| Energy is an important driving force for social development.With the development of renewable energy represented by solar energy and wind energy,the penetration rate of distributed generator and micro-grid in the distribution network is increasing year by year,and the inertia of the power system is reduced,which affects the stability of the power grid.As an interface and link between distributed generator or micro-grid and the grid,the inverter plays a vital role in maintaining system stability.Therefore,it is necessary to study inverter control to cope with the above problems.This paper mainly studies the virtual synchronous generator control of micro-grid inverter.Firstly,the research background and significance of the subject are introduced,and the common control strategies of the inverter are introduced.It shows the advantages of VSG in enhancing inertia.The mathematical model and basic working principle of VSG are introduced.The effects of rotor inertia and damping coefficient on the power-frequency characteristics of VSG in island and gird-connected mode are analyzed.A smallsignal model is established and stability analysis is carried out,and a method for accurately and quickly obtaining control parameters is presented.The simulation realizes the stable operation of the VSG under island and gird-connected mode,and has the characteristics of inertia and droop,which indicates the correctness of the theory.Secondly,the coordinated control strategy of PV generation system with energy storage devices based on VSG is studied,and the control principle of photovoltaic and storage battery is introduced.According to the power balance relationship between photovoltaic,energy storage,DC bus and grid-connected inverter,energy management is carried out,and the energy storage battery is used to supplement the photovoltaic to provide inertial support for the VSG.The VSG adjusts the power output according to the battery SOC to perform limit protection.A quantitative analysis of the energy storage equipment required for VSG operation is performed.The simulation has verified the above control method.Thirdly,aimed to the grid-connected switching problem faced by the VSG,the virtual synchronous generator is improved for grid-connected presynchronization.The active loop adds integral control to realize secondary frequency modulation,and uses the root locus and the Bode diagram to improve the stability analysis.The reactive loop introduces voltage feedback correction to achieve secondary voltage regulation.The phase angle uses voltage orientation vector technology for phase tracking.In order to optimize the frequency and active power response,according to the VSG power angle characteristic curve,the relationship between the rotor inertia and the frequency change is analyzed,and a VSG adaptive rotor inertia control method is proposed.The simulation verifies the correctness of the proposed method.Finally,the VSG hardware experimental platform with DSP320F2812 as the control core is built,including the design of the main circuit and the control system of sampling,conditioning,protection,drive,etc.The program is written and debugged on the software CCS3.3 including main program and subprogram of interrupt program,AD sampling,timer interrupt.Based on this,the inverter control is completed to complete the VSG experimental study.The result proves the correctness of the proposed control. |
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