| Global environmental problems are becoming increasingly serious and the world energy is facing crisis.Clean renewable energy represented by solar energy and wind energy provides solutions for the above problems.As an important way to access power system,micro grid has become the research direction of many scholars.Among them,DC microgrid can reduce the number of energy conversion,reduce the power loss of microgrid,single control objectives,simple control methods,which is of great significance in improving the power quality and energy utilization rate.The energy storage in DC microgrid plays a key role in balancing power fluctuation and stabilizing bus voltage.Therefore,the research on its control method and charge discharge power has become a hot topic.In order to simplify the structure of DC microgrid,and to facilitate the design and construction,the paper puts forward the operation "nine zone diagram",and studies the operation and control mode of each section in the nine zone diagram.Based on the stable operation,the system studies the multi-terminal flexible DC micro grid structure and modular micro grid structure for reducing the number of converters on the DC feeder.The modular DC micro grid structure based on energy router is designed.According to the effect of micro power supply on the stability of DC bus,the controllable micro power supply of DC microgrid is divided into three categories: superior module,constant voltage module and energy storage module.The same type of micro power supply is transformed into a module connected to DC micro grid from each port of energy router.The mathematical model of converter in each port of energy router is established.The simulation results show that the proposed structure can achieve power balance and feeder voltage stability in three operation modes.In order to satisfy the controllability of power interconnection in DC microgrid system and reduce the frequent charging and discharging of energy storage,the hierarchical control structure of DC microgrid with energy router is designed,which is divided into three layers:energy router layer,system layer and equipment layer.The control objects and tasks of each layer are studied in detail,and the power control scheme of each layer is formulated.The energy router layer controls the power interaction between the microgrid and the superior distribution network.The operation mode of the DC microgrid is divided into island mode,the superior does not participate in the regulation mode,and the superior participates in the regulation mode.The system layer controls the active power in the system,and proposes a modular DC microgrid power voltage partition control strategy based on energy router,that is,nine zone diagram active power control mode.The reference power of each energy storage in the DC microgrid system with multiple energy storage under constant power control is studied by applying the equal micro increment principle.The flow chart of different energy storage control methods and conversion basis of different energy storage control methods in each type of nine area map is designed.The device layer receives the information from the system layer,takes charge of the control parameters of the internal control mode of the converter at each bottom port,studies the control mode of the inner loop and the outer loop,and determines the overall control mode of the modular DC microgrid with energy router.Finally,based on PSCAD / EMTDC simulation environment,aiming at the modular DC microgrid structure based on energy router,the system power interconnection and DC feeder voltage stability in each area of the nine zone diagram under different operation modes are verified.The results show that the designed system structure and overall control strategy meet the requirements of stability,flexibility and reliability. |
