Offset angle determination for synchronous machines

1. A method for determining offset angles of an electric machine including a stator, a rotor, and a shaft connected to the rotor, the method comprising:

providing the shaft in a generally no-load state;

positioning the rotor with respect to the stator at a first field angle which corresponds to an orientation of a rotor magnetic field generated by the rotor relative to an orientation of a stator magnetic field generated by the stator;

applying a current to the stator windings to generate a rotating stator magnetic field and set the rotor to a first rotational speed;

detecting a first sensor angle by measuring using an angle sensor which is connected to the shaft;

determining a first offset angle as a function of a difference between the first field angle and the first sensor angle;

accelerating the rotor to a second rotational speed that is higher than the first rotational speed by providing the stator magnetic field;

de-energizing all stator windings of the stator while the rotation is continued by inertia;

detecting a second field angle by measuring a variation over time of an induced voltage which is induced within the electric machine by the rotation of the rotor;

detecting an instant at which induction voltages of two stator windings are equal;

measuring a second sensor angle at the instant at which the induction voltages of two stator windings are equal; and

determining a second offset angle as a function of a difference between the second field angle and the second sensor angle,

wherein the stator magnetic field is a stationary or rotating field; and

wherein setting the rotor in rotation to the first rotational speed occurs prior to detecting the second field angle such that the rotor remains in a rotating state after the stator magnetic field is de-energized when measuring the induced voltage.

2. The method as recited in claim 1 , wherein the rotor is positioned by impressing a slowly rotating stator magnetic field having a rotational speed for which air resistance, bearing friction, and other loads which inhibit rotation of the rotor are negligible, and the first field angle is an angle which: i) corresponds to an orientation of the stator winding which generates the stator magnetic field, or ii) corresponds to a mean of angles of all stator windings weighted according to an exerted force on the rotor.

3. The method as recited in claim 1 , wherein one of: i) the first offset angle is the difference between the first field angle and the first sensor angle, or ii) the first offset angle is provided as a sum of a correction angle and the difference between the first field angle and first sensor angle, the correction angle corresponding to an error angle position between a zero position angle in which no force is exerted on the rotor, and an angle in which a force is exerted on the rotor which is equal to frictional force acting on the rotor.

4. The method as recited in claim 1 , wherein the second field angle is detected by phase detection of the induced voltage which is induced in the stator, the rotation of the rotor in each case induces voltage in at least two stator windings which are oriented at different alignment angles, and the second sensor angle is provided by the geometric center of the alignment angles when the induced voltages of different stator windings are equal.

5. The method as recited in claim 1 , wherein detecting the second field angle includes comparing an instantaneous amplitude of induced voltages which are generated in at least two different stator windings by rotation of the rotor, the stator windings being oriented at different alignment angles.

6. The method as recited in claim 1 , wherein the rotor is positioned by impressing a rotating stator magnetic field, and the field angle and the sensor angle are detected at the same time.

7. The method as recited in claim 1 , wherein the electric machine is at least one of a synchronous machine, an externally excited or self-excited synchronous machine, a permanently excited synchronous machine, a synchronous machine which is provided as an electrical traction module of a hybrid drive, or a direct current machine.

8. A method for determining offset angles of an electric machine including a stator, a rotor, and a shaft connected to the rotor, the method comprising:

providing the shaft in a generally no-load state;

positioning the rotor with respect to the stator at a first field angle which corresponds to an orientation of a rotor magnetic field generated by the rotor relative to an orientation of a stator magnetic field generated by the stator;

detecting a first sensor angle by measuring using an angle sensor which is connected to the shaft, the detected first sensor angle being associated with the first field angle;

detecting a first offset angle as a function of a difference between the first field angle and the first sensor angle;

after the first offset angle has been detected, setting the rotor in rotation by providing the stator magnetic field; and

after the rotor has been set in rotation, detecting a second offset angle as a function of a difference between a second field angle and a second sensor angle, all of the stator windings of the stator being de-energized while the rotation is continued, the second sensor angle being measuring by using the angle sensor which is connected to the shaft, the second field angle being detected by measuring variation over time of the induced voltage which is induced within the electric machine by the rotation of the rotor, and the second sensor angle being associated with the second field angle,

wherein the stator magnetic field is one of a stationary rotating field; and

wherein setting the rotor in rotation occurs prior to detecting the second field angle such that the rotor remains in a rotating state after the stator magnetic field is de-energized when measuring the induced voltage.

9. An angle detection device comprising:

an input connection to detect an angle signal which represents sensor angles;

an input connection to detect an induced voltage signal which indicates an induced voltage which is generated by rotation of a rotor in an electric machine;

an output connection to output a control signal for the electric machine; and

a data processing unit to:

position the rotor with respect to stator in the electrical machine at a first field angle which corresponds to an orientation of a rotor magnetic field generated by the rotor relative to an orientation of a stator magnetic field generated by the stator,

detect a first sensor angle by measuring using an angle sensor which is connected to a shaft connected to the rotor, the detected first sensor angle being associated with the first field angle,

calculate a first offset angle as a function of a difference between the first field angle and the first sensor angle,

set the rotor in rotation by providing the stator magnetic field,

de-energize all stator windings of the stator while the rotation is continued,

detect a second field angle by measuring the variation over time of an induced voltage which is induced within the electric machine by the rotation of the rotor,

detect a second sensor angle by measuring using an angle sensor which is connected to a shaft connected to the rotor, the second angle being associated with the second field angle, and

calculate a second offset angle as a function of a difference between the second field angle and the second sensor angle,

wherein the stator magnetic field is one of a stationary or rotating field, the rotor being positioned by using the control signal; and

wherein setting the rotor in rotation occurs prior to detecting the second field angle such that the rotor remains in a rotating state after the stator magnetic field is de-energized when measuring the induced voltage.

10. An angle detection device comprising:

an input connection to detect an angle signal which represents a sensor angle;

an input connection to detect an induced voltage signal which indicates an induced voltage which is generated by rotation of a rotor in an electric machine;

an output connection to output a control signal for the electric machine; and

a data processing unit to:

position the rotor with respect to stator in the electrical machine at a field angle which corresponds to an orientation of a rotor magnetic field generated by the rotor relative to an orientation of a stator magnetic field generated by the stator,

detect the sensor angle by measuring using an angle sensor which is connected to a shaft connected to the rotor, the detected sensor angle being associated with the field angle,

detect a first field angle corresponding to an angular winding of the stator which exerts a force on the rotor,

calculate a first offset angle as a function of a difference between the field angle and the sensor angle,

after the first offset angle has been calculated, set the rotor in rotation by providing the stator magnetic field, and

after the rotor has been set in rotation, all of the stator windings of the stator being de-energized while the rotation is continued, detect a second field angle being detected by measuring variation over time of the induced voltage which is induced within the electric machine by the rotation of the rotor, and

calculate at least one second offset angle as a function of a difference between the second field angle and the sensor angle,

wherein the rotor is positioned by using the control signal; and

wherein setting the rotor in rotation occurs prior to detecting the second field angle such that the rotor remains in a rotating state after the stator magnetic field is de-energized when measuring the induced voltage.