A Brushless DC (BLDC) motor is a permanent magnet synchronous motor that uses position detectors and inverter to control the armature current. The motor drive system requires a rotor position sensor to provide the proper commutation sequence. The position sensors such as resolvers, absolute position encoders and Hall sensors increase the cost and size of the motor. A proposed scheme for rotor position sensor-less speed control of BLDC motors with different possible modes of stator pole generations is explained in this paper. Proper stator voltage sequence has to be generated to match with the rotor magnetic polarity to eliminate the requirement of rotor position sensors. Since the detected position information on the sensor-less rotor has some uncertainty, the brushless DC motor cannot be driven with a maximum torque.
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