Thermal Characteristics Analysis And Cooling System Optimization Of Power Battery

In today's situation of resource shortage and environmental pollution,electric vehicles have undoubtedly become the focus of global attention and development,but there are still many technical difficulties to break through in electric vehicles.Power battery technology is one of them.The performance improvement of the power battery is closely related to the thermal characteristics and thermal management of the battery.A good battery thermal management system can maximize the performance of the power battery pack.The thermal characteristics and temperature characteristics of the power battery are the basis for studying the thermal management of the battery.It can provide reference for the control objectives and heat transfer design of the thermal management of the power battery,maximizing the performance of the power battery and prolonging the service life.To this end,this paper relies on the funding of national major special projects to adopt the test platform development-battery characteristics experiment-theoretical analysis-simulation optimization technology route,focusing on the temperature characteristics and thermal characteristics of the soft pack battery during charging and discharging,and establish and verify The mathematical model of single heat generation,and detailed analysis of the impact of various variables of the module cooling system on the thermal management performance of the module,and finally optimize the module cooling system.The specific research content and conclusions are as follows:(1)Based on LABVIEW software,this paper designs and develops a lithium-ion battery test system to study the thermal characteristics and temperature characteristics of a large-capacity(48Ah)vehicle soft-pack ternary lithium-ion battery.For the discharge performance of the battery,the operating temperature of the battery is too low,the operating voltage of the battery is lowered,the discharge power is significantly reduced,and the discharge time of the battery is also greatly shortened,and the discharge capacity is reduced.When the battery temperature is high,increasing the battery operating temperature has little effect on the performance of the battery.On the contrary,the high temperature will reduce the battery life;for the battery charging performance,the battery operating temperature is too low,the constant current charging time is shortened and the total charging is performed.It takes a long time and also reduces the charging capacity of the battery.As the operating temperature of the battery increases,the charging time is significantly reduced.After the operating temperature exceeds 35 ° C,the continuous increase of the operating temperature has little effect on the charging performance of the battery;for the internal resistance characteristic of the battery,the charging of the battery when the battery temperature is too low The internal resistance of the resistor and discharge increases rapidly,and the polarization internal resistance in the internal resistance of the discharge is most sensitive to low temperature.(2)Determine the entropy heat coefficient of each discharge state,and find that the entropy heat coefficient and temperature are only related to the discharge depth of the battery.As the depth of discharge increases,the entropy heat coefficient increases first and then decreases.The Matlab/Simulink software was used to establish the heat generation model of the single cell based on the Bernardi heat generation mechanism.The maximum relative error of the model was 4.80% and the accuracy of the heat generation model was higher by comparing the experimental temperature rise of different constant rate constant current discharge with the simulated temperature rise.By studying the internal structure and heat transfer path of the soft-packed lithium-ion battery,the cooling scheme of the bottom heat dissipation was designed and the module cooling simulation model was established by STAR-CCM+ software,and the heat generation rate calculated by the heat generation model was used as the battery.Heat source.(3)Analyze the influence of the pipe section,the thermal conductivity of the thermal conductive adhesive,the thermal conductivity of the battery body,the heat conduction path and the flow channel distribution on the thermal management performance of the module.The square pipe has a larger cross-sectional area than the circular pipe,so the pressure drop of the pipe is lower;increasing the thermal conductivity of the thermal conductive adhesive is beneficial to transferring the heat at the bottom of the battery to the cooling plate,effectively reducing the maximum temperature of the module,but at the same time The temperature difference of the module is also increased;increasing the thermal conductivity of the battery body facilitates the heat conduction at the top of the battery to improve the temperature uniformity;by increasing the heat conduction path between the top of the battery and the outer casing,the maximum temperature and temperature difference of the module can be reduced;The flow channel structure divides the internal flow channel into two flow channels and allows the coolant to flow from both sides of the cooling plate.This not only greatly reduces the inlet and outlet pressure drop but also improves the temperature uniformity of the module;the final optimized cooling scheme The maximum temperature of the battery module is 0.39 °C lower than the initial solution,and the temperature difference is reduced by 1.0 °C,which has a significant effect on reducing the temperature difference,which is increased by 31.35%.