Sensorless BLDC Control with Back-EMF Filtering

This application note describes a sensorless brushless DC (BLDC) motor control algorithm, implemented using the dsPIC® digital signal controller (DSC). The algorithm works by digitally filtering the back-Electromotive Force (back-EMF) on each phase of the motor and determining when to commutate the motor windings based on the filtered back-EMF signals. This control technique precludes the need for discrete, low-pass filtering hardware and off-chip comparators.

BLDC motors are used in a variety of applications. The algorithm described in this application note targets BLDC motors that operate in the 40k to 100k electrical RPM range. Some BLDC motor applications that run in this RPM range are model RC motors, fans, hard drives, air pumps and dental drills.