# Analysis and Synthesis of Architectures for Automotive Battery Management Systems
## 5 Methodical Approach to the Synthesis of BMS Architectures
From the considerations in the earlier sections, a consolidated list of the main functions of the BMS can be generated:  
* Safely start-up and shut down the system (in normal operation or in case of a major error e.g., a crash),
* Measure the voltage of each individual cell,
* measure the discharge and charge current of the individual cells, of sub-modules and/or of the whole vehicle battery,
* measure the temperature at certain points of the battery,
* estimate the state of charge (SoC) of the individual cells, of sub-modules and/or of the whole vehicle battery,
* estimate the state of health (SoH) of the individual cells, of sub-modules and/or of the whole vehicle battery,
* balance the charging voltage resp. current of the individual cells and of sub-modules,
* balance the discharging voltage resp. current of the individual cells and of sub-modules,
* protect the cells from overheating,
* prepare the cells for high-speed charging or discharging and
* communicate with the drive train and the human machine interface (HMI). Additional functions would be the estimations of the state of life (SoF) and the state of available power (SoP) as well as a protection of over- and under voltage and the early  
Figure 6: V-model including synthesis process steps. prediction of thermal runaways. Figure 7 presents the main functions, which were analyzed concerning their mutual interaction in the form of a function interaction matrix. This matrix displays the interactions, allows to identify functions with a high level of interaction and thus increases the transparency of functional interaction. The core synthesis of E/E-architectures can be carried out by means of topology optimization algorithms; this topology optimization requires an abstract model of these architectures and appropriate optimization criteria. One possibility is described by [PERSON] and [PERSON] [47], who employ an optimization function, which is based on the design structure matrix and axiomatic design theory. Similar approaches employ product function matrices [48] as well as a combination of the Multi-Domain Matrix (MDM) and functional models [49]. It is also possible to create these possibilities manually, keeping in mind the requirements, the BMS functions and the functional relationships. An evaluation of these possibilities can be based on a diagram, as shown in Figure 8.  
Visible in Figure 8 are the two ends of the solution continuum. One is a completely centralized solution, with only one central processing unit and all sensors directly connected to the central processing unit. The other end is a completely decentralised solution, within which all sensors are connected to slave units in the direct surroundings and all processing is conducted by a large network of slaves; a central processing unit does not even exist. Figure 8: Evaluation of E/E-architectures. Figure 7: Function interaction matrix. The synthesized solutions will be a compromise between these extremes, and the best of them will probably achieve characteristics that are on the line of the probable optimum, as visible in Figure 8. It can be concluded that a centralised solution is desirable for, amongst others, economic reasons. A centralised E/E-architecture of the BMS can only be sensibly achieved if both hardware and software functions are realised in central entities. This kind of software integration will pose additional challenges on the product development process and will require a methodological procedure style according to the V-model and continuous simulation and HiL-tests (see also Figure 6). Obviously, a holistic evaluation has to consider a large number of further criteria, which mainly result from the requirements collected in the early phases of the architecture development process (compare Figure 6) and managed throughout the process [50]. Important evaluation criteria range from communication and update possibilities, over diagnosis possibilities to the capability to accommodate faults [51].