Atmel AVR443: Sensor-based Control of Three Phase Brushless DC Motor

In a Universal DC motor, brushes control the commutation by physically connecting the coils at the correct moment. In BLDC motors the commutation is controlled by electronics. The electronics can either have position sensor inputs that provide information about when to commutate or use the Back Electromotive Force generated in the coils. Position sensors are most often used in applications where the starting torque varies greatly or where a high initial torque is required. Position sensors are also often used in applications where the motor is used for positioning. Sensor-less BLDC control is often used when the initial torque does not vary much and where position control is not in focus, e.g. in fans.