Research On Control Strategy Of Energy Storage Inverter Based On Virtual Synchronous Generator

In recent years,with the increasingly prominent energy problem,the application rate of distributed generation（DG）based on renewable energy such as wind energy and photovoltaic is gradually increasing.As the key equipment for distributed energy access to the grid,the application of grid-connected inverters in the power system is also increasing.Compared with the traditional synchronous generator（SG）,the distributed power source integrated into the grid through the inverter has the advantages of fast response speed and flexible control mode,but lacks the inertia and damping characteristics of SG,which affects the power system stability.In order to solve this problem,the virtual synchronous generator（VSG）technology that simulates the external characteristics of SG by establishing the dynamic relationship between energy storage energy and system frequency has emerged.This control technology not only has the droop,damping and inertia characteristics of SG,but also has the advantage of free configuration of parameters,and the effect of improving the stability of the system,and now it has become a current research focus.However,as an emerging technology,virtual synchronous generator technology still has many problems to be solved^[1-3].Based on the above background,this paper mainly studies the control strategy of energy storage inverter based on virtual synchronous generator.First,based on the electrical and mechanical equations of SG,this paper establishes the rotor operating equation and excitation equation of the virtual synchronous generator,and focuses on the selection of the current loop feedback value and the selection of open-loop structure and closed-loop structure of voltage loop of the voltage and current loop,then,the influence of control parameters of virtual synchronous generator on power frequency control is analyzed by using the transfer function of power and frequency under grid connected and off grid conditions,finally,a single machine grid connected system is built for simulation verification,which lays a theoretical foundation for the following control strategy research.Then the photovoltaic and energy storage system based on virtual synchronous generator is realized.For the DC side of the inverter,which is less studied,the focus is on photovoltaic modules and maximum power point tracking（MPPT）and energy storage DC-DC converter control.It also introduces the complementary effect of energy storage system to photovoltaic system,the structure of photovoltaic and energy storage system based on virtual synchronous generator,and a dynamic management strategy based on SOC limitation.Simulation of simunlink verifies the correctness of the above modules and control strategies.Furthermore,on the AC side of the inverter,for the VSG frequency oscillation problem under the power dispatch command,based on the analysis of the system oscillation process,according to the relationship between virtual inertia and angular frequency,angular frequency change rate,an adaptive control strategy of virtual inertia is proposed,and the principle of parameter selection is given.Simulation results show that the proposed control strategy is effective and superior.