Research On Photovoltaic Microgrid System Based On Virtual Synchronous Generator

As distributed power sources such as photovoltaic are more and more widely used in power grids,synchronous generators in traditional power generation modes have inertial damping characteristics,while inverters with traditional control methods do not have such characteristics,resulting in the lack of inertia damping characteristics of power grids,and the stable operation of power systems cannot be effectively guaranteed.Virtual Synchronous Generator(VSG)concept in order to better improve the anti-interference ability of the power system is proposed by scholars in the academic world.Under the condition of retaining the original flexibility and speed advantage of the inverter,the system stability and antiinterference ability are enhanced.It has become one of the most popular and concerned research directions in the field of microgrid.In this dissertation,the overall scheme of photovoltaic microgrid system based on virtual synchronous generator is constructed,and the mathematical model of photovoltaic cells is built.In order to make full use of the energy of photovoltaic cells,the output characteristics of photovoltaic cells are analyzed.This paper briefly introduces the traditional Maximum Power Point Tracking(MPPT)method and its advantages and disadvantages.Based on the traditional control tracking speed is slow and the tracking interval is large,an improved perturbation observation method is proposed,and the LCL filter of the system is designed.The paper studies the application and improvement of virtual synchronous generator technology in photovoltaic microgrid system and analyzes the control structure of virtual synchronous generator in detail.In order to analyze the influence of key parameters on the virtual synchronous generator,a VSG single parallel network small signal model is established.In view of the traditional adaptive control strategy of moment of inertia can not effectively suppress the system oscillation,a VSG multi-parameter collaborative adaptive control strategy is proposed.To solve the problem of offline switching of virtual synchronous generators,a seamless switching and off-grid control strategy based on SRF-PLL is adopted to realize seamless smooth switching of virtual synchronous generators,thus reducing the impact of transient current on microgrid.A simulation model of photovoltaic microgrid system based on virtual synchronous generator was constructed to verify the dynamic performance of the improved perturbation observation method.The proposed control strategy is applied to the photovoltaic microgrid system and compared with the conventional VSG control strategy and the traditional VSG adaptive moment of inertia control strategy.The results show that the proposed control strategy has the best stability and anti interference effect in the face of external load disturbance in the steady-state condition and the transient condition,which is conducive to the stability of the system.The seamless switching control strategy based on SRF-PLL is verified,and the results show that the off-grid mode switching can be smoothly implemented without impacting the microgrid system.The hardware part of the experimental platform and the code generation part of the corresponding design,and the built experimental platform off-grid and grid experimental verification,through the experiment to verify the rationality of the experimental platform design in this paper.