An electronic Brushless DC Controller (also known as a Driver, or Electronic Speed Controller), replaces the mechanical commutation system utilized by a Brush DC Motor, and is required by most Brushless DC Motors to operate. In a Brushless DC Motor controller, either a Hall Effect Sensor or Back EMF (Electromotive Force) is used to identify the position of the rotor. Understanding the orientation of the rotor is crucial to operating the Brushless DC Motor.
The Hall Effect uses three hall sensors within the Brushless DC Motor to help detect the position of the rotor. This method is primarily used in speed detection, positioning, current sensing, and proximity switching. The magnetic field changes in response to the transducer that varies its output voltage. Feedback is created by directly returning a voltage, because the sensor operates as an analogue transducer. The distance between the Hall plate and a known magnetic field can be determined with a group of sensors, and the relative position of the magnet can be deduced. A Hall sensor can act as an on/off switch in a digital mode when combined with circuitry.
Back EMF, also known as the Counter-Electromotive Force, is caused by a changing electromagnetic field. In a Brushless DC Motor, back EMF is a voltage that occurs where there is motion between the external magnetic field and the armature of the motor. In other words, the voltage is developed in an inductor by an alternating or pulsating current. The polarity of the voltage is constantly the reverse of the input voltage. This method is commonly used to measure the position and speed of the Brushless DC Motor indirectly, and due to the lack of Hall Sensors within the controller, these are often referred to as sensorless controllers.
Optical Encoders can also be added to the Brushless DC Motor, allowing both direction and speed to be determined. More precise applications may use Optical Encoders with a third index signal, to determine pulse per revolution.
- See more at: http://www.anaheimautomation.com/manuals/forms/brushless-dc-motor-guide.php#sthash.wu3GqqF9.CbYTs9N2.dpuf