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Analysis and improvement of low precision Hall-sensor-controlled brushless dc motors

University of British Columbia

Hall-sensor-based Brushless dc (BLDC) motors are becoming very popular in wide range of applications, mainly due to their low cost, high efficiency, and reliable operation as compared to the conventional brushed motors. These machines have been extensively researched in the literature mainly under two common assumptions: each Hall-sensor produce square-wave signal of exactly 180 electrical degrees; and that the signals from the three Hall-sensors are exactly 120 electrical degrees apart. These assumptions are not necessarily the case, particularly for low to medium cost motors. A recently published manuscript investigated operation of motors with unbalanced Hall-sensor signals and introduced inaccurate positioning of the sensors as the cause of the unbalance. There, solutions have been proposed to mitigate the adverse effects of sensor positioning errors on performance of the motor. This thesis builds upon this recent publication by identifying another source of error in the Hall-sensor signals. Here, it is shown that inaccurate positioning of the Hall sensors and uneven magnetization of the tablet with which the Hall sensors react are the major factors contributing to the distortion of Hall sensor signals. It is shown here that errors in the Hall sensor signals result in unsymmetrical operation of the inverter which in turn leads to low-frequency harmonics in the electromagnetic torque; increases torque ripple and acoustic noise; and degrade overall dynamic performance of the drive. A control-level approach is proposed to mitigate the adverse effects of the errors in the Hall-sensor signals. In this approach a multi-stage digital filtering block is added to remove the errors in the original Hall-sensor signals. Each stage of the filter is designed to cancel the undesirable harmonics due to one of the error sources, the unevenly magnetized reaction tablet and the misaligned Hall sensors. An efficient realization of the proposed filter is presented that makes it possible to be potentially programmed inside existing motor controllers or implemented in a stand-alone microcontroller which can be packaged into a dongle circuit. The operation of typical low-precision industrial BLDC motors with the proposed filtering approach is shown to approach the performance of the motors with ideal Hall sensors.

Text

2011-03-31

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/24224

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/