Research On Equalization System Of Lithium Battery Pack For Electric Vehicle Based On Quasi-Resonant Switched-capacitor

With the increasing problems of energy crisis and environmental pollution,the development of electric vehicles has attracted the attention of many countries.Lithium-ion battery as one of the core component of the electric vehicle,during the manufacturing process,the consistency of the internal resistance,capacity,self-discharge rate and other parameters of the single cell cannot be guaranteed,and due to environmental factors such as temperature during use,unbalanced phenomena of inconsistent cell voltage and capacity will occur during the actual charging and discharging cycle,which increases with the number of charging and discharging.It will affect the life and safety of battery.This paper takes the lithium battery pack of electric vehicles as the research object and builds an equalization system based on quasi-resonant switched-capacitors.In this paper,we firstly use graph theory analysis method to establish graph theory models of several types of switched-capacitor equalizer,and compare their performance in terms of equalization efficiency,equalization speed,cost and reliability,and select the superior performance equalizer---Delta-structured for further research.Secondly,this paper proposes the application of resonance technology in the switched capacitor equalization circuit,which can not only achieve zero-current-switching of the switch,reduce losses,but also further accelerate the equalization speed and improve the performance of the equalizer.Aiming at the defect of the volume and cost of the Delta-structured quasi-resonant switched-capacitor equalizer in a large series lithium battery pack,a two-layer structure balancing system is proposed.The lower layer is set for the internal cells of the module,to achieve the cell balancing of each module.The upper layer is set for the whole battery pack to achieve the balancing among battery modules.And take the application of 96 series battery packs as an example to analyze the performance of the double-layer equalization system composed of different monomers in the module and choose the structure of the 8-cell double-layer Delta-structured quasi-resonant switched-capacitor equalization system.Finally,a double-layer Delta-structured quasi-resonant switched-capacitor equalizer model was built in PSIM,and a prototype of 4-cell Delta-structured quasi-resonant switched-capacitor equalizer was also produced.Both simulation and experimental results showed that the quasi-resonant switched-capacitor equalizer can not only realize zero-current-switching,but also further accelerate the equalization speed,and verify the performance of the double-layer Delta-structured quasi-resonant switched-capacitor equalizer.