Research On Control Technology Of Virtual Synchronous Generator For Microgrid Inverter

With the increasing energy crisis and environmental pollution,distributed generation based on clean energy is gradually emerging.As an effective carrier for integrating distributed generation,microgrid has a broad development prospect in improving energy utilization and reducing the impact on the stability of large power grid.However,a large number of distributed generators with inverter as the interface are connected to the microgrid,which will cause the power quality and stability of the system to be affected due to the lack of inertia and damping characteristics of the inverter,so the control technology used by the inverter directly affects the safe and stable operation of the microgrid.Traditional inverter control technologies such as PQ control,V/f control and droop control have been unable to meet the operation requirements of microgrid.Therefore,some scholars proposed a virtual synchronous generator control technology which can simulate the inertia and damping characteristics of synchronous generator.The main research contents of this thesis are as follows:(1)The domestic and foreign references are analyzed,the background,definition,and characteristics of microgrid are outlined,several common control strategies for microgrid inverter are elaborated,and the research status of VSG control technology is mainly introduced.(2)The basic principle of the inverter based on VSG control is elaborated in detail,and the main circuit topology and control system structure of inverter based on VSG control are introduced,mainly including: power frequency controller,excitation controller and voltage current double closed-loop control.The superiority of VSG control technology is verified through the simulation comparison between VSG control and droop control.(3)The equivalent circuit model of VSG parallel system is established to analyze the output power characteristics,and the power equations and control strategies corresponding to different line impedances are introduced.Based on the analysis of the working mechanism of realizing the proportional power sharing,the corresponding parameter matching method is proposed,and the simulation model of two VSGs in parallel is built on the Matlab/Simulink platform to verify the feasibility and effectiveness of the proposed method.(4)By analyzing the limitation of the frequency regulation ability for traditional VSG control,a secondary frequency modulation scheme for VSG control is proposed.Based on this,the effects of the moment of inertia and damping on frequency response are analyzed in detail,and the inertia and damping collaborative adaptive adjustment strategy is designed in combination with the research of the moment of inertia adaptive adjustment.The effectiveness of the inertia and damping collaborative adaptive adjustment strategy is verified by comparing the simulation experiment with the strategy of constant inertia control and the moment of inertia adaptive adjustment.