Research On Distributed Cooperative Equilibrium Control Strategy Of Modular Battery System

Large-capacity energy storage systems and power battery packs are usually connected by a large number of battery cells in series or parallel.However,due to Limitations of battery manufacturing process and complex operating conditions,there are inconsistencies between battery cells,and the overall performance of the battery pack is limited by the worst cell performance,which called "cask effect".The inconsistency of battery cells not only affects the battery capacity utilization rate of the battery pack,but also shortens the service life of the battery pack,and even causes serious safety accidents.To solve the above problem,as the focus and difficulty of battery management system(BMS)research,battery balancing system and its balancing control strategy,which can work reliably and efficiently,is the key to ensuring the long-term efficient operation of the battery pack.In this paper,multi-series lithium iron phosphate battery pack is taken as the research object.First,the HPPC(Hybrid Pulse Power Characterization)characteristic test is performed on the battery cells and the battery model is analyzed;To improve the balance efficiency and speed,increase the scalability of the system,and reduce the transfer cost of the system,based on graph theory,quantify,compare and summarize the balance efficiency of current balance converters,then design a modular battery balancing system architecture,which consists of two layers of tree structure.Secondly,perform work characteristic analysis,controller design and experimental verification of the intra-module equalization,which uses the bidirectional flyback converter,and inter-module equalization,which uses double half-bridge converter,so as to realize the basic function of the energy transfer of each balance converter,including intra-module equalization current control based on LTC3300,inter-module equalization current and output voltage control based on phase-shift + PWM control;design 576V/100 Ah high-voltage power battery system and its battery management system,and realize the basic functions such as monitoring,passive equalization,protection and relay control.Finally,study the upper layer equalization control method of the inter-module equalization converter.Considering that the battery module voltage cannot be consistent and the contradiction between output voltage deviation and current distribution accuracy in traditional droop control,according to the multi-agent system theory,design primary control,which uses droop control,and secondary control,which uses collaborative consistency control for modular battery packs.Its essence is to change the intercept and slope of the drooping curve at the same time,and jointly realize the balanced energy distribution between the battery modules and the stable bus voltage.Analyze the convergence and stability of the equilibrium control system and the influence of the relevant parameters of the cooperative control on the above performance.Finally simulation verification and scale-down platform were built to compare the equalization effects of droop control and cooperative control in three working conditions of battery pack standing,discharging,and charging,which proves the feasibility and practicability of the above equalizing system and its cooperative control strategy.It is concluded that,under the premise of satisfying stability,the communication complexity and convergence speed should be comprehensively considered to rationally design the communication network structure.