Research Of VSG Based Integrated Control Method For Transient Stability Of Microgrid

Microgrids can fully utilize the advantages of distributed generation(DG)and make up for its shortcomings,so it has been rapidly developed and widely used.The structure is complex and changeable.The control method is flexible,and it can operate independently or connected to the power network,so the control strategy of the inverter is highly required.Virtual synchronous generator(VSG)control has the characteristics of inertia and damping that traditional inverter control strategies do not have,which can better improve the stability and dynamic performance of the system,so VSG has become one of the research hotspots in recent years.Although the microgrid which based on VSG has good stability,there is still some problem of transient stability in operation,which causes the security risks.In this paper,the transient stability control of the microgrid based on VSG in terms of mode switching and load disturbance is deeply analyzed and studied.The main research contents are as follows:(1)Transient stability control of mode switching in microgrid based on VSGThe transient stability of the VSG when switching between the two operating modes is analyzed.It is found that there is less fluctuation during the process of switching from the grid-connected mode to the island mode,and the switching can be completed naturally.It will occur transient oscillation problem caused by different amplitude and phase of the voltage between microgrid and power network when switching from the island mode to the grid-connected mode.A pre-synchronization control strategy based on coordinate transformation is proposed and the corresponding pre-synchronization controller is designed to make the amplitude,phase and frequency of the voltage consistent with the grid before incorporation with power network.The simulation model is built in the simulation platform of MATLAB/Simulink,and the effectiveness of the proposed pre-synchronization control strategy is verified.(2)Integrated transient stability control of frequency of island microgrid under load disturbanceThe microgrid based on VSG has the problem that frequency may be serious or even exceed the limit during load disturbance.A control method combining VSG control with improved droop control is proposed,and a function to meet the corresponding improved droop control conditions is designed.At the same time,a comprehensive switching control strategy is proposed to ensure the frequency stability of the microgrid,which can keep the frequency safe and stable under differentload disturbances.Aiming at the problem that voltage distortion may be caused when the control methods switching,a voltage synchronization control method is further designed to enable smooth switching between the two control methods and ensure the stable operation of the microgrid.Finally,the effectiveness of the proposed control strategy is verified by simulation experiments.