Design And Optimization Of Battery Pack Cooling System For Pure Electric Vehicle

The charging and discharging capacity,cycle life and safety of lithium-ion batteries are greatly affected by temperature.When under high temperature conditions,the aging of the batteries accelerates and the cycle life decreases rapidly.At the same time,there is the risk of self-ignition of the batteries.To avoid this situation,it is necessary to design an efficient cooling system for the battery pack to transfer the heat from the battery pack to the environment in time.There are three main technical difficulties in the design of cooling system for pure electric vehicle power battery pack: the establishment of heat generation model of battery cell;the structural design and optimization of battery module;the design of coolant control scheme.To solve these problems,the following methods are adopted in this thesis:1.On the basis of D.Bernardi model,a modeling method of cell heating model based on open-circuit voltage fitting is proposed,that is,on the basis of cell charging and discharging test data,the open-circuit voltage of the cell is fitted to the function of environment temperature,charge-discharging ratio,State of Charge(SOC)and cycle number.Then the function is substituted into D.Bernardi model,and the improved cell heating model is obtained.2.The parametric modeling of the battery module is completed by using UG software,and the three-dimensional model of the battery module under different structural parameters is obtained from it.Then,the structural parameters of the battery module are optimized by using orthogonal test method.3.Dual-fuzzy controller is used to regulate the cooling fluid flow rate from the maximum temperature and the maximum temperature difference between the batteries,and a battery pack flow rate control verification platform is built to verify the control scheme proposed in this thesis.Based on this verification platform and the Fluent simulation platform,the flow rate control scheme proposed in this thesis and the temperature-based flow rate step-by-step control scheme are tested to verify the control effect.The test results show that the proposed modeling method is suitable for lithium iron phosphate 18650 batteries and NCR 18650 B ternary batteries,and the cell heating model established by this modeling method shows good temperature prediction.In addition,under the same conditions,the optimized module structure can reduce the maximum temperature of batteries by 3.6? and the maximum temperature difference by 3.8?.Meanwhile,the area of module decreases by 3.125e4mm2 and the cooling hydraulic pressure decreases by 100 Pa.Finally,the coolant control scheme proposed in this thesis and the temperature-based flow rate step-by-step control scheme are tested under the same conditions.The proposed scheme reduces the maximum temperature of the battery pack by 3°C and the maximum temperature difference by 1.75°C,the consumption dropped by 13.3%.