Improving Dynamic Performance of Low-Precision Brushless DC Motors with Unbalanced Hall Sensors

Brushless DC motors controlled by Hall-effect sensors are widely used in various applications and have been extensively researched in the literature, mainly under the assumption that the Hall sensors are ideally placed 120 electrical degrees apart. However, this assumption is not always valid; in fact, sensor placement may be significantly inaccurate, especially in medium- and low-precision brushless DC machines. This paper shows that misplaced Hall sensors lead to unbalanced operation of the inverter and motor phases, which increases the low-frequency harmonics in torque ripple, causing increased vibrations, acoustic noise, and degradation of the overall drive performance. The paper also presents several average-filtering techniques that can be applied to the original Hall-sensor signals to mitigate the effect of unbalanced placement during steady state and transient operation. The proposed methodology is shown to achieve dynamic performance similar to that of a brushless Dc motor with accurately positioned Hall sensors.