# Analysis and Synthesis of Architectures for Automotive Battery Management Systems
## 4 Analysis of Centralized BMS Architectures  
### Design of a Centralized BMS  
Through the application of a centralized processing unit in a BMS as presented in Figure 4, different aspects must be determined. There are several possible architectures to integrate the BMS, as shown in Figure 1. In the following domain vehicle control units (VCU) and powertrain domains (PD) are focused on, since those are more likely to exist in various vehicles soon. Nevertheless, all aspects of the following work can be applied for all centralized architectures. The PD includes the BMS master functionalities in a layer, without that there is a need for a distributed BMS unit. The communication between PD and the slave units is a daisy-chain. This section describes the opportunities and risks of a centralized BMS and therefore performs a virtual synthesis of such a system.  
The functions and tasks of a BMS can be processed by a central PD or a VCU in a centralized architecture. A centralized computing unit such as the VCU, which is used to define the state values of the battery, could use information of other control units more easily for new features in case of the BMS. In return, the BMS could share its raw data with the other subsystems with high resolution. Therefore, the BMS might obtain access to rotation speeds of the wheels and the electric machine, GPS speed and acceleration data. Moreover, there is now access to the in-body resistance and temperature of the electric machine. This data helps to precisely predict the vehicle range. The data can be used to adopt the inverter control strategy to the inner resistor of the electric machine to avoid power differences of vehicle tranches. Furthermore, the measurement modules could participate as sensor units only and the architecture can be simplified due to this.  
The single slave modules calculate the measured voltages and temperatures. Because the measurement physics need resistors to determine the values, the slave modules need to have a small control unit. In today's conventional EV batteries with smaller cells, e.g., 21,700, and a modular design an overall sum of around 7000 cells, makes a complex slave module arrangement necessary. The upcoming cell-to-pack design with 30-40 cells enables a more centralized slave module design, see Figure 5. It is then conceivable to connect all cells of a battery with only one slave module. A direct connection to the PD is not expedient due to the then numerous cable connections through the temperature (often 4-wire measurement) and voltage measurement. With prismatic cells in a cell-to-pack design, a high level of the integration of cells, slave module and junction box is possible. For this reason, the design saves installation space or enables high ranges through better utilization of space and thus a high energy density of the battery. The junction box contains components that are sensibly located in the immediate vicinity of the HV-lines of the battery in order to avoid electrical hazards. The positioning of the slave module is more flexible. The BMS's computing unit can be put on one controlling unit (e.g., PD), where the different measurements of the slave modules are post processed.  
Figure 5: Scale representation of a 400 V battery with prismatic cells and a capacity of about 60 kWh in conventional design (**left**) and cell-to-pack design (**right**).