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Brief introduction of Lithium battery BMS(Battery Management System)

BMS board

What is BMS(Battery management system)?

BMS is short for Battery Management System, commonly known as Battery nanny or Battery manager, is mainly used to intelligently manage and maintain each battery pack, prevent overcharging and overdischarging of the Battery pack, prolong whose service life, and monitor whose working status.

The whole BMS including the system, the control module, display module, wireless communication module,battery information collection module etc. BMS battery management system through the communication interface connected to the wireless communication module and display module. The output end of the collection module is connected with the input end of the BMS, the output end of the BMS is connected with the input end of the control module, the control module is respectively connected with the battery pack and appliances, and the BMS is connected with the Server through the wireless communication module.

Composition of BMS:

Battery management system and Lithium battery closely together, through the sensors to do the battery voltage, current, temperature, real-time detection, as well as detect the leakage of electricity, thermal management, battery balanced management, alarm to remind, calculation the state of capacity(SOC), discharge power, the report of the state of health of battery (SOH). It also uses algorithms to control the maximum output power according to the voltage, current and temperature of the battery to obtain the maximum using, and uses algorithms to control the charger to charge the best current. Through the CAN bus interface, it communicates with the vehicle master controller, motor controller, energy control system and vehicle display system in real time.

BMS consists of BMU master controller, CSC slave controller, CSU equalization module, HVU high voltage controller, BTU battery status indicator unit and GPS communication module. From small to master-slave integrated architecture of power tools, electric bikes, electric forklifts, intelligent robots, IOT smart home, light hybrid vehicles, master-slave separated electric vehicles (pure electric, plug-in hybrid), electric ships, and then to the three-tier architecture of energy storage system.

BMS Architecture diagram

1.The main board, as the brain of BMS, will collect sampling information from each slave board (usually called LCU), communicate with the vehicle through the low-voltage electrical interface, control the relay action in BDU (high voltage breaking box), implement the monitoring of various states of the battery, and ensure the safe use of the battery in the charging and discharging process;

2.Slave board (LCU), as the sentinel of BMS, monitors the information of monomer voltage and temperature of the battery module and transmits the information to the main board, which has the function of battery balancing. The communication mode between slave board and motherboard is usually CAN or Daisy chain communication;

3.BDU is the entrance gate of the battery pack electric energy. It is connected with the vehicle high voltage load and fast charging wiring harness through the high voltage electrical interface, including pre-charging circuit, total positive relay, total negative relay, fast charging relay, etc., controlled by the main board;

4.High voltage control board, the gate guard of the battery pack electric energy in and out, can be integrated in the main board, or can be independent, real-time monitoring of the voltage and current of the battery pack, but also contains precharge detection and insulation detection functions.

PCBA board

The above is mainly the composition and introduction of BMS hardware, another important part of BMS is the software system, mature BMS software development is usually based on AUTOSAR architecture development. AUTOSAR architecture divides ECU software running on Microcontroller into three layers: Application, RTE and BSW. Because software systems are relatively abstract and highly specialized, I won’t go into details here. Here’s an example to help you understand the software components of BMS:

Let’s assume that the process of building a BMS is similar to building a building (regardless of what the building is for). So, the BWS basic software layer is the foundation and underground infrastructure construction part of our building. For example, external power supply equipment, internal generator, machine room, monitoring room, warehouse, drainage system and so on… Infrastructure.

With this infrastructure and equipment, we can build the buildings we want on the ground and provide the basic conditions for the stable operation of the buildings. RTE operation environment refers to the main machine room and main power distribution room of the building, and some basic operation communication equipment, including electrical signals and network signals, all over the building, such as network cables, wires and ventilation. The Application layer is the final embodiment of what our building is used to do. If it is an OFFICE building, we will decorate it as office. If it is a research building, we will decorate it as a laboratory; If it’s just a bar, we can decorate it like a nightclub. So the popular explanation, the compilation of application layer software, is this “decoration” process, in order to achieve different functions, to develop different logic.

What are the functions of BMS?

The functions of the battery management system can be divided into measurement function, core algorithm and application function, as shown in the below picture:

BMS function diagram

In terms of the function of BMS, the length would be endless if we go into details. Therefore, we will give a general introduction and have a systematic understanding.

There are roughly three large functional modules in BMS.

First, the measurement function mainly includes: voltage sampling and temperature sampling of the module, total voltage sampling and total current sampling of Pack, high voltage interlock detection, insulation detection. The measurement function monitors the basic state of the battery in real time and is the basis of all functions of BMS. Without these measurements, all core algorithms and application functions of BMS are difficult to execute.

Second, the core algorithm mainly includes: SOC (battery state) algorithm, SOH (life state) algorithm, SOP (power state) algorithm, battery equalization algorithm. Someone who like to challenge algorithms can challenge. Among them, SOC algorithm, typical schemes in the industry include ampere-hour integral, open circuit voltage, artificial neural network and Kalman filter. A single scheme will have shortcomings. At present, the mainstream scheme is to use ampere-hour integral plus Kalman filter. SOH algorithm, currently commonly used algorithms are coulomb algorithm plus open circuit voltage, and Kalman filtering algorithm and so on. SOP algorithm, the current reliable method or rely on the test data, with table lookup method to achieve. The principle of balance function, can associate with “Cannikin Law”, there are active balance and passive balance two methods. Active equalization is the cutting of long boards to complement the short boards, so that all boards are equal; Passive equilibrium means that all the long boards are cut so that all the long boards are as long as the shortest one.

Third, the application functions mainly include: high voltage and low voltage power on and off, AC charging and DC charging, battery system thermal management, battery system fault diagnosis. Among them, the high-voltage and low-voltage power-on and power-off need the cooperation of other controllers, such as VCU and BMS. BMS can supply power or charge the high-voltage load of the vehicle only after the high-voltage power-on is completed (BMS can handle the power-on and power-off process by itself if it is made by manufacturers with high integration). Ac charging is to charge the power battery by AC charging pile and vehicle charging machine. DC charging is to charge the power battery through the DC charging pile. Charging function has relevant national standards. The purpose of battery thermal management is to ensure that the battery is in a reasonable temperature range and the charge and discharge function is in the best state. Fault diagnosis, the content is more, the safety of the battery depends on this, including over voltage protection, over current protection, relay adhesion detection, battery differential pressure protection and so on.

BMS installed inside of Lithium power battery pack

Who are the mainstream BMS manufacturers in China?

As an important link between battery pack, vehicle system and motor, BMS is the core technology of Lithium battery pack and the most important index to measure the performance of a pure electric vehicle.

The complexity of BMS system itself determines that it has strong technical barriers and requires time for technical research and development. Its cost accounts for about 5-20% of the total cost of battery pack.

China’s BMS enterprises can be divided into several types: battery factory concurrently, vehicle factory concurrently and BMS manufacturers.

At present, the first echelon of lithium battery enterprises in China are: CATL, CALB, Gotion, Microvast, etc., because they produce lithium battery cells themselves, the final application needs to be assembled into a complete lithium battery pack. Therefore, more and more downstream customers want to get the battery pack that can be directly applied from the battery factory. Therefore, powerful battery factories begin to establish their own BMS R&D teams or acquire other BMS companies to achieve expansion and improve their competitiveness. However, because lithium batteries are in short supply in the global market, large battery factories currently implement the development strategy of “grasping the big and releasing the small” and only focus on customers with large volume or high growth potential customer in the future. Therefore, limited BMS resources are also fully serving these customers, and basically do not open to the market.

Represented by BYD, BAIC New Energy and ZTO Bus, the BMS for lithium battery developed by them are basically limited to the use of their own vehicles, highly concentrated on passenger cars and commercial vehicles. Although there are huge advantages in cost and high level of technology, the choice of application fields is very narrow. It can not meet the functions and requirements of various lithium battery applications in the market.

BMS installed inside of small cylidrical lithium battery pack

BMS’s professional and self-operated representative enterprises are shenzhen Jibaida,whose website is:http://www.jiabaida.com/, Udan Technology,http://www.udantech.com/#/, Hunan Xiaobu Technology http://www.center-iot.com/en/index.html and so on Enterprise. Among them, Jiabaida is involved in a wide range of fields, from solar street lamp BMS supporting low current to BMS of engineering machinery vehicles requiring high current discharge management, while Udan focuses on the application of engineering vehicles and develops network communication modules such as SaaS, 4G and 5G, with higher technological content. Hunan Xiaobu focuses on low-speed vehicle lithium battery BMS and energy storage. Each has his own preference and expertise, and deeply cultivates the application of niche fields.

CeramiX has business ties with most of these companies to develop lithium pack integrations and serve overseas customers. Customers can contact these BMS companies directly, or they can send their requirements and solutions to CeramiX, and we will act as your window to mobilize upstream and downstream resources to provide you with a total solution for lithium battery applications.

At the end of this article, I recommend Battery Management Systems for Large Lithium Ion Battery Packs by Davide Andrea for those interested in connectivity.

https://books.google.com/books/about/Battery_Management_Systems_for_Large_Lit.html?id=o-QpFOR0PTcC

In addition, there is a popular science video on BMS to help you understand the basics of BMS faster.

https://training.ti.com/battery-safety-and-protection-overview?context=1134734-1139260-1127704

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Tommy Zhao
Tommy Zhao
COO of CeramiX. Tommy has held senior executive positions including sales Director of GTM Group and General Manager of Ningbo Source E-business Co., LTD. He has traveled to more than 30 countries around the world. With 15 years of foreign trade sales and management experience, He has a deep understanding of lithium battery production and application.
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