Improved sensorless Brushless DC motor drive

This paper develops an improved sensorless Brushless DC (BLDC) motor drive. It is based on the sensorless control in reference [1], which describes a technique for directly extracting phase back EMF information without the need to sense or re-construct the motor neutral. The reference method is not sensitive to switching noise and requires no filtering, achieving much better performance than traditional back EMF sensing scheme. A simply correction is proposed to reduce the commutation acoustic noise caused by asymmetry back EMF ZCP detection due to parasitic capacitance and discontinuous current at light load. On the other hand, slope compensation is presented for the fixed frequency peak-sensing current control to reduce the acoustic noise caused by sub-harmonic oscillation. The detailed schemes are analyzed and experimental results verify the analysis.