Composition and functions of new energy vehicle battery management BMS

火辣西米秀

Composition and functions of new energy vehicle battery management BMS [Copy link]

The main function of the electric vehicle BMS (Battery Management System) is to monitor, manage and protect the battery pack of the electric vehicle to ensure the safe, reliable and efficient operation of the battery.

1. Battery Management System Performance Parameters

1. BMS temperature range

1) Working temperature: -40℃—85℃

2) Storage temperature: -40℃—85℃

2. Battery pack temperature range

1) Charging operating temperature: -20℃—55℃

2) Discharge operating temperature: -30℃—55℃

3) Storage temperature: -40℃—65℃

3. Working voltage range

1) Normal operating voltage: 9V-16V

2) Inoperable voltage: lower than 6V or greater than 18V

3) CAN network operating voltage: 6V-18V

4) Test voltage: 13.5V±0.2V

5) Nominal voltage: 12V

6) Voltage tolerance range: ±0.2V

4. Working current

Peak current: 10A (maximum current for relay operation)

Maximum continuous operating current: ≤4A (main positive relay, main negative relay, fast charge relay, CSU, BMU)

Quiescent current: ≤0.5mA

2. Battery Management System Composition

There is a BMS in each battery pack PACK. BMS is generally composed of a CSC data acquisition system and a battery control unit.

1. CSC acquisition system

Each module has a CSC acquisition loop to monitor the voltage of each battery cell and the module temperature information, and report the battery cell voltage and module temperature information to the BMU.

2. Battery Control Unit (BMU)

Installed inside the power battery assembly, it is the core component of the battery management system. The battery control unit (BMU) is responsible for vehicle diagnosis, communication, calibration, charging control, collision monitoring, high-voltage interlocking, thermal management, balancing control, high-voltage sampling, high-voltage insulation monitoring, high-voltage relay drive, high-voltage relay diagnosis, high-voltage pre-charge control, management of CSC and BDU, calculation of SOC and SOH, management of battery status, application strategy, etc.

3. Battery Management System Function

1. Data collection and monitoring

BMS collects temperature detection, voltage detection, current detection, SOC estimation, SOH estimation and other parameters of the battery pack in real time to monitor the working status of the battery.

2. Battery status estimation

By analyzing the collected data, the BMS can estimate the battery's remaining charge (SOC), state of health (SOH) and other information, providing users with accurate battery status information.

3. Charge and discharge management

BMS controls the charging and discharging process of the battery to ensure that the battery operates within a safe range and prevent overcharging, over-discharging, etc.

4. Balanced management

In a battery pack, since the characteristics of each single battery cell may be different, the BMS will perform balancing management to ensure that each battery cell in the battery pack maintains the same voltage level during the charge and discharge process, helping to improve the performance, life and safety of the entire battery pack.

Balance control method: divided into active balance and passive balance. Active balance transfers energy from a cell with a higher voltage to a cell with a lower voltage through electronic components, which is a kind of energy transfer; passive balance consumes the energy of a cell with a high voltage or a high charge through a resistor, which is a kind of energy consumption.

Balancing circuit types: mainly include parallel balanced charging balancing, parallel switch charging balancing, energy transfer balancing and resistance parallel balancing.

5. Thermal management

The BMS monitors the temperature of the battery and takes appropriate measures to dissipate heat or heat the battery to maintain the battery within a suitable operating temperature range.

BMS temperature monitoring uses sensors to monitor the temperature of the battery in real time and transmits the temperature data to the BMS controller. The BMS controller will take corresponding measures based on the temperature data, such as starting the cooling system or reducing the battery charging power when the temperature is too high to prevent the battery from overheating and damage. The following are some common electric vehicle BMS temperature monitoring functions.

Temperature Sensor: BMS systems are usually equipped with multiple temperature sensors, which are distributed in different locations of the battery pack to accurately measure the temperature of the battery.

Real-time monitoring: BMS reads the temperature sensor data in real time and displays the temperature information on the dashboard or the display screen of the vehicle control system, so that the driver can understand the temperature status of the battery at any time.

Temperature warning: When the battery temperature exceeds the set safety range, the BMS will issue an alarm to remind the driver to take appropriate measures, such as stopping the car to cool down or avoiding excessive use of the battery.

Temperature control: BMS can automatically control the battery's charge and discharge process according to the temperature conditions. In a high temperature environment, BMS may reduce the charging power or stop charging to prevent the battery from overheating; in a low temperature environment, BMS may activate the heating function to increase the battery temperature to ensure normal charging and discharging.

Data analysis: BMS can also record historical data of battery temperature and analyze it to understand the working status and performance changes of the battery. This helps to discover potential problems and take corresponding maintenance measures.

6. Fault diagnosis and protection

BMS can detect fault conditions in the battery pack, such as overvoltage, undervoltage, overcurrent, short circuit, etc., and take timely protective measures to avoid battery damage or safety accidents.

7. Communication function

BMS communicates with other systems of the vehicle, transmits battery status information to the vehicle controller, etc., and provides CAN communication function and CAN network management function for comprehensive management and control.

8. Insulation testing

Insulation detection range:

(1) When all external contactors of the power battery are disconnected, the insulation detection range is the insulation information inside the battery pack. In this state, the external insulation of the battery pack cannot be detected;

(2) When in high voltage or discharge state, the insulation test range is the high voltage circuit of the whole vehicle, including the insulation performance of the battery pack and the high voltage circuit of the whole vehicle;

(3) In the fast charging state, the insulation test range is the high-voltage circuit of the whole vehicle and the high-voltage circuit of the fast charging, including the insulation performance of the battery pack, the high-voltage circuit of the whole vehicle, and the fast charging pile;

9. Pre-charge control

Pre-charging success judgment condition: The pre-charging is completed only when the difference between the external bus voltage and the total pack voltage is within 10V.

10. Release function

The discharge function means that when the IPU receives the power down command sent by the VCU and the positive and negative contactor disconnection command sent by the BMS, it has the function of discharging the internal capacitor energy of the motor controller in a short time to reduce the voltage to below 60V.

(1) Discharge begins when the vehicle is powered down, charging is completed, or smart charging is completed.

(2) The high-voltage contactor must be disconnected before discharge.

(3) Passive release is performed when active release fails.

(4) The active discharge function of the motor controller must be disconnected for 150ms after the main positive relay is disconnected;

(5) VCU sends a power down signal

13. Schedule charging

When BMS receives the reservation charging request sent by T-Box, it allows sending the reservation setting success status only when it detects that there is no fault affecting AC charging in itself and OBC. Otherwise, it sends the reservation setting failure status to T-Box.

When the scheduled charging time is reached, the BMS immediately wakes up the VCU and OBC via CAN. After the VCU wakes up, the IPU is immediately woken up via hardwire.

14. Intelligent power replenishment

(1) In the OFF position, the BMS allows the intelligent charging request to be sent only when it determines that the battery voltage is within the range of 10-12.3V.

(2) When the SOC is lower than 10%, it is not allowed to enter the intelligent charging process. When the SOC drops below 10% during the intelligent charging process, the BMS sends a message that the intelligent charging process is over.

(3) When the vehicle is in the OFF position, the BMS detects the battery voltage every once in a while, with the detection interval being 1.5 hours.

15. High voltage safety management function

(1) Collision power-off, high-voltage system circuit insulation and high-voltage interlock detection and processing, etc.

(2) The contactor control signal controlled by the BMS is short-circuited to the ground, short-circuited to the power supply, or short-circuited.

(3) Diagnose the main positive, main negative contactors, and fast charging contactors (pure electric) for adhesion and inability to close;