Study On Control Strategy Of Virtual Synchronous Generator For Microgrid And Its Parallel System

Due to the continuous reduction of fossil energy and the serious pollution of the environment caused by the use of fossil energy,renewable energy has become the focus of attention,and a microgrid has been born in this context.Although microgrid has many advantages,it lacks inertia and damping compared with large power grid,and is vulnerable to external interference.A virtual synchronous generator(Virtual synchronous generator,VSG)is studied in this paper to simulate the inertia,damping and frequency modulation and voltage regulation of the synchronous generator.Firstly,several common control strategies of traditional microgrid inverters are introduced,and the advantages and disadvantages of each control strategy are pointed out,and then the VSG control strategy is proposed.By analyzing the mathematical model of synchronous generator and the mechanical motion of rotor,the VSG simple model is established.Then the main circuit structure,power-frequency regulation part,virtual excitation regulation part of the in-depth study.Secondly,the influence of the change of electrical parameters(resistance and inductance)on the output power of the inverter and the change of control parameters(moment of inertia and damping coefficient)on the power and frequency of the system are analyzed,and the response control parameters are designed based on the previous analysis.Then the conditions of grid-connected microgrid are analyzed and the pre-synchronous control strategy is designed.a simulation model is built on the MATLAB software platform.Fixed load simulation,load mutation simulation,grid-connected mode simulation and pre-synchronization simulation were carried out under single VSG isolated island operation.The change of moment of inertia and damping coefficient are simulated and compared respectively.The true results are consistent with the previous proposed control theory.Finally,the power allocation problem and power decoupling problem of VSG dual-machine parallel are introduced.In order to solve the power coupling problem,the virtual impedance is first introduced to make the system circuit inductive,and then a power decoupling method is designed to control it.The simulation results verify that this method can not only solve the power coupling problem better,but also improve the output voltage quality of VSG dual-machine parallel system.