Multi-Chemistry Battery Management System for Electric Vehicles

Abstract

Electric vehicle technology is increasing its market share through its sound development. Battery management systems (BMS) also play an essential role in this technology regarding efficiency, safety, and meeting the end user’s expectations. In this study, a simulation study of a multi-chemistry BMS capable of real-time switching has been carried out so that the system can operate more efficiently. The proposed system aims to increase efficiency and performance using two batteries with different characteristics. The primary battery chemistry used is lithium titanate oxide (LTO) batteries, which can provide higher instantaneous power in times of high power demand. The second battery chemistry is lithium iron phosphate (LFP) batteries, which have higher endurance due to their high energy density. Each battery has six modules and provides a total voltage of 450 volts. The WLTP Class 3 driving cycle was used as the vehicle’s speed reference in the simulation, considering its power/weight ratio. The battery control signal required for switching between batteries is produced according to the instantaneous power requirement of the vehicle. For this, the acceleration value is calculated, and the transition from one battery to the other is determined accordingly. If the acceleration is above the threshold value of 0.75, the LTO battery is connected. In the other case, the LFP battery is connected. Contactors are used to provide switching between batteries but not IGBTs. Consequently, contactors can be used as switching elements with a transition window of 3 seconds. This technic is less costly than designing such a system with fast-switching circuit elements like IGBT. In addition, the multi-battery mechanism consisting of LTO and LFP chemistries showed better performance than a battery pack with only LFP chemistry with the same specs. In other words, multi-chemistry BMS provides a significant performance and efficiency increase.