Brushless Motors on Embedded Systems Development

BLDC Fundamentals

Mon, 01 Jan 0001 00:00:00 +0000

BLDC Fundamentals#

A brushless DC motor (BLDC) replaces the mechanical commutator of a brushed motor with electronic switching. The rotor carries permanent magnets, and the stator has three sets of windings arranged 120° apart. By energizing the windings in the correct sequence at the correct rotor angle, the stator field continuously pulls the rotor forward. The result is higher efficiency (85–95 % vs 70–85 % for brushed), longer life (no brush wear), and better power density — at the cost of requiring a controller that knows the rotor position and drives a three-phase inverter.

Six-Step Commutation

Mon, 01 Jan 0001 00:00:00 +0000

Six-Step Commutation#

Six-step (trapezoidal) commutation is the simplest method for driving a BLDC motor. At any instant, two of the three phases are energized (one high, one low) while the third floats. As the rotor advances through 60° electrical increments, the firmware switches to the next commutation state. The sequence repeats every 360° electrical — six states per electrical revolution, hence the name. This approach requires only six discrete switching states and can be driven from three Hall-effect sensors or sensorless back-EMF detection.

Field-Oriented Control

Mon, 01 Jan 0001 00:00:00 +0000

Field-Oriented Control#

Field-oriented control (FOC), also called vector control, is the gold standard for BLDC and PMSM motor control. Instead of switching between six discrete commutation states, FOC treats the motor as a DC machine by transforming the three-phase stator currents into a two-component rotating reference frame aligned with the rotor. This allows independent control of torque-producing current (Iq) and field-weakening current (Id), producing smooth, ripple-free torque at all speeds. The trade-off is significantly more math per control cycle — Clarke and Park transforms, two PID loops, inverse transforms, and space-vector PWM — all running at 10–40 kHz.

ESC Integration

Mon, 01 Jan 0001 00:00:00 +0000

ESC Integration#

An electronic speed controller (ESC) is a self-contained BLDC driver that handles commutation, current regulation, and protection — reducing the firmware interface to a single control signal. ESCs originated in the RC hobby world but are now used in drones, robots, electric vehicles, and any application where the complexity of building a custom three-phase inverter is not justified. The MCU sends a throttle command; the ESC manages everything else.

Sensorless Back-EMF

Mon, 01 Jan 0001 00:00:00 +0000

Sensorless Back-EMF#

Eliminating Hall sensors from a BLDC motor reduces cost, connector count, and failure points — but the controller must determine rotor position from the motor’s own electrical signals. The dominant technique for trapezoidal (six-step) sensorless drives is back-EMF zero-crossing detection: when one phase is floating (undriven), its terminal voltage crosses the virtual neutral point at a predictable rotor angle. Detecting this crossing provides the timing reference for the next commutation event.