Introduction
Lithium-ion battery packs for electric vehicles have large battery capacity, many series and parallel connections, complex systems, and high-performance requirements such as safety, durability, and power. In addition, the safe working area of the lithium-ion battery pack (Function and Components of Battery Pack) is limited by temperature and voltage. If it exceeds the allowable range, the performance of the battery pack will accelerate decay, and even safety problems may occur.
The figure below shows the electrical connection topology of the whole vehicle. The part we care about is the part of the blue dotted line in the figure below
1. The Composition of the Battery Pack:
A battery pack includes a battery pack case, a battery pack connected in series and parallel, a battery management system (BMS), a wiring harness (strong & weak current), strong current components (relays, resistors, fuses, Hall sensors), etc.
2. Why are Pre-Charge Relays and Pre-Charge Resistors Added to the Battery Pack Components:
This question needs to first understand the bus capacitance of the new energy vehicle:
In the motor controller, the DC power of the battery pack is used as the input power supply, which needs to be connected to the motor controller through the DC bus. This method is called DC- LINK or DC support, and the capacitors are called bus capacitors or support capacitors or DC-Link. capacitance. Since the motor controller obtains a pulse current with a high RMS value or a high peak value from the battery pack, it will generate a high pulse voltage on the DC support, which makes the motor controller unbearable, so it is necessary to select a bus capacitor for connection.
In the pre-charging process, the main positive relay is disconnected first, and the pre-charging circuit formed by the pre-charging relay and the pre- charging resistor is connected first. Assume that the resistance value of the pre-charging resistor is above 30Ω, and the loop voltage is assumed to be 300 V. At this time, the maximum loop current is also Just 10A, the capacity of the pre-charge relay is above 10A, and the pre-charge circuit is safe.
Therefore, the function of the pre-charge relay is to control the opening and closing of the pre-charge circuit, and the function of the pre-charge resistor is to limit the current.
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3. Hall Sensor
Generally, the negative side of the circuit is used to measure the charge and discharge current value of the entire circuit.
4. BMS (Battery Management System)
There are two types of BMS: integrated type and discrete type. The discrete type is mainly divided into three modules, the main control module (BCU), the slave control module (BMU) and the insulation monitoring module (HVU). The discrete system architecture diagram is as follows:
Components Of BMS
Main Functions of BMS
BCU (main control module): Receive and comprehensively judge the basic information of the battery, calculate the SOC, upload or send control commands, carry out external relay control, vehicle CAN communication, charging CAN communication, intranet CAN communication, data storage, input and output signals Detection, charging and discharging current acquisition;
BMU (battery information monitoring module, slave module): Single battery voltage acquisition, battery temperature acquisition, battery balance management, single box battery thermal management, intranet CAN communication;
HVU (insulation monitoring module): Battery pack insulation monitoring, battery pack total voltage monitoring, motor controller pre-charge voltage detection, intranet CAN communication;
Conclusion
Therefore, the battery management system is indispensable and extremely important. On the one hand, the battery management system needs to detect, collect and initially calculate the real-time battery status parameters, and control the on and off of the power supply loop based on the comparison between the detected value and the allowable value; on the other hand, the battery management system needs to report the collected key data to the whole The vehicle controller, and receives the instructions of the controller, and coordinates with other systems on the electric vehicle.
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