Study On Power Fluctuation Suppression And Transient Stability Of Isolated Microgrid Based On Virtual Synchronous Generator

Due to the increasingly deteriorating environmental problems and the increasing exhaustion of traditional energy resources,people begin to actively develop and utilize renewable energy resources including solar energy,wind energy and tidal energy to moderate those problems.However,renewable energy generation(REG)cannot be directly paralled in the main power grid due to its characteristics of randomness,volatility and low power quality.In order to solve the problem in REG,the distributed Microgrid as the carrier of REG emerges.In addition,Microgrids have been widely concerned by researchers for its advantages of flexible construction and operation,as well as the ability to adjust power balance and effectively realize power peak cutting and valley filling.However,many problems still need to be overcome in order to realize the large-scale application of integrated distributed REG，among which the main problems are the static stability caused by power fluctuations in Microgrids and the transient stability caused by system failures.Based on Virtual Synchronous Generator(VSG),this paper studies the power fluctuation suppression and transient stability of Microgrid.The main works of this paper are as follows:In this paper,the equivalent mechanical model and electromagnetic model of the VSG are established based on the traditional synchronous generator(SG)model.For islandded Microgrid power fluctuation problem,this paper proposed a novel VSG based method named Imatation Excitation Control(IEC)method.This method equvalent the the VSG to SG from the aspects of physical mechanism,mechanical properties and external characteristics based on the fluctuation problem of active and reactive power small signal model of single machine VSG build.The advantage of the imitation excitation control method is that the mechanical and electrical characteristics and external characteristics of the synchronous generator are fully considered,and the influence of the resistance ratio control of the low-voltage line in the micro grid is fully considered,so that the control effect is more accurate.In addition,the simulated excitation control method adopts the rotating torque to decouple the active and reactive power,preserving the complete information of the system and minimizing the control error.In this paper,the static stability of the system with power fluctuation is analyzed by using a small signal model.Due to the small capacity of Microgrid and the randomness of load and power generation unit,whose operation and exit are frequent,which can easily lead to the transient stability of the system.Based on the IEC method proposed in this paper,the state model of the single-machine and parallel operating VSG system are constructed respectively,and the adaptive impulse controller is designed to effectively eliminate the transient instability of the system caused by external disturbances.At the same time,Lyapunov direct method is applied to prove the effectiveness of the proposed method.Finally,the validity of the proposed method is verified by simulation cases.