Research On Power Balance Of Interlinking Converter In Campus PV Storage Hybrid Microgrid

As a new type of green power supporting system,the campus optical storage hybrid microgrid integrates distributed photovoltaic power generation units,energy storage systems,bidirectional converters,system loads and protection devices to achieve safe,stable and economical operation.The research object of this thesis is the bidirectional converter connected to the AC / DC bus in the campus hybrid microgrid.Under the premise of ensuring the stability of DC bus voltage,AC voltage and frequency,the bidirectional converter mainly realizes the following functions : 1)The bidirectional converter automatically switches the working mode and determines the transmission power according to the system power level;2)The bidirectional converter achieves unit power factor operation;3)The bidirectional converter and the distributed microsource in the microgrid system work in coordination to maintain the system power balance.The specific research contents are as follows :(1)Firstly,this chapter introduces the background and significance of the research topic,and then introduces the research status of the hybrid microgrid,bidirectional converter topology and its control strategy.According to the research background,the topology of optical storage microgrid and bidirectional converter is determined.(2)According to the optical storage microgrid model in this thesis,after determining the topology of the three-phase voltage bidirectional converter,the mathematical models in two coordinate systems are established respectively.Then,based on this model,the working principle and operation mode of the bidirectional converter are analyzed in detail,which lays a foundation for the design of the controller of the bidirectional converter below.Finally,the limitations of the traditional double droop control strategy are analyzed,which leads to the following research content.(3)The bidirectional converter adopts the traditional double droop control,and its control algorithm design process is studied.Aiming at some limitations of traditional double droop control,the corresponding solutions are designed : 1)Introducing power closed-loop control on the basis of traditional double droop control;2)The recovery control is designed for the problem of DC bus voltage fluctuation caused by environmental factors and load switching.3)The action threshold is designed for the problem of frequent switching of converter working mode.Then the specific design method of power current double loop and the setting method of PI regulator parameters are deduced in detail.Finally,a bidirectional converter simulation model is built in MATLAB / Simulink to verify the feasibility of the research strategy.(4)In order to verify the control strategy of the bidirectional converter studied above,a 5KW physical simulation platform is designed and built according to the simulation model.The experimental prototype includes hardware main circuit design,hardware control circuit design and software design.Finally,the stable operation of the bidirectional converter inverter and rectifier state is completed.(5)Aiming at the typical operating conditions of the campus optical storage microgrid,the underlying control strategies of each micro-source in the system are designed respectively,and the system-level simulation model of the optical storage microgrid is built.The simulation results show that the working mode of the bidirectional converter can be changed according to the photovoltaic output level,the state of charge and load of the energy storage unit in the microgrid system,so as to verify the effectiveness of the power coordinated control strategy of the microgrid system.