Design Of Heat Management System For Lithium-ion Power Battery

As the emergence of the problem of energy shortage and the environment issues among the worldwide,the electric vehicle which is considered to be the representative of the new energy vehicle has become the research focus of the automobile enterprise and the research institute around the world.And the lithium ion batteries,which are the most important component of electric vehicle must be the main reason that restricts the development of the electric vehicle.As the most widely used power battery,the performance of lithium ion batteries is largely influenced by temperature.In the high temperature environment,the rapid accumulation of the battery temperature may cause safety issues,even cause the battery to fire and burn.In low temperature environment,it is difficult to charge the battery,and the available capacity is reduced seriously,internal resistance becomes larger.Appropriate cooling of the battery at high temperature and proper heating of the battery at low temperature are important,it can improve the working environment and performance of the battery.First of all,a lumped parameter thermal simulation model of the battery is established to analyze the temperature rise of the electric bus battery system under the operation conditions of the driving cycles of the Harbin city electric buses.Moreover,the quantitative relationship between the optimum heat transfer coefficient of the battery and the ambient temperature was investigated.The relationship between the temperature rise(Tr),the number of cycles(c),and the heat transfer coefficient(h)under three Harbin bus cycles have been investigated at 30°C,because it can provide a basis for the design of the battery thermal management system at high temperature.The results indicated that the heat transfer coefficient that meets the requirements of the battery thermal management system is the cubic power function of the ambient temperature.Therefore,if the ambient temperature is 30°C,the heat transfer coefficient should be at least 12 W/m2 K in the regular bus lines,22 W/m2 K in the bus rapid transit lines,and 32 W/m2 K in the suburban lines.It is proved that the temperature rise of the battery,the number of cycles and the coefficient of heat transfer are approximately linear.Then the temperature rise of the battery is analyzed by the lumped parameter thermal model when the batteries are heated by short pulse,the quantitative relationship between charge-discharge ratio and preheating time is obtained.The simulation results show that the preheating time and charge-discharge ratio satisfy the exponential function relation.It can provide a basis for the design of the battery thermal management system at low temperature.Then the finite element model of the heat field of the battery pack is established.The thermal field and temperature change of the battery pack which heated by electric heating film under low temperature environment are simulated and analyzed.The optimum coverage rate of heating film is obtained.It can provide a basis for the design of the battery thermal management system at low temperature.