Get AN1083, Sensorless BLDC Control With Back-EMF Filtering. Application Note

Sensored control implies that you are using physical sensors on the motor to determine the exact position of the rotor. Sensorless control means that you are using other methods to estimate the rotor position without any physical sensors.

There is one major disadvantage to sensorless BLDC motor control; when the motor is stationary, no back EMF is generated, depriving the MCU of information about the stator and rotor position. The solution is to start the motor in an open loop configuration by energizing the coils in a pre-determined sequence.

Sensorless BLDC motor control—sometimes called sensorless trapezoidal control of BLDC motors—uses back EMF (BEMF) for determining the location of the motor's rotor (the motor's rotating part) with respect to the motor's stator (the stationary part).

There is one major disadvantage to sensorless BLDC motor control; when the motor is stationary, no back EMF is generated, depriving the MCU of information about the stator and rotor position. The solution is to start the motor in an open loop configuration by energizing the coils in a pre-determined sequence.

The control of BLDC motors can be done in sensor or sensorless mode, but to reduce overall cost of actuating devices, sensorless control techniques are normally used. The advantage of sensorless BLDC motor control is that the sensing part can be omitted, and thus overall costs can be considerably reduced.

The control of BLDC motors can be done in sensor or sensorless mode, but to reduce overall cost of actuating devices, sensorless control techniques are normally used. The advantage of sensorless BLDC motor control is that the sensing part can be omitted, and thus overall costs can be considerably reduced.

The sensorless BLDC motor controller works without a sensor; it detects the rotor's position by estimating back electromotive force (back EMF). This is the voltage created in the stator's windings by the rotating armature.

In place of using Hall-effect sensors for determining the rotor's position and/or speed, a phenomenon called back EMF is employed in a sensorless design. At high speed the ESC will alter the timing for the sequence of power pulses that are sent to the motor's windings, in turn improving efficiency and performance.