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We have analyzed the characteristics of terminal voltages used to detect rotor position in interior permanent-magnet (IPM) brushless DC (BLDC) motors in sensorless control by employing a two-phase conduction method. We found that a detected zero crossing point (ZCP) of the open phase voltage advances the real rotor position due to additional voltage components caused by variation of inductance with rotor position. We conclude that the amount of position error is related to rotor saliency, load, and motor speed. We also present the relationship between abnormal currents and amount of position errors in the sensorless controller by using simulations that take into account additional voltages in our model of terminal voltages and motor neutral voltage as well as experiments with a position sensor. We verified the validity of our analysis on IPM motors having various motor parameters under sensorless control.
Date of Publication: Aug. 2008