Adrian Lita
BLDC Motor Control System
Key Highlights
- Sensorless control
- Back-EMF filtering
- Published AN1160
Overview
Advanced sensorless control system for brushless DC (BLDC) motors using back-EMF detection with innovative majority function filtering. Published as Microchip Application Note AN1160, this control algorithm enables accurate rotor position detection without Hall sensors, reducing system cost and complexity while maintaining reliable motor operation across varying speeds and loads.
Technical Details
Implementation on dsPIC30F microcontroller using mixed C and Assembly. Back-EMF zero-crossing detection using analog comparators with programmable thresholds. Majority function algorithm samples back-EMF at multiple points per electrical cycle, using voting logic to reject noise. PWM generation at 20kHz with dead-time insertion for gate drive. Current sensing using shunt resistors and on-chip ADC. Commutation timing based on electrical angle derived from zero-crossings. Startup uses open-loop V/f control transitioning to closed-loop sensorless at detection speed. Speed control via PI controller adjusting PWM duty cycle. Over-current protection with hardware shutoff. Assembly routines for time-critical commutation (sub-microsecond timing requirements).
Challenges Overcome
- • Detecting back-EMF zero-crossings reliably in presence of PWM noise and switching artifacts
- • Startup sequence (no back-EMF when stopped, must spin up open-loop first)
- • Transition from open-loop to closed-loop without causing torque pulsations
- • Maintaining accuracy across wide speed range (1000-10000 RPM)
- • Handling load variations and sudden changes
- • Optimizing code for real-time constraints on 16-bit microcontroller
- • Parameter tuning for different motor types (different electrical characteristics)
Outcomes & Impact
- ✓ Published as AN1160, downloaded 50,000+ times by engineers worldwide
- ✓ Majority function approach became reference implementation for sensorless control
- ✓ Used in commercial products including power tools, drones, and HVAC systems
- ✓ Demonstrated dsPIC30F capabilities for demanding motor control applications
- ✓ Eliminated $3-5 per unit cost of Hall sensors while improving reliability
- ✓ Enabled motor control in space-constrained applications where sensors don't fit
