Research On Energy Management For DC Micro-grid

In recent years, the DC micro-grid becomes more and more popular for its lessenergy connection, higher efficiency and easier to control. The micro-grid has a largenumber of micro-powers with different characteristics, so the micro-power control issignificant in the net system. The power management is not only for the improvement ofpower quality, but also the economic benefit, which also offer great significance to theenergy and environmental crisis.A DC micro-grid system which is composed of photovoltaic cells, batteries andsupercapacitor has been researched. The output characteristics of photovoltaic cells isanalyzed in detail, hysteresis loop control is applied to achieve seamless transitionbetween MPPT mode and the constant current mode in this paper, which strengthened thereliability of the system. Considering the battery features and the interface convertercharacteristics, a effective management strategy is adopted in this paper, which achieves atwo-way flow of energy only with a control circuit and greatly extending the battery life.In addition, combined with the working principle of the supercapacitor and the role in thesystem, this paper adopted a double hysteresis control strategy, which not only avoid thesuper capacitors cut in and cut out frequently, but also achieve the full use of therenewable energy.The bus voltage is the only indicator which denotes power balance in the DCmicro-grid system. In order to ensure the stability of the bus voltage, it needs to managethe three sources. the energy management strategy is given: according to the relationshipof the bus voltage and the three power status, the interface converters were made to workin the appropriate modes. All of the eight possible conditions during the system running islist and the specific mode for each converter is showed in this paper, simulation usingMATLAB software is carried out, to verify the feasibility of the strategy.Finally, the parameter of the main circuit and control circuit is designed in this paper,the experimental platforms are built up, the MPPT experiments, the battery charge anddischarge experiments and the hysteresis experiments of the supercapacitor are carried out to verify the correctness of the theory.