Method and device for determining phase currents and an excitation current of an electrical machine, and motor system

1. A method for determining phase currents through phase windings ( 12 ) and a field current through a field winding ( 13 ) of an electrical machine ( 11 ), wherein the field winding ( 13 ) is connected between a star point ( 14 ) of the phase windings ( 12 ) and a specific reference potential ( 17 ), and a current measuring apparatus is connected between the connection of the field winding ( 13 ) to the specific reference potential ( 17 ) and the phase windings ( 12 ), the method comprising:

periodically driving the electrical machine ( 11 ) with a predefined pulse pattern ( 30 );

determining in each case one measurement current (I measure ) by the current measuring apparatus in a plurality of time measurement windows ( 31 , 32 , 33 ) of a measurement period ( 37 ), wherein the measurement currents (I measure ) comprise a current through one of the phase windings ( 12 ) and at least one current through one or more parallel circuits of a plurality of the phase windings ( 12 ); and

determining the phase currents and the field current by the current measuring apparatus by evaluating the measurement currents (I measure ) which are determined during the measurement period ( 37 );

wherein the electrical machine ( 11 ) is driven by pulse width modulation signals, wherein, during each measurement window ( 31 , 32 , 33 ), the number of phase windings ( 12 ), which are each connected to the specific reference potential ( 17 ), is different and the remaining phase windings ( 12 ) are each connected to a potential which is different from the specific reference potential; and

a measurement current (I measure ) which corresponds to the field current is determined by the current measuring apparatus, depending on whether all phase windings ( 12 ) are connected to the specific reference potential ( 17 ) for a prespecified minimum period of time in an actual measurement period ( 37 ).

2. The method as claimed in claim 1 , wherein an assessment as to whether the measurement current (I measure ) which corresponds to the field current is measured in the actual measurement period ( 37 ) and is performed on the basis of the instantaneous load on the electrical machine ( 11 ).

3. The method as claimed in claim 1 , wherein the electrical machine ( 11 ) has three phase windings ( 12 ), wherein, during each measurement period ( 37 ), a first phase current is measured as a measurement current (I measure ) in a first measurement window ( 31 ), and a linear combination of a second phase current with the field current is measured as a measurement current (I measure ) in a second measurement window ( 32 ), and wherein a current value of the field current, which current value is measured in a third measurement window ( 33 ), or the a stored and/or calculated current value of the field current is used.

4. The method as claimed in claim 3 , wherein the current value of the field current, or the stored and/or calculated current value of the field current is used to determine a third phase current.

5. The method as claimed in claim 1 , wherein the pulse width modulation signals are left-aligned.

6. The method as claimed in claim 1 , wherein the remaining phase windings ( 12 ) are each connected to a supply voltage connection ( 16 ).

7. The method as claimed in claim 1 , wherein a stored and/or calculated current value is assumed for the field current, depending on whether all phase windings ( 12 ) are connected to the specific reference potential ( 17 ) for a prespecified minimum period of time in the actual measurement period ( 37 ).

8. The method as claimed in claim 1 , wherein the prespecified minimum period of time in the actual measurement period ( 37 ) is in a time range at the end of a pulse width modulation period ( 38 ).

9. An apparatus for determining phase currents through phase windings ( 12 ) and a field current through a field winding ( 13 ) of an electrical machine ( 11 ), in which the field winding ( 13 ) is connected between a star point ( 14 ) of the phase windings ( 12 ) and a specific reference potential, the apparatus comprising:

a current measuring apparatus is connected between the connection of the field winding ( 13 ) to the specific reference potential ( 17 ) and the phase windings ( 12 ), wherein the apparatus is configured to perform the steps of:

determining in each case one measurement current (I measure ) in a plurality of time measurement windows ( 31 , 32 , 33 ) of a measurement period ( 37 ) in the electrical machine ( 11 ) which is periodically driven with a predefined pulse pattern ( 30 ), wherein the measurement currents (I measure ) correspond to currents through one of the phase windings ( 12 ) and through one or more parallel circuits of a plurality of the phase windings ( 12 ); and

determining the phase currents and the field current by evaluating the measurement currents (I measure ) which are determined during the measurement period ( 37 )

driving the electrical machine ( 11 ) by pulse width modulation signals, wherein, during each measurement window ( 31 , 32 , 33 ), the number of phase windings ( 12 ), which are each connected to the specific reference potential ( 17 ), is different and the remaining phase windings ( 12 ) are each connected to a potential which is different from the specific reference potential; and

determining a measurement current (I measure ) which corresponds to the field current, depending on whether all phase windings ( 12 ) are connected to the specific reference potential ( 17 ) for a prespecified minimum period of time in an actual measurement period ( 37 ).

10. A motor system ( 10 ), comprising:

an electrical machine ( 11 ) with external or hybrid excitation, which electrical machine has a field winding ( 13 ) which is connected between a star point ( 14 ) of the phase windings ( 12 ) and a specific reference potential;

a driver circuit ( 15 ) by which electrical energy is supplied to the phase windings ( 12 ) and which supplies current to the phase windings ( 12 ) in accordance with a pulse pattern ( 30 );

a current measurement device ( 24 ) which is arranged between the driver circuit ( 15 ) and the specific reference potential, so that an associated measurement current (I measure ) is determined in a measurement window ( 31 , 32 , 33 ), said measurement current flowing through one of the phase windings ( 12 ) or a parallel circuit of a plurality of the phase windings ( 12 ) altogether in a corresponding manner with respect to a predetermined current direction; and the apparatus as claimed in claim 9 .

11. The motor system ( 10 ) as claimed in claim 10 , wherein the driver circuit ( 15 ) comprises an inverter with a bridge circuit.

12. The motor system ( 10 ) as claimed in claim 10 , wherein a drive unit ( 26 ) is provided in order to generate a plurality of time measurement windows ( 31 , 32 , 33 ) in the measurement period ( 37 ) of the measurement operation by driving the driver circuit ( 15 ) by in each case one or more phase windings ( 12 ) being simultaneously coupled to the connection ( 28 ) of the specific reference potential in accordance with a predefined pulse pattern ( 30 ).

13. The motor system ( 10 ) as claimed in claim 11 , wherein the bridge circuit, is a B6 bridge circuit.