Study On The Control Strategy Of Inverter In Microgrid Based On Virtual Synchronous Generator

As an effective way to integrate various distributed generation(DG),microgrid has become a research focus and hotspot in the field of distributed generation.However,the micro source response is fast and the external characteristic is hard,resulting in the system is prone to oscillations and low stability.Virtual Synchronous Generator(VSG)control technology,as a method to simulate synchronous generator characteristics,can bring about the inherent rotational inertia characteristics of a synchronous generator for a microgrid system,it is of great significance to solve the lack of microgrid system inertia and improve the stability of microgrid system.In this thesis,on the basis of summarizing the control strategy of microgrid inverter,around the VSG control problem of micro source inverter.Firstly,the voltage control structure of the micro source inverter is analyzed in detail,the basic principle of voltage control of inverter SVPWM is given,the voltage current double loop decoupling controller and filter are designed.Secondly,On the basis of analyzing the control structure of synchronous generator,the control system structure of the virtual synchronous generator is given;by analyzing the frequency modulation principle of the synchronous generator,the power frequency controller of the VSG control is designed;by analyzing the voltage regulation principle of the synchronous generator,the excitation controller of the VSG control is designed.Finally,for the frequency regulation problem in transient response of VSG,the relationship between virtual inertia and virtual rotor angular frequency rate is deeply analyzed,based on the characteristics of flexible virtual inertia,a virtual synchronous generator control strategy is proposed,the virtual inertia is adjusted adaptively with the changing rate of rotor angle frequency,and the effects of adaptive parameters on the virtual moment of inertia are also analyzed,and the power frequency controller of the virtual synchronous generator is redesigned.The simulation model of VSG control strategy and the simulation model of adaptive virtual inertia control strategy are set up in MATLAB/Simulink,by comparing the simulation results of VSG strategy with traditional droop control strategy,it shows that the designed VSG not only simulates the droop characteristics of synchronous generators,but also simulates therotational inertia characteristics of synchronous generators.By comparing the adaptive virtual inertia and the traditional fixed inertia VSG control,the simulation results show that the VSG control strategy of the adaptive virtual inertia is realized in real time based on the change of rotor angular frequency,and solves the problem of slow recovery of frequency in transient response of VSG.