Research On Parallel Energy Storage Units Control And Energy Management Technology In DC Micro-grid

Under pressure of energy cris is, and the problem of environment protection,the research on micro-grid technology ga ins increasing extensive attention andapplication for all over the world. DC micro-grid, as a self-management region gridform of combined renewable energy system, energy storage system and load, caneither operation in grid-connected mode or island mode. Owing to the phase andfrequency detection like AC grid is not needed, the reliability and controllability aregreatly improved. Thus it is more suitable for dc power supply to access micro-grid.This paper researches each subsystem’s electric power control technique such asphotovoltaic generation and energy storage system, analyzing the control strategiesof DC micro-grid and energy manage ment for the goal to achieve coordinate control.The research on method of equalization control of batteries in parallel is included inthe paper. The main contents are as follows:Propose the micro-grid structure with integrated control objectives, usingwhole control strategy which include center controller and the coordinate control,realize the stable operation of the DC micro-grid. The models and the outputcharacteristics of photovolta ic generation subsystem are analyzed, on the basis ofanalysis the traditional maximum power point tracking control algorithm, proposingvariable step MPPT control strategy, and simulate the switch between differentworking modes.To cope with the current installed capacity of renewable energy, there is anincreasing demand for energy storage system capacity and other issues, in order tomeet the growing demand for energy storage, research the method of equalizationcontrol of batteries in parallel, introducing average current control method andexternal characteristic droop control method, aimed at increasing energy storagesystem capacity, meanwhile realize the balance between parallel battery systemoutput. Designing two stage type charging strategies based on the chargingcharacteristics of the energy storage system, through energy storage system absorbor release power to maintaining the power balance of micro-grid.Combine the micro-grid structure with integrated control objectives, on thebasis of stable DC bus voltage, according to the different energy supply and demandstatus between photovolta ic generation and load, propose energy managementcontrol strategy of DC micro-grid, according to the photovolta ic and the state of thebattery, control the battery energy storage system and photovoltaic systemcoordination work in the corresponding mode, stable the dc bus voltage, ma intain energy supply and demand balance when light or load change, achieving the DCmicro-grid operation stability and efficiently.Under the environment of Matlab/Simulink, establish the simulation model ofDC micro-grid system for PV maximum power point tracking and battery chargingand discharging mode switchover in different working states. And build the smallpower DC micro-grid experiment platform. The corresponding experimental resultsvalidate the feasibilit y and effectiveness of research of the control techno logy of theDC micro-grid.