Multi-port Energy Router And Its Application In Microgrid

With the increasing demand for energy in human society and the depletion of fossil fuels,the development of renewable energy has become an important means to solve the current energy problem.In recent years,although significant progress has been made in the power generation technology of renewable energy,the grid connection of renewable energy with high penetration rate still brings many adverse effects to the power grid.Microgrid technology,which can realize local consumption and regulation of distributed energy,is an effective way to solve these problems.DC microgrids do not have the problems like synchronization and reactive power flow of distributed power sources and are more efficient and energysaving,so they have been widely concerned.Multi-port energy router is the key equipment of DC microgrid because of its high efficiency,high power density,allowing multiple power supplies and loads to work together and simple control.Therefore,this paper conducts research on the topological structure of multi-port energy routers and control methods and coordinated control strategies for port converters,and the main work includes:(1)A five-port energy router topology is studied for specific application scenarios of energy routers,and corresponding mathematical models are established.Among them,the energy storage port adopts a bidirectional Buck/Boost converter to realize voltage level conversion and bi-directional energy flow.The Buck converter is adopted at the DC load port to realize the conversion of voltage level and supply power for DC load;The three-level DC/DC converter is adopted at the PV unit port to realize the conversion of voltage level.The T-type three-level DC/AC converter is adopted at the power grid port to realize AC/DC conversion and bi-directional flow of electric energy.The AC load port uses a threephase bridge converter to realize AC/DC conversion and supply power for AC loads.(2)According to the function and operation characteristics of each port,the controllers of every port are researched and designed.Among them,the grid-connected port and the AC load port adopt the double closed-loop control method.The DC load port adopts non-singular terminal sliding mode control based on an observer in an extended state.The PV port adopts the conductance increment method to realize maximum power point tracking,and in the island mode,when the battery does not meet the charging and discharging conditions,the double closed-loop control method is adopted to realize voltage stabilization via DC bus.In the gridconnected mode,the energy storage port adopts constant power control,while in the island mode,the virtual DC motor control method is adopted to improve the robustness of the DC bus voltage.(3)Considering the system power balance,DC bus voltage stability and energy storage unit protection,the coordinated control strategy of multi-port energy routers is studied.According to the specific operation scenario of each port,the running state of the energy router is divided into9 working modes,and the corresponding control strategy is proposed to realize the safe,stable and reliable operation of the energy router.(4)According to the previous research results,the DC microgrid experiment platform based on the energy router is built,and the operation characteristics of the energy router are experimentally studied.The feasibility and effectiveness of the proposed structure and its control method are verified by experimental tests on several typical operating modes of the energy router.