Research On Thermal Management System For Ni-MH Battery Of Deep Hybrid Electric Vehicle

With the shortage of resources and the increasingly severe environmental problems,the world's major automobile manufacturers have started to study the deep hybrid electric vehicle(DHEV).As a new type of energy storage element for deep hybrid electric vehicle,Ni-MH battery's performance and service life have important influence on the performance and cost of the whole vehicle.With the charging and discharging of the battery,Ni-MH battery will accumulate a lot of heat.Since limited of space and time,if there is not effectively battery cooling system and a rational thermal management system,it will lead to inconsistencies in battery temperature or the temperature is too high,which will affect the power battery performance and service life.Therefore,a thorough study of Ni-MH battery thermal management system(BTMS)to improve battery service life,improve the safety operation of battery charging and discharging performance and ensure the vehicle has a very important significance.Firstly the Ni MH battery reaction principle and heat theory is carried on the theoretical analysis,and experiments are done to study the temperature characteristics of Ni-MH battery pack.The test results show that temperature affects the Ni-MH batteries on the self-discharge,DC resistance,charge and discharge efficiency and available capacity.According to the test results,a temperature index of the Ni MH battery thermal management system is presented for the deep hybrid electric vehicle.According to the power demand of the DHEV and battery thermal management system,combined with the layout of the spatial structure of vehicle,a kind of 4 rows of 5 columns battery module layout scheme is designed.Use CFX to simulate the flow and temperature field of the initial design scheme of battery group,then an optimized scheme is designed.The steady and transient temperature field of optimized battery structure is simulated and analyzed.The results show that the optimized scheme can effectively reduce the battery temperature rise,ensure the battery module,increase the temperature uniformity and meet the requirements for Ni-MH battery pack cooling system.A battery internal temperature prediction model is developed,which can predict the internal temperature of the battery module according to the heating rate,air convection heat transfer coefficient and cooling air temperature.The fan is controlled by the internal temperature of the battery,which can avoid the delay of the battery cooling caused by the surface temperature of the battery.According to the thermal model,the internal temperature of the battery is predicted to limit the power of the battery,and the correctness of the internal temperature model is verified by the bench test.The whole thermal management system is integrated into the battery management system BMS.The real vehicle test and 150 thousands km bench test show that the model has higher prediction accuracy,and the thermal management system can ensure the stability of the battery temperature while maintaining the stability of the battery.Will the thermal management system integrated in the battery management System BMS,after 15 million km of durability bench test,each battery module between the OCV,internal resistance,capacity and other parameters difference is small,battery pack consistency better resistance from 13 m k increased to 14 m Omega,battery capacity loss lost 9%,battery performance is better,and it can continue to use.After the memory effect test,it was found that the main working range of Ni-MH battery group 30%~57% was SOC,and the battery had not appeared over charging and over discharging.It is indicated that the BTMS has a good protective effect on the battery pack,and the battery temperature is maintained in a reasonable range,which ensures the good performance of the battery and prolongs the service life of the battery.