| The increase in the penetration rate of new energy has brought severe challenges to the safe and stable operation of the power grid.The traditional AC power grid has many commutation links and complex reactive power control,which is not conducive to the consumption of new energy.Compared with the AC grid,the DC distribution network does not need to consider the balance of internal reactive power,and is not affected by frequency changes.When connected to distributed power sources,it can reduce the conversion link,so it can simplify the control and is more conducive to innovation.Energy access and stable operation.Based on the droop control method,the application of flywheel energy storage system in DC distribution network is studied.An improved variable droop coefficient control method is used to optimize the control strategy,thereby increasing the virtual inertia of the system and reducing the DC bus voltage fluctuation.First,the DC distribution network with photovoltaic systems as distributed power generation units is discussed.Mathematical models of flywheel energy storage system,photovoltaic power generation system,grid-connected converter and direct AC load are established,and the topology,control strategy and operating characteristics of each unit converter are analyzed based on the mathematical model.Pave the way for subsequent analysis.Secondly,analyze the collaborative control strategy based on droop control,and study the droop control strategy of flywheel energy storage system in DC distribution network.When load fluctuates,flywheel energy storage and grid-connected converter share power fluctuations.At the same time,the virtual inertia of the DC distribution network is derived,and the relationship between the size of the virtual capacitor on the DC side of the DC distribution network and the change value of the converter output power is established.And by deriving the relationship between the speed of the flywheel energy storage system and the virtual inertia of the system,the theory verifies the feasibility of the flywheel energy storage system to provide inertial support for the system.It lays the foundation for the research of the follow-up improved variable droop coefficient control method.Then,when the load changes,the low inertia of the DC distribution network causes the large fluctuation of the DC bus voltage.Establish the relationship between the rate of change of the DC voltage and the output power of the converter,use the variable droop coefficient method to improve the control method of the flywheel energy storage system,and use the hyperbolic tangent function to optimize the control function of the droop coefficient to increase The amount of power change of the energy storage system when it is disturbed,thereby enhancing the virtual inertia of the system,improving the quality of the DC bus voltage,reducing the power mutation of the grid-connected converter,and improving the stability of the system.Finally,a DC distribution network simulation model including a flywheel energy storage system is established in Matlab,and the results verify the effectiveness of the proposed inertial control strategy. |
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