Method for determining rotor position

Details Method for determining rotor position Method for determining rotor position

1999-10-01

2001-03-27

Nappi, Robert E. (Department: 2837)

Electricity: motive power systems

Synchronous motor systems

Armature winding circuits

C318S254100, C318S606000, 36

Reexamination Certificate

active

06208110

ABSTRACT:

BACKGROUND
The present invention relates generally to permanent magnet motors, and more particularly, to an improved magnet polarity detection technique for position sensorless permanent magnet motors, such as those that are used in electric vehicle and other applications.
The assignee of the present invention designs and develops electric vehicles and permanent magnet motors that are used to propel such vehicles. By using a technique disclosed in U.S. Pat. No. 5,585,709 issued to Jansen, for example, one can detect the position of a rotor of the permanent magnet motor but not the magnetic polarity. That is, the absolute position of the rotor is either the detected angle or the detected angle plus 180 degrees. This is due to the fact that the change in motor inductance is periodic over 180 electrical degrees, not 360 as would be required for unique detection. The present invention provides a solution to this problem.
It would therefore be desirable to have an improved magnet polarity detection technique for position sensorless permanent magnet motors.
SUMMARY OF THE INVENTION
The present invention comprises a method for use in determining the absolute position of a rotor of a permanent magnet motor. A preferred embodiment of the method comprises the following steps. The angular position of the direct axis of the rotor is detected. The polarity of the rotor is then detected to determine the absolute position of the rotor.
In a preferred example, this invention determines the polarity of the rotor and therefore the absolute position according to the steps of: applying a square wave voltage to the motor stator to generate an mmf vector parallel to the direct axis of the rotor; measuring the phase currents of the motor stator; calculating the direct axis current responsive to the measured phase currents and the angular position; time averaging the direct axis current; determining that the rotor is aligned with the mmf vector if the time average is offset positive; and determining that the rotor is 180 degrees out of phase with the mmf vector if the time average is offset negative.


REFERENCES:
patent: 4814677 (1989-03-01), Plunkett
patent: 5144564 (1992-09-01), Naidu et al.
patent: 5585709 (1996-12-01), Jansen et al.

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