Components of a single battery Single cell is the basic...
BCU
Introduction: The BCU is the brain of the BMS, which contains an MCU chip responsible for calculating the State of Heath (SOH) and State of Charge (SOC) of the battery, and making judgments and decisions by using the accurate battery data measured by CSC and BJB to ensure the safety of the battery and improve the performance. It can also coordinate the battery balancing function of the BMS.
What is a BCU
As shown in Figure 3-1, there is no BCU in a low-voltage system. In a low-voltage system, CSU, BCU, and BDU are generally combined together, and the concept of BCU exists only when the system is above 48V.
Figure 3-1: Low pressure BMS
Figure 3-2 shows a typical block diagram of BCU in a high-voltage system. BCU is composed of a communication chip and MCU, and MCU is the main control. The communication chip is the bridge connecting MCU with CSU and BJB, and can convert the signal from the CSU and BJB Daisy chain into a decoded bit stream and send it to MCU. The MCU chip can process the information collected by the BMS AFE chip and calculate the state of charge (SOC). At the same time, the MCU polls all the information measured by the CSU and BJB, calculates the battery status and responds to the fault or diagnosis from the CSU and BJB. The BMS MCU chip needs to accurately calculate the SOC. And that requires a lot of skill and experience.
Figure 3-2: Typical BCU (BMU) block diagram
In the traditional BJB, the BCU not only undertakes the monitoring of SOC/SOH, but also is responsible for current detection, insulation detection, link diagnosis, charge and discharge relay drive control and other functions. After the emergence of intelligent BJB, as shown in Figure 3-3, the previous tasks related to diagnosis and control of BCU were transferred to the core UIR chip of intelligent BJB for processing, and BCU began to complete SOC and SOH work more purely.
Figure 3-3: Schematic diagram of a BCU with UIR
Evaluation of BCU performance parameters
Although BCU is responsible for the SOC and SOH of BMS, this part is strongly related to the software algorithm, MCU is mainly a control function, there is not a lot of computing needs, so the choice of MCU is more flexible, but must meet the ASIL D security level, such as NXP's S32K3 series. Take S32K3 and TMS570LS0432 as examples, the basic version of S32K3 is single-core M7, operating frequency 120MHz, the advanced version is multi-core M7 with locking step function, operating frequency 240MHz, TMS570LS0432 dual R4 locking step core, operating frequency 80MHz, the peripheral interface will not be described here. The core selection points of the MCU for automotive BCU are as follows: 1# : meet the safety level of ASIL D 2# : multi-core M4-M7, R4-R4F, priority lock step core
CONCLUSION
In view of the high standard and complex working conditions of the vehicle, the vehicle BCU must support the internal SOC and SOH algorithm updatability, generally through CAN remote upgrade, and in different seasons, different ambient temperatures, the implementation of different charging and discharging, cell balance strategy, as far as possible to maintain the consistency of the cell, in order to slow down the battery decay rate.
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