Sensorless BLDC Motor Controller

Sensorless BLDC drives reduce cost and wiring complexity by eliminating Hall sensors, but they require careful analog front-end design and timing-critical firmware to reconstruct rotor position from back-EMF.

This project builds a self-contained controller that can start, accelerate, and regulate a BLDC motor using six-step commutation derived from floating-phase zero-crossing events.

• Reliable six-step sensorless commutation
• Gate-drive stage with intentional dead time
• Over-current and over-temperature protection
• ~20 kHz PWM suitable for small BLDC motors
• Bring-up path that is measurable on a lab bench (scope, current probe)

The system is organized as:

1. Power stage — six-MOSFET three-phase inverter
2. Gate drivers — isolated/level-shifted drive with dead-time enforcement
3. Sense chain — floating-phase back-EMF dividers, shunt current sense, temperature sensor
4. Controller — Teensy 4.1 running PWM timers, ADC sampling, and commutation state machine

Commutation advances on predicted or measured zero-crossings with a 30° electrical delay typical of six-step sensorless schemes.

The custom KiCad PCB integrates the inverter, gate drivers, sensing networks, and Teensy interface.

Key hardware choices: - Discrete MOSFET half-bridges sized for prototype current - Resistive dividers for floating-phase back-EMF measurement - Shunt-based current sensing into the ADC - Temperature monitoring for thermal shutdown

*[Placeholder: replace with annotated PCB screenshots and schematic excerpts.]*

Firmware is structured as a real-time control loop:

• PWM generation with complementary outputs and dead time
• ADC sampling synchronized to PWM edges where possible
• Zero-crossing detection and commutation advance
• Fault handling for over-current / over-temperature

Open-loop start-up ramps into closed-loop sensorless tracking once back-EMF amplitude is usable.

• Six-step over FOC for a clearer bring-up path and educational transparency of back-EMF sensing
• Teensy 4.1 for fast timers, plenty of PWM channels, and easy bench iteration
• Discrete inverter to keep the power path inspectable and easy to probe

Planned / in-progress validation: - Gate waveforms and dead-time verification on a scope - Back-EMF waveform capture on a spinning motor - Current-limit trip testing with a current-limited supply - Thermal soak under load

*[Placeholder: add scope captures and test logs as they become available.]*

Project is currently in development. Early bring-up focuses on reliable open-loop spin-up and clean zero-crossing detection before closed-loop speed control.

• Distinguishing true zero-crossings from PWM switching noise
• Stable start-up before back-EMF is large enough to sense
• Layout parasitics around the inverter switching nodes

Sensorless control is as much an analog layout problem as a firmware problem. Probe access, ground referencing, and filtering dominate early bring-up time.

• Closed-loop speed regulation
• Soft-start and stall detection refinements
• Optional FOC migration path
• Full 3D PCB model for the interactive viewer