Energizing and measuring the temperature of stator windings in an at least motor-driven electric polyphase machine

1. A method for determining an ohmic resistance of stator windings of a rotating field machine operable in motor mode, in which for energizing the stator windings at least four degrees of freedom exist, the method comprising:

ascertaining the ohmic resistance of the stator windings by applying phase currents to the stator windings, the phase currents being predefined using a vector-based method;

wherein at least during the ascertainment of the ohmic resistance, the phase currents are predefined by the vector-based method in such a way that the phase currents oscillate with a phase-current amplitude and a phase-current frequency around average values, the phase-current amplitude and the phase-current frequency being determined based on at least one of a requested rotational speed and a requested torque, of the rotating field machine, the phase-current amplitude and the phase-current frequency being determined by the vector-based method using a first current vector, and the average values corresponding to bias currents, by which the phase currents are at least in part increased or reduced, and which are determined by the vector-based method, and which are determined in such a way that the phase currents exhibit no torque effectiveness in the rotating field machine, the bias currents being determined by the vector-based method using a second current vector different than the first current vector.

2. The method as recited in claim 1 , wherein the bias currents are predefined based on a transformation specification with which second current vectors, which are independent of torque-effective first current vectors, are converted into current values.

3. The method as recited in claim 1 , wherein the method is used to energize a rotating field machine, the rotating field machine being one of a synchronous or asynchronous machine.

4. The method as recited in claim 1 , wherein before the ohmic resistance of the stator windings is ascertained, the stator windings are energized for a predefined time by applying the predefined phase currents to the stator windings so that the stator windings heat up.

5. The method as recited in claim 1 , further comprising determining a temperature of the stator windings based on the determined ohmic resistance.

6. The method as recited in claim 1 , wherein:

the phase-current amplitude and the phase-current frequency are determined based on the transformation specification with which torque-effective first current vectors are converted into current values; and

the bias currents are determined based on the transformation specification with which second current vectors, which are independent of the torque-effective first current vectors, are converted into current values.

7. A control device of a rotating field machine operable in motor mode, the control device configured to:

ascertain an ohmic resistance of the stator windings by applying phase currents to the stator windings, the phase currents being predefined using a vector-based method, wherein at least during the ascertainment of the ohmic resistance, the phase currents are predefined by the vector-based method in such a way that the phase currents oscillate with a phase-current amplitude and a phase-current frequency around average values, the phase-current amplitude and the phase-current frequency being determined based on at least one of a requested rotational speed and a requested torque, of the rotating field machine, the phase-current amplitude and the phase-current frequency being determined by the vector-based method using a first current vector, and the average values corresponding to bias currents, by which the phase currents are at least in part increased or reduced, and which are determined by the vector-based method, and which are determined in such a way that the phase currents exhibit no torque effectiveness in the rotating field machine, the bias currents being determined by the vector-based method using a second current vector different than the first current vector.

8. A non-transitory machine-readable storage medium having a computer program for determining a temperature of stator windings of a rotating field machine operable in motor mode, in which for energizing the stator windings at least four degrees of freedom exist, the computer program, when executed by a processor, causing the processor to perform:

ascertaining an ohmic resistance of the stator windings by applying phase currents to the stator windings, the phase currents being predefined using a vector-based method;

wherein at least during the ascertainment of the ohmic resistance, the phase currents are predefined by the vector-based method in such a way that the phase currents oscillate with a phase-current amplitude and a phase-current frequency around average values, the phase-current amplitude and the phase-current frequency being determined based on at least one of a requested rotational speed and a requested torque, of the rotating field machine, the phase-current amplitude and the phase-current frequency being determined by the vector-based method using a first current vector, and the average values corresponding to bias currents, by which the phase currents are at least in part increased or reduced, and which are determined by the vector-based method, and which are determined in such a way that the phase currents exhibit no torque effectiveness in the rotating field machine, the bias currents being determined by the vector-based method using a second current vector different than the first current vector.