What is Battery Management System (BMS)?

What is a battery management system?

Battery Management System (BMS) is a technology specifically used to monitor the working condition of the battery pack, commonly known as battery nanny or battery housekeeper, mainly for intelligent management and maintenance of each battery unit, to prevent the battery from charging and discharge, prolong the service life of the battery, monitor the state of the battery.

The BMS Battery management system is mainly composed of various sensors, actuators, controllers and signal lines. In order to enable new energy vehicles to drive safely on the road and meet the relevant standards and specifications, the BMS battery management system shall have the following functions monitoring the battery pack.

Not only Lithium battery, but also the future batteries, Solid State batteries and Sodium ion Batteries need BMS.

What is a Battery Management System? (Video from the Internet, in case of infringement, please contact to delete)

Learn more:

Battery Management System functions

Battery Parameter Detection

Monitor battery operating data, such as current, voltage, temperature, coolant flow (liquid-cooled battery), cell status, and balance data of each cell. Including total voltage, total current, single battery voltage detection (to prevent overcharging,over-discharge and even reverse pole phenomenon), temperature detection (best each string of battery, key cable joints all have temperature sensors), smoke detection (monitoring electrolyte leakage, etc.), insulation detection.

Battery Status Estimation

Calculate the operating status of the battery, maximum and minimum voltage, number of cycles, depth of discharge (DOD), state of health (SoH), safety state (SOS), maximum charging current (CCL), discharge current limit (DCL), internal resistance of the battery, Electricity cost [Ah] Delivery or storage, total running time, temperature detection, status of air cooling or liquid cooling, etc.

Online Troubleshooting

Including fault detection, fault type judgment, fault positioning, fault information output, etc. Fault detection refers to the diagnostic algorithm and early warning. Battery failure refers to the sensor failure, actuator failure (such as contactor, fan, pump, heater, etc.) of the battery pack, high voltage battery circuit, thermal management subsystem, network failure, various controller hardware and software failure, etc.

The fault of the battery pack itself refers to the over-voltage (overcharge), under-voltage (over-discharge), over-current, ultra-high temperature, internal short circuit fault, loose joint, battery electrolyte leakage, insulation reduction, etc.

Battery Management System

Battery Safety Control and Alarm

Including thermal system control, high-voltage electric safety control. After BMS Battery Management System diagnose the fault, notify the vehicle controller through the network, and require the vehicle controller to be effectively processed (BMS Battery Management System can also cut off the main circuit power after a certain threshold), to prevent high temperature, low temperature, overcharge, over-discharge, over-current, leakage and other damage to the battery and personal.

Charge Control

Battery Management System BMS has a charging management module, which can control the charger to charge the LiFePO4 battery safely according to the battery characteristics, the temperature level, and the power level of the charger.

Battery Equalization

The presence of the inconsistency makes the capacity of the battery pack smaller than the capacity of the smallest monomer in the group. Battery equalization is based on the single battery information, using active or passive, dissipated or dissipative or non-dissipative equilibrium methods, so as to make the battery pack capacity close to the minimum single capacity as far as possible.

Continuously optimize battery performance and actively balance the inconsistencies of each battery

Read more: How to make Lead Acid Battery equalization charge?

Heat Management

According to the temperature distribution information in the battery pack and the charge and discharge requirements, the strength of active heating / heat dissipation is determined, so that the battery works at the most suitable temperature as far as possible, and gives full play to the performance of the battery.

Battery Management System

Internetwork Communication

Such as reporting operating status to other devices through the communication protocol CAN, Battery Management System BMS needs to communicate with network nodes such as the vehicle controller; meanwhile, BMS is inconvenient to dismantle on the vehicle, including online calibration, monitoring, automatic code generation and online program download (updated without removing the product).

Storing of Information

To store key data, such as SOC, SOH, SOF, SOE, cumulative charge and discharge Ah number, fault codes, and consistency, etc. Real BMS in a vehicle may have only part of the hardware and software mentioned above. Each battery cell shall have at least one battery voltage sensor and one temperature sensor. For battery systems with dozens of batteries, there may be only one BMS controller, or even integrating the BMS functionality into the vehicle’s main controller. For battery systems with hundreds of battery cells, there may be a master controller and several subordinate controllers that manage only one battery module. For each battery module with dozens of battery cells, there may be some module circuit contactors and balance modules, and manage the battery module from the controller as if measuring voltage and current, control the contactors, balance the battery cell, and communicate with the main controller. Based on the reported data, the master controller will perform battery status estimation, fault diagnosis, thermal management, etc.

Electromagnetic Compatibility

Due to the harsh use environment of electric vehicles, BMS is required to have good anti-electromagnetic interference ability, while BMS is required to have small external radiation.

BMS management system as a new energy vehicle power battery pack monitoring management center, must be the battery temperature, voltage and charge and discharge current and other related parameters for real-time dynamic monitoring, when necessary, can take emergency measures to protect the monomer battery, avoid battery pack overcharged, excessive, high temperature and short circuit safety problems.

Energy Recovery

In electric vehicle systems, energy can be recovered to charge the battery.

BMS monitoring and control functions are for the entire battery pack, as well as for each cell in the battery pack. Lithium-ion batteries are currently the batteries with the highest energy density and are the first choice for everything from small electronic devices to electric vehicles to large energy storage systems. Although lithium batteries have excellent performance, their use is very strict and has a specified safe operating area (SOA) .

Why are Battery Management Systems so important?

Without BMS monitoring and control, the battery is prone to irreversible damage and even dangerous consequences. Therefore, the design of BMS is also very complex. The monitoring function ensures that the electrical, control, temperature, etc. conditions of the lithium battery are safe. Operate within the data range to prevent the voltage, current, and temperature of any battery or module monitored by the BMS from exceeding the safe operating area (SOA).

How does the battery management system work?

There is no fixed standard for battery management systems. The implementation of technical functions and design is usually related to the following factors:

  • Battery complexity, cost, size
  • Battery application safety issues, cycle times, warranty requirements
  • Government certification requirements of various countries, regulations on penalties for failure to meet safety requirements

BMS is designed with many functions, the most basic of which are battery protection management and capacity management. Among them, battery protection management allows the battery to work within the preset safe voltage and current range; it also has an overheating protection function and actively controls the temperature to maintain a good working environment for the battery.

Current protection

Monitoring the current and voltage of the battery pack is a basic function to protect the battery, because the safety of the battery is affected by current and voltage. Usually manufacturers preset the BMS to the normal operating range of current and voltage, which not only extends the battery life, but also prevents the battery from operating beyond the rated value to protect the battery.

Lithium-ion batteries usually have charging current limits and discharge current limits, which are protected from multiple angles such as charging and discharging usage time, current peak range, and instantaneous current limits. For example, in electric vehicles and energy storage power stations, the instantaneous maximum continuous current can be estimated. Outside the calculated protection range, the BMS system will trigger a reduction of the current or a complete interruption of the current.

safe voltage and current range

Voltage protection

The voltage of lithium batteries must also operate within a voltage range. The safe range of voltage is determined by the specific chemical properties and working environment of lithium batteries. Lithium batteries in a low-voltage state may grow copper dendrites on the anode, causing an increase in the battery’s self-discharge rate and causing safety issues. Low-voltage use may cause a memory effect of capacity loss in the lithium battery.

When performing large current loads or charging, the voltage is usually limited to optimize battery life. BMS must know all the situations that limit the battery voltage. In high voltage limit situations, it can reduce charging or terminate charging completely; when it is close to low voltage, it reduces the load. For example, when the battery voltage is low during the operation of an electric vehicle, BMS will Reduce the output traction torque of the motor to protect the battery.

Temperature management protection

BMS can regulate the temperature of the battery pack through heating or cooling. By configuring a heater and liquid cooling system to adjust the temperature of the battery to prevent excessively high or low temperatures, such as maintaining it at 30 to 35 degrees Celsius.

Although lithium-ion batteries have a wide operating temperature range, basically the capacity of lithium batteries operating at low temperatures will drop significantly, mainly because the chemical activity is reduced at low temperatures. Most lithium batteries cannot be charged quickly below 5 degrees Celsius. Charging is prohibited below 0 degrees Celsius. Although the low-temperature performance of lithium batteries is better than that of lead-acid batteries, temperature management is also very important, because low-temperature charging anode batteries will cause metal lithium plating, and vibration and pressure will cause damage to the internal structure of the battery, causing permanent damage to the battery.

Lithium battery safe temperature range

Capacity management

Maximizing battery capacity is an important feature of BMS. Without capacity management maintenance, battery packs will quickly become obsolete. The root of the problem is that the condition of each battery changes inconsistently. Batteries are connected in series and parallel to form a battery pack. The consistency of the batteries may be very different. For example, battery attenuation and self-discharge can cause deviations in the battery cells.

After battery inconsistency occurs, BMS can control and balance the capacity. For example, during the charging process, the fast-charging single battery will stop charging before reaching full power to prevent overcharging, and continue to charge the slow-charging battery. BMS will then It saves the inconsistent charge and discharge, prevents overcharge and overdischarge of some batteries, balances the overall SOC of the battery pack, and realizes the optimal capacity of the battery pack.

prevent lithium battery overcharging

Battery management system type

Centralized BMS architecture

All battery packs are connected to the central BMS, and there is only one BMS overall. Large batteries require a large number of link cables, making troubleshooting and maintenance generally burdensome.

Centralized BMS architecture

Modular BMS architecture

Multiple BMS are configured in the battery pack, one of which is the main module and supervises other BMS modules. This architecture has good scalability and is easier to maintain and troubleshoot, but the cost is relatively high.

Modular BMS architecture

Master/slave BMS architecture

Similar to the modular structure, this situation is that the master BMS is responsible for calculation, control, and communication, and the other slave BMS only has the function of relaying measurement information. This structure not only saves costs, but also simplifies the functions reasonably.

Masterslave BMS architecture

Distributed BMS architecture

All batteries are integrated with the BMS control board module. Each BMS handles calculations and communications independently. The structure seems simple. However, having a BMS for each battery is more expensive and complicates maintenance and troubleshooting.

Distributed BMS architecture

Summarize

The high energy density of lithium batteries makes the fault tolerance rate of BMS very small. The development of BMS and lithium-ion batteries has made chemically active lithium-ion batteries one of the safest batteries.

Leave a Reply

Your email address will not be published. Required fields are marked *