AC inverter must meet the Nyquist criterion is studied,and the stability of grid-connected inverter is analyzed.In order to cope with the cyclical change of wind power and the impact of large-scale grid-connected power grid,the impedance model with grid voltage feed forward is established.The influence of grid impedance on the system is analyzed by using impedance-based stability analysis method and RT-LAB hardware-in-the-loop simulation experiment.