Analysis of Automotive Power Battery Management System

Analysis of Automotive Power Battery Management System

The Battery Management System (BMS) has become a hot spot with the increasing use of lithium batteries in different industries and products. This article focuses on its application in electric vehicles, focusing on the role, architecture and design considerations of BMS.

In the Chinese electric vehicle standard, there is a recommended national standard “Technical Conditions for Battery Management Systems for Electric Vehicles”. This standard defines a number of BMS functional requirements, divided into general requirements and technical requirements. The general requirements include battery data collection, information transmission and security management, including the detection of battery-related data related to heat and electricity (voltage, current and temperature parameters); real-time estimation of state of charge (SOC); Fault diagnosis, including fault handling mechanism; information exchange with other controllers of the vehicle through the bus; control and management of the charging process through communication with the charging device. Technical requirements include insulation resistance, insulation withstand voltage performance, battery system condition monitoring, SOC estimation, battery fault diagnosis, safety protection, and operating conditions including overvoltage operation, undervoltage operation, high temperature operation, low temperature operation, high temperature resistance, Low temperature resistance, salt spray resistance, damp heat resistance, vibration resistance, power polarity reverse resistance and electromagnetic radiation immunity.

The above standard definition may have some ambiguity about the concept of BMS, and the other may be more precise:

1. Monitoring: BMS monitors battery cells and battery packs by detecting physical parameters in the battery pack. Since the general battery pack requires a thermal system, flow is an important parameter; the state of charge (SOC) and battery health (SOH) should theoretically be placed in the monitored content, although it is desirable to derive both states. Need more data and computing support.

2. Calculation: The real calculation is actually the battery usage limit based on the state obtained by the vehicle controller. For example, under different SOCs, different limits of the maximum charging power and discharging power of the battery. Electric vehicles need to calculate and count battery usage, and need to count the energy used in a single use, the total energy used after first use, and the time after first use to assess the vehicle's electric mileage and battery life.

3. Communication: Both the BMS and the outside need to send data by means of communication. The battery and vehicle data are aggregated in a wireless and wired manner, which is a basic requirement for BMS communication. In the field of electric vehicle charging, DC fast charging, vehicle and grid power exchange (V2G), and vehicle and residential power exchange (V2H), in these future extended functions, BMS communication functions play a vital role.

4. Protection: In this section, it covers both fault diagnosis and processing, including overvoltage, undervoltage, overcurrent, low temperature, high temperature and short circuit. This part of the content has been a basic part of the BMS, but it is very relevant to the characteristics of the battery cell. In the case of fault handling, the BMS is often required to configure the switch and cooling system, but the important point is to balance the safety of the battery with the safety of the vehicle. If the BMS suddenly performs some operations without considering car safety, it will bring very bad results.

5. Optimization: This content covers battery pack balancing, battery capacity calculations, and other life optimization. After the car is used from the factory, with the increase of the number of charging times and the prolonging of the use time, it is an important task of the BMS to analyze the state of the battery through a series of parameter timings.

Of course, in the BMS, it may be necessary to add high-voltage interlocking, insulation testing or other functions due to the safety requirements of the entire electric vehicle. This part can be considered as a safety feature common to all high-voltage related components, and can be listed separately. 4 R. ^* \9 D& i3 Z0 ?6 H

A typical BMS system can be divided into an internal architecture and an external architecture.

Can be divided into:

1. Signal conditioning: cell voltage, module voltage, battery voltage, current and temperature sensors, flow sensors, insulation detection and other signal conditioning circuits, usually located on the sub-module and the main module.

2. Control drive part: control part of positive relay, negative relay, heating device drive, heat sink drive and high voltage interlock.

3. Generally only controlled by the main module.

4. Power and Clock Section: Due to the high voltage and 12V low voltage of the BMS, it is necessary to pay attention to the isolation problem first.

5. Processing part: This piece is basically the work of controlling strategies and algorithms.

7 can be divided into the following three parts:

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1. Mechanical connection: BMS can be distributed or centralized depending on the number and arrangement of battery cells. This will involve fixed issues with the main module and submodules. The mechanical connection problem of the entire battery pack system is often the key consideration of the design of electric vehicles, the analysis of force and vibration, and the quality configuration such as climbing, etc. are also considered.

2. Data communication: This refers to the actual bus interface, generally based on high speed and low speed CAN. In the future implementation of the smart grid system, wired interfaces such as power line carrier communication (PLC) and wireless interfaces such as Zigbee may be configured; in the battery pack designed by the national grid, GPS and other circuit modules are also arranged. '

3. Physical connection: The voltage on the positive and negative terminals of the single cell, the temperature measuring sensor and the current sensor need to be directly connected to the BMS. This part is a seemingly simple but intelligent place.

The external architecture is the cornerstone of the BMS's work with battery systems and other components.

Due to the traditional driver's habits, HEV, PHEV, EREV and EV are designed according to the basic requirements of ordinary cars, so that the improved power system and basic driving situation need to be larger with the original internal combustion engine. Similarity. With the European NEDC, ECE 15, EUDC, US FTP72, FTP 75, SFTP, US06, SFTP, SC03 and Japan 10-15 Mode as the driving conditions, the actual working condition of the battery pack can be obtained through the whole vehicle. In many laboratories, data from such a vehicle test platform can be seen, and the actual working environment of the BMS is based on these abstracted typical conditions.

A very important factor that distinguishes an electric vehicle from other electrical equipment is that it requires both high power and large energy. High power means high current, which means that it is difficult to accurately measure current at low cost. The high energy means that the battery capacity and quantity are huge, both of which have high safety requirements for the battery pack. Under the combination of a series of factors, there are many things involved in car BMS. Here are some of the personal opinions, I hope to discuss this field with you.

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