Study On The Control Strategy Of Inverter Based On Virtual Synchronous Generator

Microgrid makes large numbers of distributed energy connected to the grid with minimum impact,which increases the efficiency of distributed generation.However,the lack of inertial support and damping causes great influence on stability of the power system.As for this problem,the virtual synchronous generator(VSG)control strategy is applied to inverter to increase the system inertia by simulating the characteristics of synchronous generators.Generally,microgrid can work on islanded and grid-tied mode.Besides,its system performance will be affected by problems of transform from islanded to grid-tied mode and grid-connected power quality.VSG system in microgrid is taken as the research object in this thesis.The mathematical model of synchronous generator is established.Then according to the model of synchronous generator,the principle of VSG control is analyzed and concrete algorithm is obtained.Besides,modeling of three-phase inverter system is established and parameters of voltage and current double closed-loop control are designed.Based on established dynamic model of VSG,the effect of VSG control parameters on stability and dynamic performance of system is analyzed by root locus method.Besides,control parameters of VSG are designed.The correctness of VSG parameters designed is verified by simulation.In order to realize seamless transform from islanded to grid-tied mode,the principle of presynchronization technology is described in detail and an improved presynchronization control method is studied.Besides,the difference between traditional and improved methods is compared to verify advantages of the improved method.In order to suppress gird-connected current harmonics of VSG,the output impedance model of VSG is established.Then according to output impedance model,the reason that grid voltage harmonics can affect the quality of grid-connected current is analyzed.As for the prolem,a current-harmonic compensation method is studied based on the PMR controller.Besides,a notch filter is applied to current-harmonic compensation in order to eliminate the effect on the fundamental component.By the control method,gird-connected current harmonics are suppressed obviously.Finally,main circuit parameters of experimental platform are designed and experiments of VSG system are completed.The correctness and effectiveness of VSG parameters designing,presynchronization control method,current-harmonic compensation control based on PMR is verified by experimental results.