92 Chapter 8 lithium-ion needs to be managed in order to ensure its safety. A lead–acid battery, for instance, easily operates with no form of electronic controls as it is more easily able to accept abusive conditions without going into thermal runaway-type events. Lithium-ion, on the other hand, must be managed to ensure that the cells stay below their maximum and minimum voltage, temperature, and current limits. This chapter will provide the reader with a very brief overview of the BMS, its functionality, and its hardware.
For a more detailed review of the BMS and its operation, I would recom- mend Davide Andrea’s well-written book Battery Management Systems for Large Lithium- Ion Packs (Andrea, 2010). Andrea covers all topics in great detail from general descriptions to how to design and build your own BMS. BMS Typologies There are two basic types of BMS system topologies, a centralized BMS and a distributed BMS. The main difference between the two is where the hardware is mounted. This is of course a major simplification but is relatively accurate. The host, or master, control unit usually encompasses the majority of the functionality of the ESS:
(1) opening and closing the contactors, monitoring the temperature of the pack, and communicating with the cell control boards to monitor the cell temperatures; (2) monitors the voltage of the pack and cell control boards; (3) manages the heating and/or cooling (turning it on and off) based on the tempera- ture readings; (4) manages the safety (opening and closing the contactors based on the voltage and temperature and SOx); (5) calculates, manages, and tracks the SOx functions, and communicates with the vehicle (or other master system). The controller is made up of two main components:
a hardware controller board and a large amount of software “algorithms” that ensure the performance and safety of the complete system. In a centralized BMS system, the main control board as well as the cell-monitoring control boards are all colocated in one unit with wiring harnesses spanning throughout the pack connecting to all of the cells ( Figure 1 ). This minimizes the amount of hardware but increases the amount of wiring needed in the pack. In the distributed BMS structure ( Figure 2 ), there is a “host” or “master” controller that is centrally located and there are multiple separate boards to monitor the cells that are usually mounted directly to the cells or modules.
This reduces the wiring needed as the slave boards tend to be connected in a daisy chain manner. But it also tends to drive up the cost as it increases the amount of PCB type hardware that is required. However, the distributed BMS design is often used to offer greater functionality and control within the system as each slave board controls only a limited number of cells. There is some variability in the BMS architecture as the types of typologies actually vary across a continuum with the distributed at one end and the centralized at the other end.