Study On Control Strategy Of Isolated Dc Microgrid

DC microgrid which connects various distributed generations,energy storage devices,and load through a DC bus and connects to the AC grid through a special interface has gradually become the new direction for future microgrid research in recent years.Compared with AC microgrid,DC microgrid structure is simpler,more flexible,more convenient to control and adapt to growing requirement of DC load.The structure of the isolated DC microgrid is weak.Without the electrical energy support of the distribution network,the inertia and capacity of the system are relatively small,and the voltage of the bus is greatly influenced by the change of power.In this paper,the radial DC microgrid with a single bus,which consists of permanent magnet wind power generations,photovoltaic cell power generations and battery energy storage is studied.According to the stability margin of DC bus voltage and the charge state of battery energy storage,the working states of DC microgrid are divided.The hierarchical control strategy which is suitable for island operation of DC microgrid is presented in this paper,on the basis of analyzing the mathematical models and power output characteristics of each unit in DC microgrid.The hierarchical control strategy of DC microgrid is divided into control strategy of system level and control strategy of converter layer,according to the control requirements of maintaining stability of DC bus voltage in DC microgrid.Then the control methods of wind power generation unit,photovoltaic power generation unit,energy storage unit and load unit are designed.The simulation model of DC microgrid is established on the platform of PSCAD/EMTDC simulation software,and the simulation parameters are set up for simulation analysis.Then we observe the fluctuations of the bus voltage under the three conditions when the output power of the micro-source changes abruptly,the load power changes abruptly,and the two changes simultaneously.When the bus voltage enters the preset voltage range of the control strategy,results which the micro source can change the force size according to the control instruction,the load can be operated according to the control requirements,and the power buffer capacity of the battery can suppress the lack of power in the DC microgrid can be seen from the experimental data.Finally,scientificity and effectiveness of the established model and control strategy are confirmed from the simulation results.