Basic Structure Of Battery Management System for Electric Vehicle

BMS can be classified based on hardware and software components. It consists of a data acquisition unit and a control unit, each playing a vital role in battery management. These components work together to ensure the battery operates within safe limits, optimizing performance and extending its usable life.

1. Hardware Components

Main Control Unit: Oversees the overall functioning of the battery system, collecting and processing critical data.

Sub-Control Unit: Manages individual battery modules, ensuring even distribution of power and proper balancing.

High Voltage Control Box & Insulation Box: Ensures safe operation in high-voltage environments by preventing electrical hazards.

Electronic Sensors: Collect voltage, current, and temperature data for real-time monitoring, enabling quick response to potential issues.

Relay and Switching Circuits: Facilitate the safe disconnection of the battery in case of faults, preventing damage to the system.

2. Software Components

Low-Level Software: Responsible for sensor data collection and processing, ensuring the reliability of real-time monitoring.

Application Layer Software: Communicates with the vehicle control unit and charger to manage charging and discharging processes, optimizing energy efficiency.

Machine Learning Algorithms ⇱: Some advanced BMS solutions incorporate AI-based analytics to predict battery health and optimize charging cycles.

–

Basic Functions of the EV Battery Management System (BMS)

The EV BMS (Battery Management System) achieves protection for the EV battery system against overvoltage, undervoltage, overcurrent, excessive high temperature, and excessively low temperature through voltage, current, and temperature detection. It also provides relay control, state of charge (SOC) ⇱ estimation, charge and discharge management, heating or insulation, balancing control, fault alarm and handling, communication with other controllers, and high-voltage circuit insulation detection. Additionally, the BMS includes a heating function for the EV battery system.

The BMS in the EV battery pack collects real-time data, including the voltage of each cell, temperature values from various sensors, the total voltage and current of the battery system, and the insulation resistance of the battery system. It determines whether the battery system is operating normally based on the preset threshold values and monitors faults in real-time. The EV battery system communicates with the vehicle controller or the motor using the CAN bus to perform charge and discharge management comprehensively.

From the perspective of the entire vehicle, the functions ⇱ and responsibilities of the Battery Management System (BMS) can be detailed as follows:

• Protecting individual cells and the entire EV battery pack from damage.
• Ensuring the battery operates within a suitable voltage and temperature range.
• Meeting the vehicle’s energy demands while keeping the battery in optimal conditions.
• Battery parameter detection, including total voltage, total current, cell voltage detection, temperature detection, insulation detection, collision detection, impedance detection, and smoke detection.
• Battery status estimation, including state of charge (SOC), state of power (SOP), and state of health (SOH).
• Online diagnostics, covering sensor faults, network faults, battery faults, battery overcharge, over-discharge, overcurrent, and insulation faults.
• Battery safety protection and alarms, including thermal control and high-voltage control. When a fault is diagnosed, the BMS reports it to the vehicle controller and charger while cutting off the high voltage to protect the battery from damage, including leakage protection.
• Charging control, managing both slow and fast charging.
• Battery consistency control, where the BMS collects individual cell voltage information and uses balancing strategies to ensure consistency. The balancing methods include dissipative and non-dissipative balancing.
• Thermal management, where the BMS collects temperature data at various points in the EV battery pack and determines whether to activate heating or cooling during charging and discharging.
• Networking functions, including calibration, health monitoring, and online program downloads, typically via a CAN network.
• Data storage, where the BMS stores critical information such as SOC, SOH, charge and discharge ampere-hours, and fault codes.

Working Principles of EV Battery Management System

A BMS operates through three main processes: charging, discharging, and heating during cold conditions. Each process is meticulously controlled to maximize efficiency and safety.

1. Charging Process

Pre-Charge Phase: After the onboard charger receives the charging gun insertion signal, it wakes up the vehicle controller and BMS. The BMS then performs an initial check and initialization, and upon completion, it reports to the vehicle controller. The vehicle controller controls the closure of the main negative relay, while the BMS also controls the main negative relay closure. The individual battery cells undergo pre-charging, and once it is confirmed that there is no short circuit in any cell, the pre-charging process is completed. The pre-charging process at the initial stage of charging is shown in the diagram below.

Slow charging process: Charging station → on-board charger → high-voltage control box → high-voltage connector → pre-charge relay  → pre-charge resistor → battery pack positive terminal → main fuse → battery pack negative terminal with current sensor → main negative relay → high-voltage connector  → high-voltage control box → on-board charger → charging station, forming a circuit for pre-charging.

Fast charging process: fast charging station → high-voltage control box → high-voltage connector → pre-charge relay → pre-charge resistor → battery pack positive terminal → main fuse → battery pack negative terminal → current sensor → main negative relay → high-voltage connector → high-voltage control box → fast charging station, forming a circuit for pre-charging.

Main Charging Phase: Once the initial checks pass, the BMS closes the main relay, allowing full current flow to the battery while monitoring for anomalies.

Slow charging process: Charging station → on-board charger → high-voltage control box → high-voltage connector → main positive relay → battery pack positive terminal → main fuse → battery pack negative terminal → current sensor → main negative relay → high-voltage connector → high-voltage control box → on-board charger → charging station, forming a circuit for slow charging.

Fast charging process: Fast charging charging station → high-voltage control box → high-voltage connector → main positive relay → battery pack positive terminal → main fuse → battery pack negative terminal → current sensor → main negative relay → high-voltage connector → high-voltage control box → fast charging charging station, forming a circuit for fast charging.

Trickle Charging Phase: As the battery approaches full charge, the BMS gradually reduces the charging current to prevent overcharging and heat buildup.

2. Discharging Process

Initial Discharge Phase: When the ignition switch is turned on, the BMS wakes up ⇱, conducts self-diagnostics, and then signals the main relays to close, allowing energy transfer to the vehicle.

Discharge initial pre-charge process: Battery pack negative terminal → main fuse → battery pack positive terminal with pre-charge resistor → pre-charge relay → high-voltage connector → high-voltage control box → main negative relay → current sensor → traction battery negative terminal, forming a circuit to complete pre-charge.

Main Discharge Phase: The BMS continues to regulate power delivery, ensuring optimal efficiency and safety under varying load conditions.

Discharge process: Battery pack negative terminal → main fuse → battery pack positive terminal → main positive relay → high-voltage connector → high-voltage control box → load (not shown in the diagram) → main negative relay → current sensor → traction battery negative terminal, forming a circuit to complete discharge.

Low Voltage Cutoff: To prevent deep discharge, the BMS disconnects the battery once a critical low voltage threshold is reached.

3. Cold Weather Charging & Heating

In low-temperature conditions, the BMS controls heating elements to maintain optimal battery performance and prevent energy losses due to cold weather.

If the battery temperature falls below a threshold, the system automatically initiates a pre-heating sequence before charging begins, ensuring efficiency.

Some systems use external heaters, while others employ self-heating battery cells to maintain an optimal operating temperature.

Understanding Battery Packs & BMS in Electric Vehicles

In electric vehicles, the lithium battery is the sole energy source that determines driving range. The typical EV battery system ⇱ includes the battery module, structural components, electrical system, thermal management system, and the BMS, each playing an integral role in vehicle performance.

1. Battery Modules

Battery modules consist of individual battery cells connected in series or parallel. For instance, the Geely EV450 has 17 modules with a total voltage of 346V, providing sufficient power for extended driving range.

2. BMS & Control Harness

The BMS continuously monitors the battery pack to ensure safe operation under different driving conditions.

It implements control strategies to optimize battery performance, lifespan, and cost-efficiency, reducing the need for frequent battery replacements.

3. Additional Components

Module Connection Wires: Facilitate communication and power distribution between cells, ensuring uniform current flow.

Cooling System: Maintains optimal battery temperature through liquid cooling or air-based thermal management.

High Voltage Components: Include relays, fast-charging plugs, and high-voltage connectors, ensuring reliable energy transfer.

Battery Enclosures: Protect the battery pack from environmental factors like moisture, dust, and mechanical damage.

Future Developments in BMS Technology

As battery technology advances, so does the role of BMS. Emerging innovations in BMS design include:

AI-Driven Predictive Maintenance: Using machine learning to analyze battery performance and predict potential failures.

Wireless BMS (wBMS): Eliminating the need for physical wiring, reducing weight, and improving modularity in EV battery packs.

Advanced Thermal Management: Integrating phase-change materials and active liquid cooling for better heat dissipation.

Bidirectional Charging Capabilities: Enabling vehicle-to-grid (V2G) applications where EV batteries can supply power back to the grid.

A well-designed BMS is essential for the safe and efficient operation of EV lithium battery ⇱. It not only protects individual cells but also enhances the overall performance and longevity of the battery pack. As electric vehicle technology advances, BMS capabilities will continue to evolve, offering smarter energy management solutions for a sustainable future. With further innovations, BMS technology will contribute to safer, longer-lasting, and more efficient battery systems in various applications beyond electric vehicles, including renewable energy storage and industrial power solutions.