Role of Battery Management system in an EV

Battery Packs in EVs/HEVs:

• Consist of hundreds of cells, delivering around 400 V to power electric motors.

• Monitored and managed by a Battery Management System (BMS).

• Charged via an onboard AC/DC converter module, with charging voltages ranging from 110 V (single-phase) to 380 V (three-phase).

• Role of the BMS:

  • Extends battery lifespan and enhances vehicle range.

  • Tracks key metrics: State of Health (SoH), State of Charge (SoC), and Depth of Discharge (DoD).

  • Monitors individual cells to address capacity degradation over time.

  • Balances cells during charging and discharging to maintain uniformity.

• Challenges in Battery Packs:

  • Aging cells lose capacity, reducing the overall battery pack performance.

  • Variations in SoC, impedance, and capacity increase with the number of cells.

  • A single underperforming cell in a series stack can cause divergence in SoC over multiple cycles.

• Battery Monitoring and Protection:

  • Ensures optimal performance during charging and discharging.

  • Incorporates components for voltage/current measurement, signal isolation, and safety monitoring.

  • Critical for Li-ion battery packs, which are prone to catastrophic failures from overvoltage.

• Example: Texas Instruments’ BQ76PL536A:

  • Designed for Li-ion cell balancing and monitoring.

  • Stackable protector and analog front-end for 3 to 6 series cells per pack.

  • Features include a high-accuracy ADC, independent voltage/temperature protection, cell balancing, and a precision 5 V regulator.

  • Multiple devices can be stacked to monitor up to 192 cells without additional isolation components.

  • Protects against overcharge, overdischarge, and overtemperature, ensuring system safety.