Operation Control Strategy Of Grid-connected Virtual Synchronous Generator With Photovoltaic And Energy Storage

With the depletion of fossil energy,the penetration rate of distributed power sources such as photovoltaics connected to the grid through power electronic converters in the power grid continues to increase,resulting in the power grid showing low inertia and low damping characteristics,and traditional control methods are insufficient to support the safety and stability of the power system run.Virtual Synchronous Generator(VSG)technology emerged in this context.By simulating the external characteristics of synchronous generators,distributed power sources can also exhibit inertia and damping characteristics.The traditional VSG control method mainly focuses on the control effect,ignoring the output characteristics of the DC side distributed power supply,and does not fully consider the power support capability during the operation of the system.Therefore,this article conducts an in-depth study on the VSG control strategy of the grid-connected system with photovoltaic and energy storage.Firstly,the mathematical model of the three-phase bridge inverter is established,the control structure of the grid-connected inverter based on VSG technology is analyzed,and the voltage and current double closed-loop bottom control method is studied.The working principle of the synchronous generator is analyzed,and its electromagnetic and mechanical characteristics is simulated.The virtual governor,virtual rotor and virtual exciter of the VSG are modeled,so that the inverter has the same active-frequency and reactive voltage regulation characteristics as the synchronous generator.Secondly,a two-stage photovoltaic storage grid-connected system based on VSG control is built,the equivalent circuit model and control structure model of photovoltaic power generation units and energy storage systems are established,and the DC bus voltage control method is improved by constructing energy storage power commands.Combining the operating status of the DC-side photovoltaic power generation unit and the energy storage system,four operating modes of the grid-connected system with photovoltaic and energy storage are analyzed,and a power coordinated control strategy based on these four operating modes is proposed to realize the power efficiency control.In order to ensure the smooth characteristics of the charging and discharging power of the energy storage system,the energy storage SOC control strategy is proposed.The feasibility of the proposed control strategy is verified by simulation analysis.Finally,a small-signal model of a single-unit grid-connected optical storage VSG is established,and the impact of two key parameters of virtual inertia and virtual damping on system stability and dynamic response performance is analyzed.By analyzing the power angle curve and the angular frequency oscillation curve of the synchronous generator,the relationship between the virtual inertia and virtual damping and the angular frequency change rate and angular frequency deviation is determined.A VSG parameter adaptive control strategy is proposed,combining energy storage SOC state,system stability constraints and dynamic characteristics constraints,the comprehensive value range of VSG key parameters is analyzed.The correctness of the proposed control strategy is verified by simulation analysis.