Testing study of commercially available lithium-ion battery cell for electric vehicle

Lithium ion cells have been a major energy source of Electric Vehicles (EVs) for recent years. Multiple cells connected in series and parallel make a complete battery pack to drive EVs. Lack of information about the battery's safe operating points can lead to degradation of cell's life. Therefore, it is important to supervise the states of a lithium ion cell, particularly its State of Charge (SoC) and the effect of EV's speed on open circuit voltage. The Open Circuit Voltage (OCV) is crucial for SoC estimation and for the effect of speed on battery cells. In this paper, the implementation of pulse discharge test at room temperature is presented to measure states of lithium ion cell. In addition, an induction's motor model with a current controller is designed for EV's speed estimation and for the establishment of a relationship between speed and the current drawn by the vehicle. The experiments are conducted on Lithium iron phosphate cells to establish a relation between OCV and SoC. The results verify that as the load current increases, the new open circuit voltage level established will be low as compared to initial cell voltage level.