| Energy storage system plays an important role in maintaining short-term power balance,improving power quality and power-generating quality in the micro-grid.Lithium batteries are particularly suitable for micro-grid with its advantage of high energy,long cycle life and high efficiency.In this paper,a modular multi-level energy storage converter is proposed for the application of DC micro-grid.The modular multi-level energy storage converter is not only maintains the conventional energy storage converter's characteristic of controlling the two-way flow of energy,but also can independently modulate the battery charge and discharge rate.It has a strong engineering application value with the combination of energy storage converters and lithium battery equalization circuits.Firstly,the background and significance of the research are introduced.The important role of energy storage system in micro-grid is discussed.The research progress of energy storage converter and lithium battery equalization circuit is introduced.The design idea of combining energy storage converter and lithium battery balance control is expounded.A topology scheme of modular multi-level energy storage converter is proposed,based on the research status of MMC in AC energy storage system and the research progress of DC energy storage converter.Then,the control strategy of modular multi-level energy storage converter is discussed.The closed-loop control strategy of voltage and current with voltage feed-forward and the closed-loop control strategy of power current are designed.Theequilibrium control strategy based on duty cycle fine tuning and its condition are discussed.In order to realize the power balance between modules,an equalization control strategy based on sub-module bypass and lock access is proposed.The control strategy of energy storage system applied to DC micro-grid is designed according to the actual situation of DC microgrid,.Finally,a simulation model of modular multi-level energy storage converter is built in Matlab/Simulink environment The closed-loop power control strategy and the equilibrium control strategy under several different conditions are simulated and analyzed.Carried out the corresponding experimental verification.based on TMS320F28335 experimental platform.The experimental results show the effectiveness and feasibility of the modular multi-level energy storage converter and its control strategy proposed by this research. |
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