Research On Control Strategy Of Grid Connected Inverter In Microgrid Based On Virtual Synchronous Generator

With the development of the national economy, the contradictions between fossil energy depletion and demand of economy become more and more significant. Distributed Generation(DG), based on renewable energy system, quickly occupied the key to the future location of the Electric Power Research. Grid-connected inverter in microgrid as a link between microgrids and main grid has important influence on the operation of the micro-grid. Grid inverter use the power electronic devices as the main structure, the resulting problems of which, including low output impedance of the system, the lack of inertia, lack of capacity and power distribution networks as well as difficult to transport the existing policy and regulation of the power system.This paper takes the grid-connected inverter in microgrid as research object. By establishment of mathematical modeling, its working principle and characteristics are detailed analyzed. By analyzing the structure of the micro-grid and traditional control strategies of grid-connected inverter, a comparative study of shortcomings of traditional grid inverter control policy is complicated and a simulation of the control strategy of virtual synchronous generator(VSG) machine is established.To overcome the differences between the motor and the power electronics, the establishment of second order synchronous motor mathematical model is done. After establishment of the correspondence between the key parameters of the synchronous motor and the inverter circuit of the mathematical model, this paper find a way to establish a connection between the two contact, so as to provide a theoretical basis for the control strategy and design ideas.Take grid-connected inverter based on virtual synchronous machine overall control strategy into simulation research. First, the synchronous motor speed and excitation controller principle is analyzed, and frequency controller and virtual excitation controller are designed. Then local analog synchronous motor is designed. In order to introduce the magnitude and the phase angle of synchronous motor body characteristics, the introduction of the plural form of resistance of the resistor and synchronous reactance is used.After the completion of the full system simulation model on SIMULINK platform, the study of the system working, under different conditions including dynamic and steady-state, is worked, showing good operating characteristics of the system. With the analysis to verify the role of inertia, and comparison with synchronous motors and droop control simulation, verification of the design external characteristics and control strategies can be proved. The results show that VSG not only could simulate synchronous motor but also to overcome the lack of droop control. Finally, design and build a LCL 3-phase inverter experimental platform and key part of hardware platform are introduced. Preliminary experiments on the hardware platform is tested to prove the effectiveness of the proposed control strategy and feasibility.