Research On Control Strategy Of Microgrid Inverter Based On Power Quality Improvement

Microgrid integrates distributed power sources and makes full use of the advantages of distributed power generation,so that clean energy has been developed and utilized on a large scale.Distributed power supplies power to the grid or load with the help of interface inverters.Due to the weak inertia and small damping characteristics of the microgrid system,its operation status is easily affected by the operating characteristics,control methods and load characteristics of the microgrid,resulting in increasingly prominent power quality problems,making the microgrid system unable to operate safely and reliably.The inverter is an important part of the microgrid system.How to improve the control strategy of the inverter on the basis of the existing system structure to improve the power quality of the microgrid has become a hot spot in the research of new energy power generation systems.In this thesis,the control strategy of microgrid inverter is taken as the research object,aiming at the problems of voltage and frequency deviation and unbalanced power distribution in the operation of microgrid,the virtual synchronous generator control(VSG)is used as the basis of the inverter,and then improved to improve the power quality.In this thesis,the inverter control strategy of microgrid is studied,and Virtual Synchronous Generator(VSG)control is used as the primary control strategy of inverter for the purpose of improving power quality in view of the voltage and frequency deviation and power distribution imbalance problems that occur in microgrid operation.Firstly,this thesis analyzes the basic principle and mathematical model of VSG control.The mathematical model and electromagnetic characteristics of the synchronous generator are analyzed,and the topological structures of the inverter circuit and the synchronous generator are compared,and the corresponding relationship between the two is obtained.By introducing the electromechanical equation of the synchronous generator into the control of the inverter,the second-order mathematical model of the VSG is established,so that the inverter can obtain the ontology characteristics of the synchronous generator.Secondly,a VSG control strategy based on fuzzy secondary control is proposed to solve the problem of voltage and frequency deviation during the operation of microgrid.In this control strategy,VSG control,as the primary control of the microgrid inverter,belongs to differential control,so fuzzy secondary control is added to the control system of the inverter to compensate the voltage and frequency deviation of the system.When the microgrid is operating in an isolated island,it ensures that the voltage and frequency of the system can accurately track the rated value,so that the voltage and frequency meet the requirements of system operation;when the mode is switched,it ensures the synchronization between the microgrid and the public grid,and then the microgrid completes grid connection.Simulink is used to build a simulation model,and the proposed strategy is compared with the traditional VSG strategy and the VSG strategy based on PI secondary control to verify the effectiveness of the proposed method.Finally,in view of the problem that the reactive power cannot be accurately allocated according to the capacity ratio caused by the mismatch of line impedance,the VSG control strategy based on fuzzy secondary control is correspondingly improved,and the adaptive virtual impedance module is introduced to realize the inverter.Precise allocation of reactive power between them.This method analyzes the output power characteristics of the parallel inverter system and the conditions of power balance distribution,and introduces an adaptive virtual impedance module in the VSG control to compensate for the mismatch of line impedance,so as to ensure that there is no connection between the parallel inverters.Functional power can be precisely allocated according to the capacity ratio.At the same time,the voltage drop caused by the adaptive virtual impedance is compensated by the fuzzy secondary control,so as to improve the voltage quality of the PCC point.The simulation is carried out in Matlab/simulink,and the rationality and effectiveness of the method are verified by comparing the simulation results before and after adding the adaptive virtual impedance under different working conditions.This thesis has 53 figures,6 tables,and 81 references.