The working principle of the battery management system bms, a component of the battery management system

2021-09-11 08:51:09 0

Battery management system concept

The battery management system, BMS (Battery Management System), is an important component of the power battery system of electric vehicles. On the one hand, it detects, collects and preliminarily calculates the real-time battery status parameters, and controls 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, it reports the collected key data to the vehicle controller and receives the controller To coordinate with other systems on the vehicle. Battery management system, different battery types, often have different requirements for the management system.

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Battery management system function

Generally speaking, the electric vehicle battery management system should realize the following functions:

1. Accurately estimate the state of charge of the power battery pack:

Accurately estimate the state of charge (StateofCharge, or SOC) of the power battery pack, that is, the remaining battery power, to ensure that the SOC is maintained within a reasonable range, and to prevent damage to the battery due to overcharge or overdischarge, so as to predict the hybrid electric vehicle storage at any time How much energy is left in the energy battery or the state of charge of the energy storage battery.

2. Dynamically monitor the working status of the power battery pack:

In the process of battery charging and discharging, real-time collection of the terminal voltage and temperature of each battery in the battery pack of the electric vehicle (should be a power battery pack), charging and discharging current and the total voltage of the battery pack, to prevent the battery from overcharging or overdischarging. . At the same time, the battery status can be given in time, the problematic battery can be selected, and the reliability and efficiency of the entire battery group can be maintained, making the realization of the remaining power estimation model possible. In addition, it is necessary to establish a history file of each battery to provide information for further optimization and development of new types of electricity, chargers, motors, etc., and to provide a basis for offline analysis of system failures.

3. Balance between single cells and battery packs:

is the balance between the single cell and the battery pack, so that each battery in the battery pack reaches a balanced state. Battery balancing is generally divided into active balancing and passive balancing. Most of the BMSs that have been put on the market currently use passive equilibrium. Equalization technology is the key technology of a battery energy management system that is currently being researched and developed in the world.

Principles of Battery Management System

The battery management system (BMS) determines the status of the entire battery system by detecting the status of each single battery in the power battery pack, and performs corresponding control adjustments and strategy implementations on the power battery system according to their status to realize the power battery system And the charge and discharge management of each monomer to ensure the safe and stable operation of the power battery system.

Typical battery management system topology diagram structure is mainly divided into two major parts: master control module and slave control module. Specifically, it is composed of a central processing unit (main control module), a data acquisition module, a data detection module, a display unit module, and a control component (fuse device, relay), etc. Generally, the data information communication between the modules is realized by using the internal CAN bus technology.

Based on the functions of each module, BMS can detect the voltage, current, temperature and other parameters of the power battery in real time, realize the thermal management, balance management, high voltage and insulation detection of the power battery, and can calculate the remaining capacity of the power battery, charge and discharge power, and SOC&SOH status.

The main components of the battery management system

1. Battery terminal module: mainly for data collection, such as: voltage parameters, current parameters, temperature, communication signals, etc.

2. Intermediate control module: mainly communicate with the vehicle system, control the charger, etc.

3. Display module: Mainly carry out data presentation and realize human-computer interaction

In order to meet the relevant standards or specifications, these components of the BMS must complete the following tasks:

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), insulation detection (monitoring leakage), collision detection, etc.;

2. Battery status 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, reduced insulation, etc.;

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. Damage to battery and human body caused by current, leakage, etc.;

5. Charge 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. The battery is balanced. 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 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, the BMS is inconvenient to disassemble on the vehicle, and it needs to be online calibration, monitoring, upgrade and maintenance without removing the shell. The general vehicle network adopts CAN;

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.;

10. Electromagnetic compatibility. Due to the harsh environment, the BMS is required to have good anti-electromagnetic interference capability, and at the same time, the BMS is required to have low external radiation.