Battery Management

A battery management system (BMS) keeps track of a battery's condition and removes individual battery cell performance variances so that the cells operate consistently. It is a crucial system that enables the battery to operate at its best. The system, which is integrated into an electric vehicle (EV) that uses a large-capacity lithium ion battery, is crucial to prolonging the battery's lifespan and guaranteeing its safe operation. In addition to introducing the electronic components that make up the BMS, this article will go over the system configuration and functions of the BMS.

Table of Contents

• What is a Battery Management System?
• Battery management system for Electric vehicle
• Battery management system block diagram
• Battery Management System Components
• How Does a Battery Management System Work?
• Types of Battery Management Systems
• The Importance of Battery Management Systems
• Conclusion

What is a Battery Management System?

An assembly of battery cells electrically arranged in a row x column matrix configuration to enable the delivery of a targeted range of voltage and current for a duration of time against expected load scenarios is called a battery management system (BMS).

Battery management system for Electic vehicle

Long-term safe operation of a battery is made possible by a battery management system (BMS), which keeps an eye on and regulates the battery's condition. Every time a lithium ion battery used in an electric vehicle is charged or discharged, it deteriorates. The vehicle's performance may suffer as a result of these battery degradation cycles. One significant remedy for this issue is the BMS. It checks the state of the complete battery cells on a cell-by-cell basis and allows them to work evenly by reducing variances in individual batteries' performance. BMS in electric vehicles does these works:

Monitoring: Cell by cell, the BMS keeps an eye on the condition of every battery cell. Voltage measurement: To avoid overcharging or excessive discharging, the BMS measures the voltage of each battery cell or the battery pack as a whole.

Current measurement: The battery's discharge current or charge current is measured by the BMS. It performs appropriate control and determines whether the battery is charged or in use.

Measurement of temperature: Using a temperature sensor, the BMS continuously checks the battery's temperature. Longer service life and battery safety are guaranteed when the battery is used within the recommended temperature range.

Control: To enable consistent operation, the BMS removes individual battery cell performance variances.

Several battery cells make up a large-capacity battery pack. The performance and rate of deterioration of these cells vary. For instance, the entire performance or service life of the battery pack may be impacted if one cell degrades more quickly than the others. The function that eliminates such differences in performance or deterioration rate is known as "balancing."

Battery management system block diagram

The fundamental components of a BMS that prevents significant battery problems are shown in figure below:

Block Diagram of BMS
Source: www.mokoenergy.com

Cells connected in series can be handled by this sample BMS. This process, known as balancing (more on that later), involves a cell monitor reading the voltages of every cell and leveling them out. An MCU that manages telemetry data, switch manipulation, and balancing strategy is in charge of this.

The industry actually provides a variety of solutions for smaller designs, such as MCUs or single cells without balancing. The drawback of these more straightforward systems is that a designer cannot alter the functionality of the provided component (such as a high or low side switch).

A balancing mechanism is required when employing more cells. There exists basic schemes that can still operate without an MCU.

Battery Management System Components

Fuse: When a violent short circuit occurs, the battery cells need to be protected fast. A self control protector (SCP) fuse, which is mean to be blown by the overvoltage control IC in case of overvoltages.

Current Sensing/Coulomb Counting: Keeping a time reference and integrating the current over time, we obtain the total energy entered or exited the battery, implementing a Coulomb counter.

Thermistors

Temperature sensors, usually thermistors, are used both for temperature monitor and for safety intervention.

Main Switch

To act as switches, MOSFETs need their drain-source voltage to be Vds≤Vgs−Vth. The electric current in the linear region is Id=k⋅(Vgs−Vth)⋅Vds, making the resistance of the switch RMOS=1/[k⋅(Vgs−Vth)]. It's important to drive the Vgs accordingly to ensure low resistance and hence low losses. NMOS types are used also on high side switches through a charge pump, since normally they have lower RMOS.

Balancer

Battery cells have given tolerances in their capacity and impedance. So, over cycles, a charge difference can accumulate among cells in series. If a weaker set of cells has less capacity, it will charge faster compared to others in series.

How Does a Battery Management System Work?

The size, cost, and complexity of the battery pack, as well as its intended use and safety regulations and government certification requirements, all influence the Battery Management System's (BMS) design. Protection management and capacity management are two fundamental tasks that are always necessary, regardless of differences. Protection management, which includes both electrical and thermal protection, makes ensuring the battery runs within its Safe Operating Area (SOA).

Electrical protection: It is keeping an eye on voltage and current to avoid dangerous short-term surges, deep discharge, or overcharging. A BMS, for instance, permits brief peaks (such as during EV acceleration) but restricts continuous charging or discharging current without endangering cells. By lowering charge close to the upper threshold or decreasing load as it approaches the lower threshold, it also maintains each cell within acceptable voltage limits.

Thermal Protection: Thermal protection uses heating and cooling techniques to keep cell temperature within safe levels. Lithium plating is at danger while charging below 0 °C, and performance loss and accelerated aging can result from continual cycling at high temperatures. To maintain cells within their ideal range, a BMS uses active liquid cooling systems, fans, or passive airflow.

Capacity Management: It deals with battery pack cell imbalance. Because of aging, cycling, and self-discharge, cells deteriorate in diverse ways throughout time. Weaker cells reduce the useful capacity of the entire pack if they are not controlled. The BMS fixes this by balancing the state of charge (SOC) across cells. This can be done either actively, which redistributes energy among cells, or passively, which dumps excess charge from stronger cells. By ensuring that each cell contributes evenly, battery life is increased and performance is maintained.

To put it briefly, in demanding applications like electric vehicles, a well-designed BMS integrates temperature management, electrical protection, and capacity balancing to preserve the battery, optimize useable energy, and guarantee long-term dependability.

Types of Battery Management Systems

The topology of these systems, which refers to how they are mounted and function on the cells or modules across the battery pack, can be used to classify them.

Centralized BMS Architecture: It consists of a single central BMS for the battery pack. Every battery package has a direct connection to the central BMS.

Modular BMS Topology: The BMS is separated into multiple duplicate modules, each with its own bundle of wires and connections to a neighboring allocated section of a battery stack, much like a centralized implementation.

Primary/Subordinate BMS: Though conceptually similar to the modular topology, the master is responsible for processing, control, and external communication, while the slaves are more limited to just relaying measurement information.

Distributed BMS Architecture : All of the electronic components of a distributed BMS are mounted on a control board that is situated directly on the cell or module under observation.

The Importance of Battery Management Systems

A BMS's functional safety is its most crucial component. Preventing the voltage, current, and temperature of each cell or module under supervisory control from rising above specified SOA limits is crucial during charging and discharging operations. In addition to compromising a potentially costly battery pack, exceeding restrictions for an extended period of time may result in hazardous thermal runaway circumstances. Additionally, lower voltage threshold limits are closely watched for both functional safety and lithium-ion cell protection. Copper dendrites may eventually form on the anode of the Li-ion battery if it remains in this low-voltage state. This could lead to increased rates of self-discharge and potential safety issues.

Because lithium-ion powered devices have a high energy density, there is limited margin for mistake in battery management. BMSs and advancements in lithium-ion technology have made this one of the safest and most effective battery chemistries on the market today.

The battery pack's performance, which includes thermal and electrical management, is the next most crucial aspect of a BMS. All of the cells in the pack must be balanced in order to electrically maximize the total battery capacity, which suggests that the SOC of neighboring cells in the assembly is roughly equal. This is particularly crucial since it not only helps achieve the best possible battery capacity but also lessens the possibility of hotspots overcharging weak cells and preventing general degradation. The benefits of BMSs are at a glance:

• Safe-functionality
• Reliable, better life span.
• Satisfactory Performance
• Minimized Cost
• Ensures user awareness

Conclusion

One crucial system that keeps an eye on and regulates the battery's condition is the BMS. By using this feature, the BMS maximizes battery performance while maintaining battery safety. It is anticipated that an increasing number of BMSs will be integrated into EVs as EV production increases. Additionally, the market for motors with high power output, huge power capacity, and quick charging times is expanding. The electronic parts of the BMS must possess the following qualities in order to satisfy these demands: "high power," "high resistance to heat," and "high precision (temperature/voltage control)."