Research On Source-storage-load Coordination And Optimal Control Of DC Microgrid With Virtual Energy Storage

With the increasingly serious problems of energy shortage and environmental degradation,the connection of wind power,photovoltaic and other renewable energy power generation to DC microgrid has been widely used all over the world.However,the high penetration of new energy power generation will inevitably reduce the stability of power grid operation.As an important unit of microgrid,energy storage equipment can smooth the power fluctuation of the system caused by climate uncertainty,but it also increases the operation cost of the system.With the rapid development of the power grid,a considerable number of flexible and controllable loads have been integrated into the DC microgrid.Therefore,the source-storage-load with increasing controllability in the DC microgrid needs an efficient coordination method to give full play to its grid connection support potential.In this paper,a mathematical model of a DC microgrid including wind turbines,batteries,supercapacitors and controllable loads is established first,and the equivalent model of each unit in the microgrid and control methods of related converters are introduced and analyzed,which provides a theoretical basis for further research.Then,the energy conversion relationship between the energy contained in the controllable load,the wind turbine and the energy stored in the capacitor is analyzed,and the virtual energy storage models derived from the controllable load and the wind turbine are established respectively.To achieve long-term economic operation of the system,a source-storage-load coordination optimization model based on virtual energy storage is established considering load gains,energy storage losses and wind regulation costs to calculate virtual capacitance values in different periods.After the controllable load and fan are classified into energy storage,the charge and discharge response of the energy storage device can be virtualized,which is convenient to improve the energy management and operation capability of the system.Finally,according to the hierarchical control of the DC bus voltage,the state of charge of the energy storage elements and the input sequence of the virtual energy storage,the operation area of the microgrid is divided,and a coordinated control strategy of the DC microgrid with multi-terminal virtual energy storage is proposed.A typical DC microgrid system is built in Matlab/Simulink,and it is verified that the method can maintain the dynamic stability of the system voltage by comparing and analyzing the simulation results.