Balancing Control Strategies in BMS

In balancing management, the BMS flexibly selects appropriate control strategies based on the actual conditions and requirements of the battery pack. These strategies may vary depending on battery type, operating environment, and management objectives.

1. Terminal Voltage-Based Balancing Strategy

• Balances cells based on their terminal voltage, using it as the consistency criterion.

  • Overvoltage cells: Discharge excess voltage.

  • Undervoltage cells: Charge to raise voltage.

• Advantage: Simple implementation.

• Limitation: Susceptible to internal parameter variations (e.g., internal resistance, temperature).

2. Capacity-Based Balancing Strategy

• Balances cells by optimizing the capacity utilization rate of the entire pack.

  • Maximizes overall capacity but is unsuitable for dynamic balancing (e.g., during rapid charging/discharging).

3. State of Charge (SOC)-Based Balancing Strategy

• Uses SOC as the balancing criterion.

  • Similar to capacity-based strategies but focuses on SOC measurements.

  • Advantage: Practical and efficient, as it only requires SOC tracking without detailed capacity data.

4. Balancing Modes: Passive vs. Active

Passive Balancing (Energy-Dissipative Balancing)

• Principle: Parallel resistors are connected to cells. Excess energy from fully charged cells is dissipated as heat via resistors.

• Advantages: Simple circuitry, low cost.

• Disadvantages: Low energy efficiency, increased thermal load.

• Implementation: Resistor-based algorithms discharge high-voltage cells to match others.

Active Balancing (Energy-Transfer Balancing)

• Principle: Transfers energy between cells using circuits (e.g., inductors, capacitors, or DC-DC converters).

  • Inductor-based: Uses inductors as energy storage elements with switch control.

  • Bidirectional DC-DC: Adjusts input/output voltages for precise energy transfer.

  • Charging-based: Charges low-voltage cells individually via DC/DC modules.

• Advantages: High energy efficiency, optimal energy distribution.

• Disadvantages: Complex circuitry, higher cost.

5. Strategy Selection Guidelines

• Passive Balancing: Suitable for cost-sensitive applications with lower energy efficiency requirements.

• Active Balancing: Ideal for high-performance systems demanding energy efficiency and extended battery life.

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6. Implementation Considerations

• Battery Characteristics: Chemistry, aging, and capacity variations.

• Operating Environment: Temperature, charge/discharge rates.

• User Requirements: Cost, efficiency, and safety priorities.

In summary, balancing control is critical for ensuring battery pack safety, stability, and longevity. The choice between passive and active balancing depends on trade-offs between cost, efficiency, and application-specific demands.