Battery management system (BMS) is an important link between on-board power battery and electric vehicle. BMS collects, processes and stores important information during the operation of the battery pack in real time, exchanges information with external devices such as the vehicle controller, and solves key issues such as safety, availability, ease of use, and service life in the lithium battery system. The main purpose is to improve the utilization rate of the battery, prevent overcharging and excessive discharge of the battery, extend the service life of the battery, and monitor the status of the battery. Generally speaking, it is a system for managing, controlling and using battery packs.

Why batteries need to be managed

Can't the battery be directly connected to the motor for power supply? Need management? What do you want to manage? First of all, battery is a very delicate thing. Its capacity is not constant, and will continue to decay with the continuous charging and discharging in the life cycle. The rate of decay is related to many factors, such as whether it is overcharged and discharged, whether the ambient temperature is appropriate, and how long it takes to experience charging and discharging. Especially at present, lithium batteries with extremely high energy density have become the mainstream. They are more sensitive to these factors. Once overcharged or discharged, or the temperature is too high or too low, it will seriously affect the battery life and even cause permanent damage.

An electric vehicle does not use a single battery, but a packaged battery pack composed of many cells in series or parallel. The voltage required by the motor driving the vehicle is much higher than that of a single battery cell, and the same is true of the power required to reach the predetermined range. Therefore, it is necessary to reach the predetermined design voltage by connecting multiple cells in series; Then, these series cells are connected in parallel to reach the predetermined design capacity, and finally packaged into a large battery pack. Theoretically, each cell in the whole battery pack should be the same. However, due to the differences of each cell itself and the different heat dissipation conditions caused by the different actual positions, the working conditions of the cells are different.

As long as a battery cell is overcharged or discharged, the battery pack will have problems, which is the same as the fact that the capacity of a bucket to hold water is determined by the shortest board. Therefore, it is necessary to monitor and manage a single battery saver - that is the meaning of BMS.

BMS system architecture

1. Main board: collect the sampling information from each slave board, communicate with the vehicle through the low-voltage electrical interface, control the relay action in the BDU, monitor the various states of the battery, and ensure the safe use of the battery during charging and discharging;

2. Slave board: monitors the unit voltage, unit temperature and other information of the module, transmits the information to the main board, and has the battery equalization function. The communication mode between the slave board and the main board is usually CAN communication or daisy chain communication;

3. BDU: connected with the high-voltage load and quick-charge harness of the whole vehicle through the high-voltage electrical interface, including the pre-charge circuit, total positive relay, total negative relay, quick-charge relay, etc., controlled by the main board;

4. High-voltage control board: it can be integrated into the main board or independent, and can monitor the voltage and current of the battery pack in real time. It also includes pre-charge detection and insulation detection functions.

Main functions of BMS

1. Real-time communication: During the working process of the battery, the battery voltage, temperature, working current, battery power and other battery related parameters are monitored or calculated in real time.

2. Protection function: judge the current battery status according to the read battery working status and parameters, so as to carry out corresponding protection operation to prevent overcharge or overcharge of the battery.

3. Voltage and temperature detection: collect the voltage and temperature values of a single cell through the measurement sensor inside the BMS.

4. Charge and discharge management: set the best charge or discharge curve of the battery according to the collected voltage and temperature and different working conditions through the charge and discharge strategy

5. Balance management: according to the balance strategy, the battery power with poor consistency is pulled to the same level by means of power transfer or direct release of electrical energy through resistance.

6. SOC calculation: The voltage method calculates SOC according to the voltage-capacity model of lithium battery SOC.

7. Other functions

The BMS automatic test system developed and produced by Ruijie Instruments is built with self-developed instruments, which is convenient for integration and fast communication, and provides one-stop solutions for BMS manufacturers and application manufacturers. Welcome to call 4008-515-616 for consultation.

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