Research On Virtual Synchronous Generator Control Technology Of Microgrid Inverter

With the development of new energy,the application of the microgrid is more and more extensive,which is an important way for distributed generators to access to the grid.As the core of the microgrid,the microgrid inverter is the interface between the microgrid and the grid.The lack of inertia and damping support in power electronics,which makes the microgrid unsafe and unstable.In this context,The Virtual Synchronous Generator(VSG)control strategy is proposed.By simulating the inertia and frequency/voltage regulation characteristics of the traditional synchronous generator,the voltage and frequency support capabilities of the microgrid are increased.The VSG control strategy of a three-phase voltage source inverter is taken as the research object of this thesis.Firstly,based on the analysis of the traditional synchronous generator model,the control principle and ontology algorithm of VSG is given,the dynamic phasors model of VSG is introduced,the influence of parameters on the stability and dynamic performance of the system is analyzed qualitatively,and the related parameters of VSG is designed.The mathematical model of the three-phase inverter is established,the low-level control of VSG is designed.the feasible region of the relevant parameter value is determined by the root locus method.Simulation results show that the design of parameters is correct.Secondly,for solving the coupling problem between the active and reactive power of the VSG,the small-signal model of VSG is established and the mechanism of the power coupling is analyzed.A decoupling strategy based on the diagonal decoupling matrix is introduced to achieve the static decoupling of the VSG power.In order to solve the problem that the performance of the diagonal matrix decoupling strategy is affected by the grid running state,an optimization method based on power angle estimation is proposed,and the effectiveness of the related control strategy is verified by simulation.Thirdly,the research on VSG operation control mainly focuses on two points: control strategy of the VSG seamless transferring from islanded to grid-connected mode and control strategy of multi-function VSG.In the research of the seamless transfer technology,a variable coefficient pre-synchronization strategy based on virtual power is introduced,which greatly simplifies the pre-synchronization process.In the research on control of multi-function VSG,a harmonic detection method based on half cycle and sliding-window iterative algorithm of discrete fourier transform(DFT)is introduced,which combined with fast repetitive control technology can be used to realize compensate harmonic of local nonlinear loads.By using the multi-function VSG strategy,the purpose of expanding the function of VSG and improving the adaptability of VSG.Both of the control strategies are verified by simulation.Finally,the VSG experiment platform is designed and built.Then,the control strategy of VSG,the control strategy of seamless transfer,the harmonic detection method,and the control strategy of multi-function VSG are verified by the experiments.