Research On Strategy Of Smoothing Voltage Fluctuation With Hybrid Energy Storage In DC Microgrid

With the increasingly severe problems such as the depletion of fossil energy and environmental pollution,renewable energy,represented by solar and wind energy,has become a new type of power that can be studied and developed for a long time,and the emergence of microgrid has solved the problem of the proximity of new renewable energy sources and the distribution of distributed grids.In recent years,the continuous increase of DC load on the side of the distribution network and the increase of DC power supply such as photovoltaic power generation and wind power generation have promoted the research and development of DC microgrids.With regard to the imbalance of bus voltage and energy flow in DC distribution network,the energy storage unit with dynamic adjustable power flow can be adjusted effectively according to the operation condition of DC microgrid.In this paper,we analyze the shortcomings of the traditional two-way DCs/DC converter in the energy transfer quantity,the adaptability of wide range voltage input and the safety and reliability of operation,which can not meet the needs of the rapidly developing DC distribution network.Therefore,this paper takes the new dual-active full-bridge DCS/DC converter as the research object,analyzes its working principle and applies it to the DC microgrid energy storage unit.In this paper,the operation characteristics and control strategy of DC Microgrid system are introduced firstly,the working characteristics and control modes of photovoltaic power generation unit and energy storage unit are analyzed,and its mathematical modeling is carried out,and its working characteristics are studied by MATLAB simulation platform.Secondly,this paper analyzes the working principle and characteristics of the traditional bidirectional DC/DC converter of energy storage unit,and in view of its limitation,puts forward the use of dual active full-bridge DCs/DC(dual-active-bridge,DAB)converter in energy storage unit,by analyzing the topology of DAB converter,The principle of energy conversion and the working state under the single phase shift control mode,the mathematical model of single phase shift control DAB Converter is created.Aiming at the problem of power reflux and soft switch control in single phase shift control,a small signal model of DAB converter under single phase shift control and double phase shift control is established by means of state space averaging method,and a control strategy of energy storage unit converter based on double phase shift control is proposed.The operation characteristics of the two control strategies are simulated and analyzed by suing MTALAB.Then,in order to realize the efficiency of the energy storage unit,the Energy storage unit converter with dual phase shift control can give full play to the performance of the reservoir,by analyzing the working characteristics of the super capacitor and the battery in the mixed energy storage,coordinating the characteristics of the two work,and combining with the power reflux phenomenon in the work of the energy storage unit DAB Converter,A hybrid energy management strategy based on dual phase shift control DAB Converter is proposed,which enables it to achieve the goal of deflating DC bus voltage fluctuation.Finally,the simulation model of DC Microgrid based on dual phase shift control is set up by using MATLAB simulation platform,and the simulation results are carried out to verify the feasibility and rationality of stable voltage and energy management of energy storage unit converter based on dual phase shift control in DC microgrid.