BMS topology architecture is divided into centralized and distributed. Once you see the centralized type is not that this is the mainstream? That would be wrong.

Centralized BMS structure is compact and low cost, but there are many harnesses and a limited number of channels, which are generally used in low capacity, small system size and low voltage scenarios, such as electric two-wheelers, robots, smart homes, etc.

The distributed BMS structure can be understood as a master + slave relationship, with the slave control unit responsible for collecting battery data, equalization functions, etc. The master control unit processes the data, judges battery operation, performs charging management, thermal management, fault management, etc., and communicates with external vehicle controllers, etc. in real time.

The electric vehicle power battery is developing towards high energy density, high voltage and large volume. The distributed BMS architecture is mainly used in hybrid and pure electric vehicles, such as BMW i3/i8/X1, Tesla Model S/X, BYD Qin, etc. Although the control is complicated and cost is higher, but it is better in flexibility and less wiring harness.

Based on the distributed BMS architecture, we classify the chips as follows.

Data acquisition part

AFE (Analog Front End): AFE refers to the battery monitoring chip, mainly with various sensors to collect cell voltage, temperature and other information, only with parameter monitoring functions. In addition, AFE generally integrates passive equalization technology. Here mention what is battery equalization, as mentioned above, generally in high series battery pack, the voltage and power of each cell will be different, in order to ensure the power balance between, so take active equalization or passive equalization.

Passive equalization uses passive devices to consume excess power through resistive heating of the cells with more power, while active equalization transfers excess power to achieve energy flow between cells. Passive equalization is low cost and high reliability but increases system loss. Active equalization requires more components and is costly, but helps to reduce system losses.

Power metering chip: collects battery information and uses specific algorithms to estimate parameters such as SOC (state of charge, i.e. remaining power) and SOH (state of health, i.e. aging) of the battery, and transmits the results to the control chip.

Control part

Battery protection chip: Monitor the battery charging and discharging conditions, including over-voltage, over-current, overheating, etc. Once abnormal conditions are found, the circuit can be cut off in time to protect the safety of the battery system. At present, some of the metering and charging chips will integrate the battery protection function.

Charge management chip: mainly responsible for charge and discharge management. According to the characteristics of lithium battery automatically pre-charge, constant current charging, constant voltage charging. The charge management chip makes the voltage and current reach a controllable state, which can effectively control the charging state at each stage of charging and protect the battery from over-discharging, over-voltage, over-charging and over-temperature, which is ultimately beneficial to the battery life continuation.

Charge management chips can be divided into switch, linear, and switched capacitor depending on the working mode. Switching type is suitable for high-current applications and has flexibility, commonly used fast charging solutions are using switching type; linear is generally used in low-power charging scenarios, such as portable electronic devices; switching capacitor type

charging efficiency, but the architecture is limited, generally used with the switching type.

MCU: responsible for relay control, SOC/SOH estimation, battery data collection, storage, etc. Need to meet AEC-Q100, ISO26262 and other certifications. Compared with consumer-grade and industrial-grade MCUs, automotive-grade MCUs have higher barriers and have hard requirements for reliability, consistency, safety and stability.

Communication part

Digital isolation device: In BMS system, SOX (including SOC, SOH, etc.) algorithm is usually executed in MCU, so digital isolation device is usually used to communicate between AFE and MCU.

Currently, the mainstream communication architecture is daisy-chain architecture, where each AFE is connected to each other and then connected to MCU through an isolated communication chip, reducing the number of communication chips. The advantage of daisy-chain architecture over CAN bus is that once the middle is disconnected, the AFE chips behind can continue to communicate.