Research On Low Temperature Thermal Control Strategy Of Electric Vehicle Power Battery System Based On Sinusoidal Alternating Current

With the increasing pressure brought by the energy shortage and environmental pollution problems,the development of new energy vehicle technology gradually becomes an important measure to alleviate this pressure.However,the operating characteristics of the battery are closely related to the temperature of the working environment in which the battery operates.An unreasonable work area may directly affect the working efficiency of the battery or even cause the battery to fail.Therefore,the development and maturation of power battery thermal management system（BTMS）technology will significantly improve the performance of power battery and positively impact the development of new energy industry.In order to investigate the low temperature performance,the effect of low temperature on charge-discharge performance and service life of lithium-ion battery was explored for the follow-up thermal management control strategy.Influence of low temperature on capacity,open-circuit voltage and the internal resistance of lithium-iron to determine the best working temperature range is researched by characteristics experiment.Based on the principle of thermogenic mechanism and heat transferring characteristics,a mathematic model of battery module preheating was established with thermal physical parameters,initial conditions and boundary conditions calculated by the experiment.According to the requirement of low temperature heating,the method of low temperature heating of sinusoidal alternating current（SAC）is proposed.The effects of current frequency and amplitude on the heating effect are investigated respectively,and the battery life and performance is verified by the change of impedance and capacity.Conclusions show that heating with large SAC amplitude at low temperature will cause irreversible degradation of the battery performance.According to this phenomenon,this paper presents a low temperature heating control strategy of constant frequency and variable amplitude of SAC to avoid lithium deposition and other side reactions.The equivalent circuit model is established by EIS impedance spectroscopy data,and based on this,the simulation analysis is carried out and compared with the experimental data to verify the effectiveness and correctness of the control strategy.Finally,the optimal current loading method was determined by comparing the heating strategies of three different time steps.The battery can be heated from-20 ℃ to5 ℃ within 509 s,the heating rate reached 2.95 ℃/min,and the heating control strategy was applied in a small battery module to verify its impact on the module added.The heating method can basically meet the rapid low-temperature heating of electric vehicles,good consistency and safety requirements.