Thermal model for square lithium-ion battery pack

Firstly, the specific heat capacity of battery cell and its overall heat transfer coefficient under natural cooling condition as well as the thermal conductivity of cooling channel material in a square lithium-ion battery pack are estimated by least square method. Then calculation formulae of local combined heat transfer coefficient of cooling channel surface under forced cooling condition are worked out based on thermal boundary layer theory. Finally a one-dimensional transient heat transfer model is set up according to the structural feature and cooling mode of battery pack. With the model, the operating temperature of each cell in battery pack can be predicted realtime according to ambient temperature and the operating load, cooling intensity and initial SOC of battery pack. The temperature distribution of battery cell in a 144V/8Ah square lithium-ion battery pack under different operation conditions are measured on a Arbin test bench and compared with that by model simulation and the results show that the maximum error of model simulation in temperature is only 1°C, meeting the accuracy requirements for the performance simulation and battery pack management strategy optimization of hybrid power system.