CHAPTER 8 Battery Management System Controls The Battery Management System (BMS), while it may have many other names, is the central control unit of the battery pack. It is essentially (and quite literally) the “brains” of the operation. The BMS is a combination of several component systems, including a host or master controller (a Printed Circuit Board (PCB)), a series of “slave” control boards (depending on system typography), sensors, and software that makes everything work together.
Some people also expand the definition of a BMS to include the control electronics such as the switches, fuses, high-voltage front end, high-voltage interlock loop, and disconnects; however, for the purposes of this book, I have separated those components out into a separate chapter on System Control Electronics (Chapter 9). What, then, does a BMS do in a lithium-ion battery system? In short, the BMS provides protection against overcharging, overdischarging, high temperatures, low temperatures, short circuiting, and other failure modes.
In addition to protection, the BMS offers monitoring functionality; in fact the protection would be useless without the ability to monitor the state of the battery and cells. The BMS also communicates both internally within the pack as well as to the outside controllers and systems. Finally, the BMS provides optimization and maximization of the batteries performance, ensuring that the user can get the best performance out of the battery at any time. Overlaid on top of all of these are the software calculations that estimate the various factors within the battery such as the state of health (SOH), the state of charge (SOC), maximum voltage, etc.
That describes the “what” of the BMS; the “why” then is relatively simple. Why does a lithium-ion battery pack need a BMS? In short, the BMS ensures the safety and life of the battery pack. The BMS manages the amount of power and energy in the pack to achieve the desired lifetime of the pack. Most portable power batteries for laptops and similar devices only need to provide energy and power over a year or two and are generally operated in a narrow temperature range. How often do you leave your laptop outside in the middle of winter?
On the other hand, the automotive and industrial batteries must last from 8 to 10 or even 15 years or longer and will need to survive in a very wide range of temperatures from the Arizona desert summers to the extremely cold winters of the northern regions. Can a lithium-ion battery be used without a BMS? I have heard of some racing type EV applications where they claim to have no BMS in the system. But these are typically one- or two-use applications; the life of the battery may only need to last for one racing season and will be stressed to the extreme so warranty and longevity are not concerns. But overall, no production application will be designed without a BMS.
Compared to other cell chemistries, The Handbook of Lithium-Ion Battery Pack Design. http://dx.doi.org/10.1016/B978-0-12-801456-1.00008-7 Copyright © 2015 Elsevier Inc. All rights reserved. 91