# Battery Management System Hardware Concepts: An Overview
## 3 Topologies of BMS
### Real-World Examples  
As part of a research project conducted at the authors' institute, the traction batteries of several commercially available electric vehicles have been disassembled, in order to analyse the cell ageing after a certain time of usage. As a side-product, the authors of this work were able to analyse and compare the different systems, while the disassembly was done. Thus, in the following, four real-world examples can be provided. (The data provided regarding the Tesla Model-S battery are based on a presentation by AVL [29] and our own analysis of a single module, purchased separately. The other batteries were available and disassembled completely.). Figure 3: Structure of a typical BMS for EV applications. Example (1) Mitsubishi i-MiEV  
The first example is the traction battery of a _Mitsubishi i-MiEV_ (initial registration: February 2014), shown in Figure 4a. It contains 10 Modules of eight cells and two modules with four cells, which leads to a total amount of 88 prismatic cells, all connected serially using screwed contacts. On top of each of the modules, a PCB is mounted, which--among other things--contains an LTC6802G-2. This IC is designed to monitor up to 12 lithium-ion cells, which are connected in series. The same PCB design is used for the module versions with four and eight cells. When used with four cells, the PCB is not fully populated, as four of eight available channels are not needed. The eight-cell modules use a second PCB to connect the second half of the module to the four remaining channels. The PCB on top of the modules is called the Cell Management Unit (CMU) in the official service manual for the car [30]. In addition to voltage measurement, each PCB contains three temperature sensors, which are connected to a controller located next to the Linear Technology BMS IC. Apart from the cell modules, the battery housing contains contactors (separate ones for the connection to the inverter and for DC charging), fuses, a service plug, an LEM (Freiburg im Uechtland, Switzerland) current transducer, an insulation monitor and a fan to extract cooling air. The service plug splits up the pack into two sections when it is removed. In the car, it can be found below the left hand seat. The main fuse also splits the pack in the middle. The cooling air originates from the vehicle's air conditioning system and is partially guided by short plastic pipes and forwarded to the outside by the mentioned fan. Not contained in the battery housing is the BMS master, or Battery Management Unit (BMU) [30], which communicates to the rest of the vehicle. It is located below the rear bench seat of the vehicle. The contacts, the current transducer and the insulation monitor are connected directly to the BMU. The CMUs on top of the cell modules are connected to each other and to the BMU via an internal CAN bus. Some of the signals on the battery internal CAN bus can also be found on the car's main CAN bus in lower resolution. Compared to the smart's battery, which is described below, there is a lot of free space in the iMiEV's battery housing, which may be a side effect of the air cooling. Unfortunately, for the remaining vehicles/batteries, no documentation from the manufacturers was available, thus the information provided on the other systems is less detailed than for the i-MiEV. Example (2) Smart Fortwo Electric Drive (Dt. Accumotive)  
The second example is a battery pack taken from a _smart fortwo electric drive_ (third generation, initial registration: September 2014), built by _Deutsche Accumotive_, which is shown in Figure 4c). It consists of 90 pouchbag cells, connected in series by welded connections. The cells are mounted in plastic frames, organized in three rows positioned side by side with cooling plates for a liquid cooling system mounted on top. The basic monitoring tasks are performed by ICs of TI with anonymized product code.