Embedded Systems and Design & Development - Feb 17, 2026 | Morning | VisionAstraa EV Academy

Embedded Systems for BMS — VisionAstraa EV Academy (Feb 17, 2026 — Morning)

Scope

• Lecture focused on battery management system (BMS) sensing, signal interfacing, ADC conversion, control logic and over-voltage protection for lithium‑ion batteries in EVs.
• Emphasis on practical sensor selection, safety‑driven design choices, and what an embedded controller needs to implement protection and control.

Key BMS functions covered

• Sense cell voltage, charge/discharge current, and temperature.
• Convert analog sensor outputs to digital (ADC), process in an embedded controller, and actuate switches to control/protect the battery.
• Typical system targets:
  • Cell-level: ≈ 3.1–4.1 V (nominal ≈ 3.7 V)
  • Pack / DC bus: ≈ 400 V (sometimes 800 V)
  • Onboard charger: AC (e.g., 3‑phase mains)
  • Auxiliary systems: 12 V or 48 V

Collect → process → control

Voltage sensing methods — types, pros/cons, and typical uses

1. Resistive potential divider

   • Simplest and cheapest way to step down DC/low‑frequency signals to ADC range (0–3.3 V or 0–5 V).
   • Widely used for auxiliary systems and some pack‑level measurements.
   • Limitations: loading, temperature coefficient, long‑term drift. Use automotive‑grade resistors for reliability.

2. Capacitive divider

   • Similar topology using capacitors; mainly suitable for high‑voltage AC measurement (not for DC).
   • Typical use: AC / onboard‑charger sensing.

3. Transformer / potential coil (voltage transformer)

   • Step‑down for AC only (relies on changing magnetic flux).
   • Good for onboard charger / AC mains measurements.
   • Output is bipolar AC — requires level shifting or rectification before ADC.

4. Hall‑effect sensors (including closed‑loop variants)

   • Common for current sensing; some closed‑loop designs or auxiliary coils can be used for voltage sensing.
   • Useful for DC bus and pack voltages; often combined with resistive dividers.
   • Provides galvanic isolation and good accuracy in automotive formats.

5. Opto‑isolator based sensing

   • Provides galvanic isolation.
   • Less common in EVs but usable where isolation is required.

6. Isolation amplifier / isolation ICs

   • Purpose‑built ICs that provide level shifting, scaling, noise filtering and galvanic isolation.
   • Common and recommended for safety‑critical measurements (e.g., pack / DC bus).
   • Example vendors: Texas Instruments (various isolation amplifier parts).

7. Dedicated battery‑monitoring ICs (cell monitors / CMS)

   • Application‑specific ICs that monitor many cell voltages, perform balancing, and interface to higher‑level BMS.
   • Common choice for per‑cell monitoring inside BMS modules.

Sensor selection guidance

• Rule out AC‑only sensors (capacitive dividers, potential transformers) for DC cell measurement.
• For single cell (≈ 3.1–4.1 V): candidate solutions include resistive dividers, isolation amplifiers, Hall‑based sensors, or dedicated cell‑monitor ICs.
• For battery pack / DC bus (≈ 400 V): prefer isolation amplifiers, Hall sensors (with dividers), or dedicated high‑voltage sensing ICs.
• For onboard charger (AC): capacitive dividers and potential transformers are relevant.
• For auxiliary low‑voltage systems: resistive dividers are often sufficient and cost‑effective.

Safety and standards

• ISO 26262 / Automotive Safety Integrity Levels (ASIL A–D) drive sensor and architecture choices:
  • Lower ASIL (A/B): resistive dividers might suffice.
  • Higher ASIL (C/D): require higher‑assurance solutions (isolation amplifiers, redundant / failsafe designs, dedicated ICs).
• For higher safety levels, design for redundancy and fail‑safe behavior; include mechanical and electrical protections.

Signal conditioning & interfacing

• Sensor outputs must be conditioned to match ADC input (scaling, offset/level shifting, filtering, and isolation as needed).
• Microcontroller ADCs typically accept 0–Vref (e.g., 0–3.3 V or 0–5 V) — high voltages must be stepped down.
• AC outputs require rectification, level shift, or an appropriate sampling strategy (e.g., convert bipolar to unipolar or sample half‑wave).

ADC considerations

Important ADC parameters:

• Resolution (bits): higher bits → better measurement resolution. Typical recommendation: 12–16 bit for battery pack monitoring.
• Conversion speed / throughput: trade‑off between resolution and sampling rate.
• Number of channels and simultaneous sampling needs.
• Input range (0–Vref): determines required scaling.

Notes and examples:

• ATmega328 ADC measures 0–Vcc and is limited in range/resolution for direct high‑voltage sensing; requires proper conditioning.
• Choose microcontroller peripherals (ADC, timers, interrupts, PWM, capture/QEP modules) according to application requirements.

Over‑voltage protection (charging)

• Typical control flow:
  • Voltage sensor → ADC → embedded controller → control output to semiconductor switch.
• Disconnect mechanism:
  • Semiconductor switches (MOSFETs / power transistors) to isolate cell/pack from charger when thresholds are exceeded.
• Protection layers:
  • Primary: controlled disconnect (MOSFET) via embedded decision.
  • Secondary: TVS (Transient Voltage Suppressor) diodes in parallel to clamp spikes/transients.
  • Last resort: fuses to physically isolate during catastrophic overcurrent.
• Charging thresholds and trade‑offs:
  • Higher charge voltage increases immediate capacity but reduces cycle life (example: charging to 4.3 V yields ≈100% capacity but far fewer cycles, versus charging to ≈3.9 V yields ≈50% capacity but much longer life).
  • Typical control: cut‑off around 4.1–4.2 V depending on chemistry and OEM recommendation; lower cut‑offs increase longevity.
• Emphasized importance of thermal and transient protection — lithium‑ion cells are sensitive to over‑voltage and temperature.

Design practices & tooling tips

• Use automotive‑grade components (resistors, sensors) to minimize drift over time and temperature.
• Use isolation amplifiers or opto/isolation solutions when galvanic isolation is required for safety.
• When extracting parameters from datasheets, consider using automated/generative tools to parse specs (ADC resolution, voltage ranges), but always cross‑verify results manually.
• Trade‑offs to consider: resolution vs. conversion speed vs. processing load.

Planned tutorials / hands‑on

• Afternoon session: demo implementing a simple over‑voltage protection circuit (microcontroller program + MOSFET disconnect) and introduction to current sensors (clamp / current‑transformer discussion).
• Practical objective: write code for an MCU to sample ADC, detect a 4.1 V cell voltage and command a MOSFET to disconnect the charger (demo‑level, not full automotive‑grade implementation).

References & examples mentioned

• ISO 26262 (ASIL A–D)
• ATmega328 microcontroller (ADC range and datasheet example)
• Texas Instruments isolation amplifier ICs (example modules)
• TVS diodes, fuses, MOSFETs (protection hardware)
• Cell nominal/threshold voltages: nominal ≈ 3.7 V, charge upper limit commonly 4.1–4.2 V, discharge cut‑offs vary

Main speaker / sources

• Instructor from VisionAstraa EV Academy (embedded systems / BMS course). Specific instructor name not given in the subtitles.
• Cited standards and vendors: ISO 26262, ATmega328 (AVR), Texas Instruments isolation amplifier parts; general references to battery OEMs for chemistry‑specific limits.