Research On Multi-port Energy Router Based On Isolated Dual Active Full Bridge DC/DC Converter

With the progress of science and technology,there is an ever-growing demand for energy in the society.Due to the exhaustion of traditional renewable energy and the pollution of human living environment,it is urgent for sustainable development to gradually improve the utilization rate of renewable energy and reduce the dependence on traditional fossil energy.However,the uncontrollable characteristics of wind energy,solar energy,geothermal energy and other distributed energy have certain fluctuations in the generated electricity.While the user group as a load,it is impossible to adjust the power generation intelligently,which has a negative impact on the operation of the grid.To deal with its problem,foreign experts put forward the idea of developing and popularizing DC microgrid.Because of the non-existent of the problem in AC gird such as reactive power compensation and skin effect,the DC power grid has made a great importance in the society based on AC.At the same time,the development of power electronics technology provides convenience for connecting different energy storage units in DC microgrid and facilitating energy interaction between DC buses of different voltage levels.The concept of energy router has come into being.Based on the application of energy router,this paper studies its basic energy transmission unit,namely Isolated Dual Active Full Bridge DC/DC Converter(DAB).First of all,there is a high-frequency transformers existing in the isolated bi-directional active DC/DC converter topology for electrical isolation and the symmetrical structure realizing bi-directional flow of energy.What’s more reasonable adjustment of control quantity is easy to achieve soft switching and other advantages.Thanks to these advantage,DAB has become the better topology of bi-directional DC/DC converter.In order to further understand the operation mode and system model of the topology,the working principle,power transmission characteristics and soft switching range of DAB under single phase shift control,double phase shift control and extended dual phase shift control are analyzed in detail.On these basis,the operating range of the system is gradually expanded,resulting in different modes of operation.In order to further improve the overall efficiency of the system and reduce device losses,it is necessary to analyze the operating equation of the system and obtain the optimal trajectory.Reflux power is the focus of system optimization.According to the transmission characteristics of its reflux power and the overall loss model,the corresponding optimal control strategy is put forward,and the relevant contradictions are found.What’s more,the experimental platform with DSP as the control core is built to compare the two optimization strategies and verify their effectiveness and feasibility.The energy router used in DC microgrid is mainly responsible for power transmission between different DC buses.Because the parameters of different transmission modules are different,their maximum transmission power is different too.Therefore,two allocation strategies are proposed to allocate the total power required in the energy router to each module: coordinated allocation and variable ratio allocation.Based on the two control strategies,the system model is built in Simulink to simulate and analyze.The corresponding speed and stability of transmission power of each module are observed when the input voltage fluctuates.Then the validity of the two control strategies is verified and the optimal control mode is determined.