| With the increasing global awareness of environmental protection and the increasing demand for clean energy transportation,electric vehicles have become an important direction for the development of the automotive industry.The power battery is one of the important assemblies of electric vehicles,and its performance is directly related to the range,charging time,safety,and cost of pure electric vehicles.However,the performance of lithium-ion power battery is severely degraded in low temperature environments,which directly leads to poor adaptability to low-temperature,significantly reduced driving range,and shortened battery life,which seriously restricts the popularisation of electric vehicles in cold regions.Therefore,it has become a research hotspot in the field of electric vehicles to explore the path to improve the performance of power battery in low-temperature environments and to improve the low-temperature adaptability of power battery.In this paper,based on a major provincial project,with the goal of improving the low-temperature environmental adaptability of pure electric vehicles,the lithium ion power battery pack insulation system and its application were studied.Through the power battery test,the thermophysical parameters of the battery were obtained and the low-temperature characteristics of the battery were studied;Established a threedimensional simulation model of the power battery pack,analyzed the low-temperature heat dissipation path of the power battery pack,designed a thermal insulation system scheme,and conducted experimental verification;Based on the results of battery simulation tests,a heating control strategy was developed and simulated to maintain the temperature uniformity between battery cells using a battery heating film scheme;A thermal management simulation model for a pure electric vehicle was built,and the impact of the designed power battery pack insulation system on the vehicle’s lowtemperature environmental performance was compared and analyzed through simulation tests.The research results show that the design method and scheme for the low-temperature insulation system of the power battery pack proposed in this paper can delay the temperature drop rate of the power battery pack and ensure temperature uniformity,significantly improving the low-temperature discharge performance of the power battery pack and the vehicle range.The specific research content of this paper is as follows.Firstly,the operating principle and heat generation and transfer mechanism of lithium ion power battery was analyzed,and relevant characteristic tests and performance parameter tests were conducted to obtain the thermophysical parameters of a square ternary lithium-ion power battery.The changes in internal resistance,capacity,and open circuit voltage of the battery at low-temperature was emphatically analyzed,laying a foundation for the subsequent three-dimensional simulation model building of the power battery.Secondly,based on the internal structure of the target battery pack,a Fluent threedimensional temperature field simulation model was established to explore its temperature distribution at low-temperature,and the accuracy of the model was verified through experiments.On this basis,the heat dissipation path of the power battery pack was analyzed,built a thermal resistance calculation model,obtained the thermal resistance of the insulation layer to achieve the thermal insulation goal,and designed different insulation schemes to conduct three-dimensional temperature field simulation analysis on the power battery pack,and selected the optimal scheme for experimental verification.The results show that the minimum temperature drop rate of the battery under low temperature environment is 2.989 ℃/h,which is significantly higher than that without insulation.This provides a model and experimental basis for subsequent battery temperature uniformity analysis.Then,based on the results of the battery simulation tests,a heating film was selected as the heat source to establish a heating scheme to improve the temperature uniformity,and a fuzzy control strategy was designed to control the power of the heating film to reduce the temperature difference between the cells while increasing the minimum working temperature of the cells.On this basis,the three-dimensional model is downscaled into a quasi-three-dimensional model by applying GT-SUITE,and its calculation accuracy is verified by comparing the experimental and three-dimensional simulation results,and the power battery pack temperature uniformity is simulated and analyzed.The results show that the heating solution can further improve the power pack temperature uniformity based on the insulation solution,and the temperature difference is controlled within 5℃ during the whole process,which provides data support and a model basis for the subsequent simulation of the low-temperature power battery pack insulation system and the thermal management of the whole vehicle.Finally,through the analysis of the thermal management system architecture of the studied model at low-temperature,the construction of a simulation model of the thermal management system based on a quasi-three-dimensional power battery pack insulation system model is completed,and the control strategy of the low-temperature thermal management system is formulated.On this basis,a low-temperature parking-driving condition is developed,and the vehicle performance before and after the intervention of the thermal insulation system under this condition is analyzed through simulation to verify the advantages of the thermal insulation system in improving the vehicle range and battery discharge performance under the low-temperature parking-driving condition.The results show that the insulation system designed in this paper improves the driving range of pure electric vehicles by 21.73% compared with that before the intervention under the low-temperature parking-driving condition,which effectively improves the adaptability of pure electric vehicles to the low-temperature environment. |
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