Research On Photovoltaic Grid-connected Power Generation System And Control Based On Virtual Synchronous Generator

In recent years,new energy sources such as photovoltaics have been connected to the power grid on a large scale,which has increased the penetration rate in the power grid.However,the new energy power electronic devices contain almost no inertia and damping,which poses challenges to the frequency and voltage stability of the power system.With the advantages of simulating the characteristics of synchronous generators,Virtual Synchronous Generators(VSG)provide new ideas for grid-connected inverters.Photovoltaic Virtual Synchronous Generator(PV-VSG)applies VSG technology to photovoltaic power generation systems,which is of great significance to the development of photovoltaic power generation systems.The existing PV-VSG is equipped with energy storage and transforms the circuit topology of the traditional photovoltaic inverter to realize the VSG characteristics.However,there are few researches on the coordinated control of the energy storage device and the photovoltaic system,and the suppression effect on the photovoltaic wave power is poor.The study also did not consider the dynamic characteristics of the DC side of the photovoltaic system.The in-depth combination of power backup mode,VSG and maximum power tracking has not been explored in power reserve PV-VSG.In view of the above problems,under the support of the following projects: the National Key Research and Development Program of China "Key Technology and Demonstration of Distributed Optical Record Power Cluster Flexible Grid-Integration"(2016YFB0900300)? the National Natural Science Foundation Project of China "Research on Multi-Objective Optimization and Dual Model Grid-Connected Control of Medium-Voltage Three-Level Full-Power PMSG Wind Power Converters"(51677049),this paper studies the control strategies,operating characteristics,grid-connected performance and stability issues of both energy storage and active standby PV-VSG.Firstly,this paper introduces the research background and significance of this topic,and summarizes the topological structure of photovoltaic power generation system and PV-VSG and the research and development status at home and abroad.The basic control strategy of energy storage PV-VSG is explored,and the active standby PV-VSG control method is proposed.Secondly,the control strategy of energy storage PV-VSG is studied in detail.The mathematical model is established for the common DC bus PV-VSG,and the coordinated control strategy of the common DC bus PV-VSG is proposed.It can stabilize photovoltaic power fluctuations and achieve energy coordinated control.In addition,for the problem of poor harmonic suppression of PV-VSG,a grid-connected current control strategy based on improved repetitive control is proposed,which enhances harmonic rejection of the grid and saves costs.Thirdly,by studying the operating characteristics and standby mode of active standby PV-VSG,two active standby control schemes are proposed and compared.In addition,for the scheme 1,the handover is slow,and the maximum power point is not easy to obtain.An improved peer-to-peer power switching scheme based on interpolation fitting is proposed,which can quickly determine the maximum power point and reduce the switching time.The problem is to propose an improved equivalence scheme based on Lagrangian interpolation prediction to achieve power lead control and reduce the influence of control delay.Lastly,for the fixed inertia PV-VSG,the speed is slow in the grid frequency recovery,and the energy is wasted.An adaptive inertial active standby PV-VSG strategy is proposed to accelerate the frequency recovery and save photovoltaic energy.Finally,the experimental platform of distributed photovoltaic and energy storage clusters is built.The hardware and software system structure of the inverter platform is introduced in detail.The related strategies of energy storage and active standby PV-VSG are verified.The experimental results verify the proposed The correctness of the strategy.