Development of battery management system in EV application using wireless communication

Abstract

The lithium-ion battery pack is a very important part of an electric vehicle (EV) and is an expensive component. If there is no proper battery management system (BMS) for the lithium-ion battery pack, the overall performance could be affected in several ways, including the lifecycle, charging-discharging behaviour, safety and ambient temperature. Because a battery pack is exposed to different conditions, such as ambient temperature, aging and manufacturing variation, over state of charge (SOC) and under depth of discharge (DOD), the charge of the series connected cells becomes unbalanced. During the rapid charge balancing (transferring) process, the internal temperature of the cells may exceed its allowable limit (46°C) which results in unstable balancing behaviour. Besides this, communication makes the BMS convenient and even smarter by connecting all the sensors, including the sensors for voltage, current, SOC and temperature, of the battery pack. However, a large number of wire terminations in the BMS, including among the sensors, are liable to safety failure and are not fully reliable. To help address these issues, this research focuses on developing a BMS that includes a charge balancing system and wireless communication system for three series connected battery cells. Several local control units and one central controller are used to achieve this. The charge balancing system uses a DC to DC converter and a controlled algorithm, which considers internal ambient temperature, to overcome the challenges associated with the charge balancing process. With this approach, the increasing internal temperatures in the battery cells are maintained within the range of 27°C to 35°C. Real time information is monitored and used to control the functionality of the battery pack using wireless communication. The wireless communication system, using the ZigBee communication protocol and point-to-point topology, has reduced wiring problems, as well as size and cost, compared to the conventional communication system. The simulation results of this system have been verified by the experimental results. The wireless communication and control management system developed in this research can be applied to large battery packs to improve their overall performance.