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