Calibration and monitoring of an angle measuring system for electrical machines

1. An electrical machine, comprising:

an angular position transducer for identifying a first rotation angle of a rotor;

an exciter winding of the rotor, through which winding an exciter current flows;

a stator winding for generating a magnetic field;

a voltage measuring instrument for sensing a pole wheel voltage at ends of the stator winding upon a rotation of the rotor;

an identification circuit for identifying a second rotation angle from the pole wheel voltage and for identifying an angle difference between the first rotation angle and the second rotation angle; and

a comparator for comparing the pole wheel voltage with a reference voltage in order to generate a comparison signal;

wherein the exciter current is selected in such a way that the pole wheel voltage does not exceed a vehicle electrical system voltage;

wherein the comparator outputs the comparison signal as soon as the pole wheel voltage falls below the reference voltage; and

wherein the identification circuit identifies the angle difference when the comparison signal is present.

2. The electrical machine as recited in claim 1 , further comprising a memory for storing the angle difference.

3. The electrical machine as recited in claim 1 , further comprising a current limiter for limiting a maximum exciter current in the exciter winding.

4. The electrical machine as recited in claim 3 , wherein the current limiter sets the pole wheel voltage by setting a maximum exciter current below a reference voltage.

5. The electrical machine as recited in claim 1 , wherein the identification circuit corrects the first rotation angle by an amount equal to the angle difference in order to obtain a corrected rotation angle.

6. The electrical machine as recited in claim 5 , wherein the identification circuit compares the corrected rotation angle with the second rotation angle.

7. The electrical machine as recited in claim 6 , wherein the identification circuit outputs a fault signal if the corrected rotation angle and the second rotation angle deviate from one another.

8. The electrical machine as recited in claim 5 , further comprising a control application apparatus for generating a rotating field synchronously with the corrected rotation angle.

9. The electrical machine as recited in claim 1 , wherein a number of magnetic pole pairs is greater than one.

10. A method for operating an electrical machine, comprising:

sensing a first rotation angle of a rotor of the electrical machine by way of an angular position transducer;

sensing a pole wheel voltage at ends of a stator winding upon a rotation of the rotor;

identifying a second rotation angle from the pole wheel voltage;

comparing, using a comparator, the pole wheel voltage with a reference voltage in order to generate a comparison signal, wherein the comparator outputs the comparison signal as soon as the pole wheel voltage falls below the reference voltage;

identifying an angle difference between the first rotation angle and the second rotation angle, an identification circuit identifying the angle difference when the comparison signal is present; and

selecting an exciter current that flows through an exciter winding of the rotor in such a way that the pole wheel voltage does not exceed a vehicle electrical system voltage.

11. The method as recited in claim 10 , further comprising ascertaining the angle difference at multiple positions along a rotor periphery.

12. The method as recited in claim 10 , further comprising correcting the first rotation angle by an amount equal to the angle difference in order to obtain a corrected rotation angle.

13. The method as recited in claim 12 , further comprising generating a rotating field synchronously with the corrected first rotation angle.