Research On Economic Operation And Cooperative Control Of DC Microgrid With Virtual Energy Storage

In order to deal with the worldwide energy crisis and environmental degradation,distributed power sources such as wind turbines and photovoltaic power sources have been rapidly developed in microgrids.Photovoltaic and wind power are greatly affected by environmental factors,and their output is volatile.Their high penetration into the traditional power grid will affect the stable operation of the power grid.The energy storage device can adjust the power change,which is often used to suppress the power fluctuation caused by distributed generation and stabilize the bus voltage.However,the investment of traditional energy storage device is bound to reduce the system operation economy.The power of controllable load can be adjusted.As the demand side response equipment,it has become one of the measures to ensure the power grid operation by changing the controllable load power to respond to the power supply.In this paper,the power regulation ability of controllable load is deeply analyzed,and it is regarded as a virtual energy storage device to enhance the power regulation ability of the system.The main research results are as follows:Firstly,the DC microgrid model including wind turbine,energy storage device and load is established.The equivalent model and control strategy of wind turbine,storage battery and super capacitor are introduced.The control strategy of controllable load is analyzed emphatically.Through the control of load,the speed of asynchronous motor of controllable load is changed to realize the regulation of load power.Secondly,considering the speed regulation process of asynchronous motor rotor and the charging and discharging process of super capacitor,the relationship between them is established.The definition of virtual energy storage from controllable load is elaborated,and the expressions of virtual capacitance value and virtual state of charge are derived to characterize the storage capacity of virtual energy storage.Thirdly,considering the water yield of seawater desalination controllable load and the life loss caused by battery balance power fluctuation,the relationship between the virtual capacitance value and the system income is analyzed,and the economic evaluation model of DC microgrid is established.The particle swarm optimization algorithm(PSO)is used to solve the economic model,and the virtual capacitance values corresponding to the optimal system revenue in different periods are calculated to ensure the long-term economic operation of the system.Fourthly,based on the voltage of DC bus and the state of charge of energy storage device,a DC microgrid hierarchical and partitioned control technology with virtual energy storage is proposed to improve the short-term voltage dynamic stability of the system.Finally,a typical example is tested in the RT-LAB hardware in the loop digital simulation platform to verify that under the coordinated control of load and storage,the DC microgrid integrated with virtual energy storage not only has economic operation potential,but also can significantly improve the dynamic stability of the system.