| With the gradual increase of the permeability of renewable energy in the power grid,the influence of power fluctuation on the safe and stable operation of the power grid is becoming more and more prominent.The battery energy storage system can complement the renewable energy to effectively stabilize its power fluctuations,and achieve friendly access to renewable energy on the grid,which has become the key component to further increase the permeability of renewable energy.In traditional battery energy storage systems,the difference in parameters between battery modules will result in the “Cannikin Law”,which seriously restricts the utilization of system capacity.Modular Multilevel Converter(MMC)not only has the advantages of good output power quality,low power switch voltage,easy to expand the voltage level,but also has a unique modular topology which can be used for distributed energy storage and grid-connection.MMC shows a great potential in the field of battery energy storage system.MMC with integrated battery energy storage,a new type energy storage device,can avoid the " Cannikin Law " using flexible power control strategy and improve the capacity utilization rate as well as the stability of the energy storage system,showing a good application prospect.In this thesis,MMC with integrated battery energy storage and its key technologies are studied from the following aspects:Firstly,the topology and working principle of the MMC with integrated battery energy storage are introduced,and the mathematical model is established.The advantages and disadvantages of various traditional multi-level modulation strategies are analyzed,and the modulation strategy suitable for the MMC with integrated battery energy storage is selected to provide the basis for the design of control strategy.Secondly,the circulation current mechanism and is analyzed,and the relation between circulation current and internal power flow in MMC with integrated battery energy storage is derived,which provides the basis to design the power control strategy.A quasi-proportion-resonant controller is designed to restrain the secondary harmonic component of circulation current,and the effectiveness of the proposed strategy is validated by simulation.Finally,the AC side and DC side power control strategy are designed based on system mathematical model,and the advantages and disadvantages of various mainstream battery power control strategy are analyzed in detail by mathematical derivation and simulation.In order to ensure all energy storage battery have same State of Charge(SOC),a novel SOC balance control strategy which consists of dc circulation control method,positive and negative sequence current injection method and the Charge and discharge regulation method is proposed.In MATLAB/Simulink,the simulation model is built to verify the effectiveness of the proposed system control strategy. |
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