Comparative Analyses of the Response of Core Temperature of a Lithium Ion Battery under Various Drive Cycles

Core temperature (Tc) estimation, State of Charge (SOC) and State of Health (SOH) are the key algorithms in any Battery Management System (BMS). During high-speed operation of the Electric Vehicle (EV), large current is drawn from the battery due to which Tc reaches a higher value than surface temperature (Ts). This leads to thermal runaway causing degradation in SOH, resulting in increased internal resistance and/or reduction in capacity. In the present work, Tc for a Lithium (Li) ion cell under various drive cycles is estimated using Kalman Filter. Based on governing coupled heat transfer equations, Tc is modeled using measured Ts and ambient temperature (Tamb). Simulation was carried out using MATLAB/Simulink software using “Commonly Used Blocks”. The standard drive cycle pattern was chosen from the “Vehicle Dynamics Blockset” available in the software. Using the dynamic equation of the EV, the velocity profile was converted to current and was fed as one of the inputs to the thermal model. A simple cell model consisting of 1 RC pair was used for obtaining the Open Circuit Voltage (OCV) and terminal voltage used for Tc estimation. The OCV – SOC values were modeled as a 1-D lookup table in Simulink. It was observed that Tc and Ts closely followed the current pattern and Tc > Ts during current discharge. Among all the drive cycles considered, Highway Fuel Economy Test (HWFET) showed maximum Tc of 300.9K, thereby highlighting the importance of simulation studies before hardware development.