Research On Permanent Magnet Direct Drive Wind Power System Based On Virtual Synchronous Generator

As a representative of clean energy,wind energy has developed rapidly in recent years.As the main utilization method of wind energy,wind power accounts for an increasing proportion in the power system year by year.Wind power generators are mainly integrated into the grid through power electronic devices,and their grid-connected characteristics are quite different from conventional generators.Wind power does not have the inertial support capabilities of traditional power systems,resulting in insufficient inertia response and frequency adjustment capabilities of wind power systems.To solve this problem,this paper takes the permanent magnet direct drive wind power system as the research object,combining two control strategies of virtual synchronous generator and additional control based on frequency change,and proposes a permanent magnet direct drive wind power system based on virtual synchronous generator and virtual inertia control method based on selection function.The main contents are as follows:(1)First,according to the characteristics of the permanent magnet synchronous generator,a mathematical model of the direct-drive permanent magnet wind power generation system is established.Then,the grid-connected control method of wind power generation system is proposed.The method uses the rotor flux oriented control machine-side converter to realize the maximum power point tracking;uses the voltage vector oriented control grid-side converter to realize the DC bus voltage stability.Finally,a simulation analysis is performed under varying wind speeds,and the simulation results verify the effectiveness of the control strategy.(2)The virtual synchronous generator mathematical model of the grid-connected inverter is established based on the working principle of the synchronous generator.Then a virtual governor is designed to simulate the synchronous generator’s speed control system to realize the adjustment of the system frequency by active power;the virtual excitation regulator is designed to simulate the excitation system of the synchronous generator to realize the regulation of reactive power to the system voltage.Finally,the virtual synchronous generator technology is combined with the inertia response characteristics of the synchronous motor,and it is applied to the converter of the permanent magnet synchronous generator.The rotor flux oriented control is used on the machine side converter,and the virtual synchronous control is adopted on the grid side.The simulation results show that this control strategy can provide effective inertial support for the system and improve the stability of the system.(3)On the basis of traditional power system frequency adjustment methods,combined with the frequency adjustment and parameter tuning process of wind turbines,a power generation system model including thermal and wind turbines is established,and the influence of frequency deviation and frequency differentiation on system frequency stability is analyzed.Then,based on the virtual inertia control of the rotor kinetic energy,a virtual synchronous control strategy of the direct-drive permanent magnet wind power system based on the selection function is proposed.Comparative simulation results show that this method can effectively reduce the frequency change speed,increase the lowest point of the frequency,avoid the secondary drop of power,and improve the stability of the system frequency.