Balancing Hall-Effect Signals in Low-Precision Brushless DC Motors

Brushless dc motors with Hall sensors are widely used in various electromechanical applications. These machines have been often considered in the literature, under one common assumption - ideal placement of the sensors, which is often not true, especially for the low-precision motors. The misalignment of Hall sensors leads to unbalanced operation of the inverter and motor phases, which in turn results in increased low-frequency harmonics in torque ripple and possible acoustic noise. This paper describes a straightforward technique to mitigate the influence of unbalanced sensors on the performance of the brushless dc motor drive system. The proposed method uses moving-average filtering of the Hall sensor signals to achieve performance characteristics very close to those of a motor with perfectly balanced Hall sensors. A verification study is performed to validate the analysis.