Research On Key Technologies Of Energy Storage MMC In Wind Storage And Grid-connected Systems

Affected by environmental factors,the grid-connected output of new energy has a certain degree of dynamics and stability,which will affect the grid-connected stability of the power system.The role of energy storage system in storing and releasing energy will enhance the stability of the power system to a large extent,improve the power quality,and inhibit the power fluctuation after the new energy is put into the grid.Therefore,good power electronic components and energy storage systems are of great significance to the research on the safe grid connection of new energy sources.Many of the current energy storage systems connect a large number of energy storage units in series and parallel to the energy storage converter.If one energy storage unit is damaged,it may affect the operation of the overall energy storage system.The special sub-module cascade structure of MMC can improve the stability and reliability of energy storage system operation.So in this paper,it takes energy storage MMC as the research object,the working principle,mathematical model and control mode of energy storage MMC and the application of energy storage MMC in wind power grid-connected system are studied.In this paper,the topological structure,mathematical model,working principle and modulation mode of the energy storage MMC are described first,and the SOC equilibrium control strategy of energy storage MMC is summarized.The energy storage MMC was applied to the wind storage grid-connected system,and the model of the wind storage grid-connected system was modeled by using the energy storage MMC parallel to the PCC point.At the same time,a hybrid energy storage system topology based on MMC is proposed,which combines batteries and super capacitors to improve the energy density and power density of the topology,and the mathematical model of storage battery,super capacitor and related storage controller is given.According to the structural characteristics of the wind storage grid-connected system,a grid-connected control strategy to suppress wind power fluctuations in an ideal grid is proposed.According to the law of power conservation,the energy management strategy of the wind storage grid-connected system are given,the SOC limit management for super capacitors is propose.Secondly,a low-pass filtering algorithm was used to allocate the high and low frequency bands of energy storage to super capacitors and batteries,and a cloud model algorithm was used to optimize the time constant in the low-pass filtering method to further rationally utilize the energy storage capacity.Finally,the power balance of the grid-connected system is realized by controlling MMC and energy storage equipment.Based on MATLAB/SIMULINK simulation platform,the energy storage MMC model is established and verified by simulation.The simulation results show the applicability of the energy storage MMC.Secondly,the wind storage grid-connected simulation model based on hybrid energy storage MMC was established,and the grid-connection control strategy was simulated and verified under two conditions of wind power constant and wind power fluctuation.The results show the effectiveness of the proposed wind storage grid-connected system topology and grid-connected control strategy.