Battery management system communications

Battery management systems are based on miero-controller systems. Therefore, it is possible to integrate additional, helpful features. For example, storage of historical data (data logging) and communication via the internet are possible. 

A cell phone or laptop shows battery information (often via measured and calculated means) to a local display so the communicating function is from the battery management system to the local device s screen via the host processor. Often the display is limited to the SOC, the charge or discharge status, or perhaps the run-time remaining. 

FIGURE 13.2 Example of grid-connected residential PV battery system with an energy management system as central control unit and communication interface to the distribution grid (6) (DC[Pg.296]

In contrast to lead-acid batteries, lithium-ion battery systems have always an integrated battery management, which has to be able to communicate with the power electronic components (battery inverter, charge controller) and the supervisory energy management system. Therefore, the power electronic components have to provide an appropriate interface. Furthermore, the internal battery management of the battery inverter or the charge controller, which is used for lead-acid batteries or nickel based batteries, has to be deactivated. 

Battery management can be self-contained, such as might be found in a cell phone, or it may be widely distributed as in a large vehicle battery system. In either case, there is often the need to communicate the battery state either to the user (via a display) or to the larger system (a vehicle s engine or chassis controller). 

Lithium-ion battery packs generally consist of modules coupled in series and/or parallel, and modules in turn consist of series and/or parallel coupled cells. The assembly process is shown schematically in Figure 14.13. In addition, lithium-ion battery packs also include charge and discharge controllers, a thermal management system, a module balance electronic system, and an electronic system to communicate with the outside (such as electric vehicles). Due to the very large capacity, lithium-ion battery packs have... 

In general, there are two different architectures for BMSs namely, decentralized systems and centralized systems. These two architectures are illustrated for an electric vehicle (EV) application in Fig. 8.3 (decentralized) and Fig. 8.4 (centralized). In the decentralized system (Fig. 8.3), the individual BMS tasks are located in different devices. The charge control is part of the charger, the discharge control is part of the EV drive system, the battery state determination is carried out within a range meter, and so on. Some BMS tasks must be implemented in more than one device, especially in the case of safety management. Normally, there is little or no communication between the devices, so an optimized operation is not possible. Another disadvantage is that the battery-relevant control functions are located in different devices. Thus, each device must be adapted to the particular battery used. 

In order to ensure effective communication between the battery and host device, standard methods of communication are required. One method developed by battery manufacturers and microprocessor companies is the Smart Battery System (SBS) based on the System Management Bus. In 1995, the Smart Battery Data Specification was released by the SBS Forum. These specifications detail the communications method, protocols and the data interfaces between various devices. These specifications are periodically updated and available on the forum website, www.sbs-forum.org. 

The Smart Battery communicates with the other devices (such as the SM (System Management) Bus Host and the Smart Battery Charger) via two separate communication interfaces ... 

The SMBus Host represents a piece of electronic equipment that is powered by a Smart Battery and that can communicate with the Smart Battery. The SMBus Host requests information from the battery and then uses it in the systems power management scheme and/or uses it to provide the user information about the battery s state and capabilities. The SMBus Host will also receive critical events from the Smart Battery when it detects a problem. In addition to the alarms sent to the Smart Battery Charger, it receives alarms for end of discharge, remaining capacity below the user set threshold value and remaining run time below file user set threshold value. 

A first attempt at standardization of smart batteries took place in 1993 with the introduction of the Smart Battery Specification (SBS) jointly developed by Intel and Duracell. The SBS was an attempt to standardize the communications protocol and data set for power management ICs to communicate with the rest of the system. 

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