Battery management system definition
Battery management system definition
The main task of the battery management system is to ensure the design performance of the battery system, which can be decomposed into the following three aspects:
1) Safety, to protect battery cells or battery packs from damage and prevent safety accidents;
2) Durability, so that the battery works in a reliable and safe area, and prolongs the service life of the battery;
3) Power, to maintain the battery working in a state that meets the requirements of the vehicle.
BMS is composed of various sensors, actuators, controllers and signal lines. In order to meet relevant standards or specifications, BMS should have the following functions.
1) Battery parameter detection. Including total voltage, total current, single battery voltage detection (to prevent overcharge, overdischarge and even reverse polarity), temperature detection (preferably each string of batteries, key cable joints, etc. have temperature sensors), smoke detection (monitoring electrolysis Liquid leakage, etc.), insulation detection (monitoring leakage), collision detection, etc.
2) Battery state estimation. Including state of charge (SOC) or depth of discharge (DOD), state of health (SOH), state of function (SOF), state of energy (SOE), fault and safety state (SOS), etc.
3) Online fault diagnosis. Including fault detection, fault type judgment, fault location, fault information output, etc. Fault detection refers to the use of diagnostic algorithms to diagnose fault types through the collected sensor signals, and early warning. Battery failure refers to sensor failures and actuator failures (such as contactors, fans, pumps, heaters, etc.) of various subsystems such as battery packs, high-voltage electrical circuits, and thermal management, as well as network failures, and various controller software and hardware failures. Wait. The failure of the battery pack itself refers to overvoltage (overcharge), undervoltage (overdischarge), overcurrent, ultra-high temperature, internal short-circuit failure, loose joints, electrolyte leakage, and reduced insulation.
4) Battery safety control and alarm. Including thermal system control, high-voltage electric safety control. After BMS diagnoses the fault, it informs the vehicle controller through the network and requires the vehicle controller to perform effective processing (the BMS can also cut off the main circuit power supply when a certain threshold is exceeded) to prevent high temperature, low temperature, overcharge, overdischarge, and over discharge. Current, leakage, etc. damage the battery and human body.
5) Charging control. There is a charge management module in the BMS, which can control the charger to safely charge the battery according to the characteristics of the battery, the temperature level and the power level of the charger.
6) Battery balance. The inconsistency makes the capacity of the battery pack smaller than the capacity of the smallest cell in the pack. Battery balancing is based on the information of single cells, using active or passive, dissipative or non-dissipative balancing methods to make the capacity of the battery pack as close as possible to the capacity of the smallest single cell.
7) Thermal management. According to the temperature distribution information in the battery pack and the charging and discharging requirements, determine the intensity of active heating/dissipation, so that the battery can work at the most suitable temperature as much as possible, and give full play to the performance of the battery.
8) Network communication. The BMS needs to communicate with network nodes such as the vehicle controller; at the same time, it is not convenient to disassemble the BMS on the vehicle. It needs to be online calibration, monitoring, automatic code generation and online program download without disassembling the shell (program update without disassembling the product) ), etc., the general in-vehicle network adopts CAN bus technology.
9) Information storage. Used to store key data, such as SOC, SOH, SOF, SOE, accumulated charge and discharge Ah number, fault code and consistency, etc. The real BMS in the vehicle may only have some of the hardware and software mentioned above. Each battery unit should have at least one battery voltage sensor and one temperature sensor. For a battery system with dozens of batteries, there may be only one BMS controller, or even integrate the BMS function into the main controller of the vehicle. For a battery system with hundreds of battery cells, there may be a master controller and multiple slave controllers that manage only one battery module. For each battery module with dozens of battery cells, there may be some module circuit contactors and balancing modules, and the slave controller manages the battery modules like measuring voltage and current, controls the contactors, balances the battery cells and communicates with the master controller Communication. Based on the reported data, the main controller will perform battery state estimation, fault diagnosis, thermal management, etc.
10) Electromagnetic compatibility. Due to the harsh operating environment of electric vehicles, BMS is required to have good anti-electromagnetic interference capability, and at the same time, BMS is required to have low external radiation.