Patent ID: 8350505

Claim:
A method for ascertaining a correction value for an angular position of a rotor of an electrically commutated reversible synchronous motor based on an external sensor used to detect a position of the rotor and control driving the synchronous motor in a normal operating mode, the method comprising: driving the synchronous motor in a forward calibration journey, by an externally forced rotating field, which is formed independently of the external sensor that detects the position of the rotor; during the forward calibration journey, simultaneously measuring an electrical angle of the rotating field and a mechanical angle of the rotor, the mechanical angle of the rotor being measured by the external sensor, the electrical angle and the mechanical angle being measured for at least one reference position in the forward calibration journey; determining a first angular difference between the electrical angle of the rotating field and the mechanical angle of the rotor, as measured during the forward journey; reversing a direction of the externally forced rotating field to thereby drive the synchronous motor in a reverse calibration journey; during the reverse calibration journey, simultaneously measuring the electrical angle of the rotating field and the mechanical angle of the rotor, the mechanical angle of the rotor being measured by the external sensor; determining a second angular difference between the electrical angle of the rotating field and the mechanical angle of the rotor, as measured in the reverse calibration journey; and determining the correction value for an actual phase displacement angle by averaging the first and second angular differences.