| In today’s trend of environmental pollution and energy shortage,the development and importance of electric vehicles is becoming more and more obvious worldwide,and many automobile manufacturers have started to develop and produce electric vehicles in large quantities.As the core component in electric vehicles,the performance of the battery system directly affects the service life,driving range,driving safety and other factors of electric vehicles.At present,lithium-ion batteries have become the necessary choice for electric vehicle batteries due to their high energy density,long service life and no memory effect.Although lithium-ion batteries are widely used in electric vehicles due to their excellent performance,there are still some problems.Lithium-ion batteries release heat during charging and discharging,and if the heat in them is not dispersed in time,it is easy to cause the accumulation of heat inside the lithium battery,leading to malfunction or danger in electric vehicles and affecting driving safety.Therefore,it is necessary to study the heat dissipation characteristics of lithium-ion batteries and their use under different conditions to ensure the safety and reliability of lithium batteries in the operation of electric vehicles.This project takes lithium-ion battery as the research object,simulates the lithiumion battery monomer and battery packs,analyzes the temperature field and heat dissipation mode of lithium-ion battery under different conditions,and optimizes the thermal performance of the battery pack by using orthogonal experimental design,BP neural network and multi-objective optimization algorithm.Since the optimal operating range of Li-ion battery is 293.15～313.15 K and the maximum temperature difference is not higher than 5K,the maximum temperature and maximum temperature difference of Li-ion battery are selected as the optimized design objectives,and the best combination of parameters of Li-ion battery is obtained to improve the thermal efficiency of Li-ion battery pack.The main research of this paper is as follows.1.A staggered bidirectional flow cooling design scheme is designed to study the temperature distribution of a lithium battery pack with a discharge multiplier of 3C under different influencing factors.The design scheme has a good temperature control effect on the heat dissipation of the lithium battery pack,and the maximum temperature of the battery pack can be ensured to be in the optimal operating range by changing the influencing parameters.2.Through orthogonal tests,the main order of the factors affecting the maximum temperature difference of the Li-ion battery pack is coolant temperature,battery embedding distance to the cooling plate and coolant flow rate,among which increasing the coolant temperature can obviously improve the uniformity of Li-ion battery pack temperature,and the optimized combination is C4A4B1,which means the battery embedding distance is 4mm,the coolant flow rate is 0.003m/s,and the coolant temperature is 303.15 K.Although the heat dissipation requirement of the battery pack is satisfied,the highest temperature is concentrated in the center of the battery pack,so further optimization is made.3.The combination of multi-objective optimization and BP neural network is used to optimize the prediction model of BP neural network by multi-objective optimization algorithm,and a set of Pareto optimal set is obtained.Considering that the maximum temperature of the battery pack is within a reasonable range,the maximum temperature difference in the Pareto optimal solution set is used as the optimized design solution.The result obtained from the Pareto optimal solution design is(308.86,3.13),and the corresponding battery pack embedding cooling plate distance,coolant flow rate and temperature are 3.954 mm,0.0059m/s and 303.128 K.4.Based on the parameters in the optimal solution,they were brought into Fluent for numerical simulation,and compared with the optimal combination of orthogonal tests,the maximum temperature difference was reduced from 3.39 K to 3.15 K,a reduction of 7.08%;the final temperature difference was reduced from 3.25 K to 2.35 K,which was 27.7%.It produced a better improvement for minimizing the maximum temperature of the Li-ion battery pack and the uniformity among the battery cells. |
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