Unattenuated BEMF detection for sensorless brushless DC (BLDC) motor drives

This paper develops an unattenuated BEMF detection method for sensorless BLDC motor drive. The unattenuated BEMF can be directly obtained from the terminal voltage of the floating phase without voltage-dividing and filtering. As a result, this approach makes it possible to detect the rotor position over a wide speed range, especially at a lower speed. A simply correction is proposed to asymmetry BEMF ZCP detection due to parasitic capacitance and discontinuous current at light load. The detailed schemes are analyzed and verified by experimental results.