Motor commutation
Before delving into the BLDC motor feedback options, it's important to understand why you need them. BLDC motors can be configured for single phase, two phase and three phase; the most common configuration is three phase. The number of phases matches the number of stator windings, and the number of rotor poles can be any number depending on the application requirements. Because the rotor of a BLDC motor is affected by the rotating stator poles, the stator pole position must be tracked to effectively drive the three motor phases. To do this, a six-step commutation mode is generated on the three motor phases using a motor controller. These six steps (or commutation phases) move the electromagnetic field, which in turn causes the rotor permanent magnet to move the motor shaft.
By using this standard motor commutation sequence, the motor controller can use high frequency pulse width modulation (PWM) signals to effectively reduce the average voltage experienced by the motor and thus the motor speed. In addition, this setup greatly enhances design flexibility by allowing a single voltage source to be used in a wide variety of motors, even when the DC voltage source is significantly higher than the rated voltage of the motor. In order to maintain this system's efficiency advantage over brushed technology, a very tight control loop needs to be installed between the motor and the controller. The importance of feedback technology is here; the controller must be able to maintain precise control of the motor, and it must always know the exact position of the stator relative to the rotor. Any misalignment or phase shift between the expected and actual locations may result in unexpected conditions and performance degradation. There are many ways to achieve this feedback for BLDC motor commutation, but the most common way is to use a Hall effect sensor, encoder or resolver. In addition, some applications rely on sensorless commutation technology to achieve feedback.
