Measuring the Phase Shift Between Hall Signals and Phase Voltages for Purpose of End Quality Control of BLDC Motor Production

Abstract

BLDC motors for demanding applications require a sensor system for electronic commutation to determine the current rotor position. Often, three Hall magnetic sensors, angularly displaced by 60º or 120º, are used for this purpose. Ideally, commutation should be performed precisely at the rotor position where the back induced electromotive force (BEMF) crosses the zero value. However, in reality, the deviation (phase shift between the voltage crossing the zero value and the HALL sensor switching) is different from 0º and depends on the mechanical tolerances of motor manufacturing, sensor soldering position, and rotor magnetization repeatability. To perform comprehensive final testing of motors, a dedicated measuring method had to be developed, as professional measuring instruments (Frequency counters) are not suitable for this purpose. This is due to winding voltage not being sinusoidal but pulse-width modulated. It is also not possible to rotate the motor during testing with an additional drive. Consequently, that is why the measurement can only be performed during the coast-down period, when the rotational speed exponentially decreases. In this paper, we present a solution, developed for the EOL (end-of-line) quality assessment production of electric motors (BLDCs) at Domel company. It consists of a PCB for signal preparation, a fast USB module for simultaneous acquisition of analog signals, software for data processing, result analysis and result presentation and company database for results storage.