Electric machine, activation unit and method for operating an electric machine

Abstract

An electric machine (21) having a stator (20) and having a rotor (29) rotatably mounted to the stator (20) is specified. The stator (20) comprises a stator winding (24), at least three teeth (23), and at least three grooves (22). In each case, one tooth (23) of the stator (20) is arranged between two grooves (22) along a circumference of the stator (20), and the stator winding (24) has at least three coils (25), wherein each of the coils (25) is wound around a tooth (23) of the stator (20), so that the stator winding (24) is a concentrated winding. In addition, the winding direction of all coils (25) is the same, each of the coils (25) is designed to be fed with its own phase current, and the stator (20) is designed to generate at least two rotary fields having different numbers of pole pairs independently of each other, in particular simultaneously. In addition, an activation unit (40) for the electric machine (21) and a method for operating an electric machine (21) are specified.

Claims

1. An electric machine having a stator and having a rotor rotatably mounted relative to the stator, wherein the stator comprises: a stator winding; at least three teeth; and at least three grooves, wherein: each tooth of the at least three teeth is arranged along a circumference of the stator between two grooves, the stator winding comprises at least three coils, wherein each of the at least three coils is wound around a tooth of the stator so that the stator winding is a concentrated winding, a winding direction of all of the at least three coils is the same, each of the at least three coils is configured to be fed with its own phase current, and the stator is configured to generate, using only one stator winding which is the stator winding, at least two rotary fields with different numbers of pole pairs independently of one another, in particular simultaneously.

2. The electric machine according to claim 1, in which the phase currents are out of phase with each other.

3. The electric machine according to claim 1, in which a coil of the stator winding is wound around each tooth of the stator.

4. The electric machine according to claim 1, in which the at least three coils are electrically connected to each other on a first side of the stator via a short-circuit means.

5. The electric machine according to claim 1, in which the at least three coils each comprise a single conductor or each comprise a plurality of conductor filaments that are connected electrically in parallel and arranged parallel to each other.

6. The electric machine according to claim 1, in which the stator is configured to generate at least one rotary field in which the number of pole pairs is variable.

7. The electric machine according to claim 1, in which the number of conductor sections of the at least three coils on two neighboring grooves are different.

8. The electric machine according to claim 1, wherein the rotor has an excitation winding and a field winding.

9. The electric machine according to claim 8, wherein the excitation winding has at least three coils, and each of the at least three coils of the excitation winding is connected to a respective separate rectifier.

10. An activation unit for the electric machine according to claim 1, having a compensation unit which is configured to generate compensation signals for at least partially compensating at least one undesired component of a magnetic force, wherein the magnetic force is induced by a rotary field generated by the stator during operation of the electric machine.

11. The activation unit according to claim 10, in which the compensation signals are generated at least one predeterminable operating point of the electric machine.

12. A method for operating an electric machine, the method comprising: providing a stator of the electric machine with at least three teeth, at least three grooves and a stator winding which has at least three coils; and feeding the at least three coils of the stator with separate phase currents, wherein: each tooth of the at least three teeth of the stator is arranged along a circumference of the stator between two grooves, each of the at least three coils is wound around a tooth of the stator so that the stator winding is a concentrated winding, a winding direction of all of the at least three coils is the same, and the stator is configured to generate, using only one stator winding which is the stator winding, at least two rotary fields having different numbers of pole pairs, in particular simultaneously.

13. The method for operating the electric machine according to claim 12, the method comprising: generating at least one rotary field by the stator during operation of the electric machine; generating at least three compensation signals by a compensation unit, wherein each compensation signal is associated with a respective phase current; and superimposing each of the at least three compensation signals over the respective associated phase current, wherein at least one undesired component of a magnetic force induced by the at least one rotary field is at least partially compensated.

Description

(1) In the following, the electric machine described here, the activation unit and the method for operating an electric machine are explained in more detail in connection with embodiments and the associated figures.

(2) FIG. 1 shows a schematic cross-section through an embodiment of a stator.

(3) FIG. 2 shows a schematic structure of an embodiment of a stator.

(4) The construction of a coil is shown by way of example in FIGS. 3A and 3B.

(5) FIGS. 4, 5, 6, 7A, 7B, 8A and 8B show arrangements of the stator winding according to various embodiments.

(6) FIGS. 9A, 9B, 9C and 10 show the magnetomotive force for various embodiments of a stator.

(7) FIGS. 11A and 11B show schematic cross-sections through further embodiments of a stator.

(8) FIG. 12 specifies the winding factors for various embodiments of a stator.

(9) Compensation components are shown by way of example in FIGS. 13A and 13B.

(10) FIG. 14 shows a schematic structure of an embodiment of an activation unit.

(11) FIG. 15 shows a cross-section through an embodiment of an electric machine.

(12) FIG. 16 shows the force density for an embodiment of an electric machine.

(13) FIG. 17 shows, by way of example, the compensation of a component of a magnetic force for an embodiment of an electric machine.

(14) FIGS. 18A and 18B show a stator for an electric machine.

(15) FIGS. 19A, 19B, 19C and 19D show an embodiment of a rotor.

(16) FIG. 1 shows a schematic cross-section through an embodiment of a stator 20 for an electric machine 21. The stator 20 extends along a longitudinal axis which runs perpendicular to the surface of the cross-section. The cross-section of the stator 20 is circular. The stator 20 has the shape of a hollow cylinder. A rotor 29 can be arranged in the interior of the stator 20.

(17) The stator 20 has a stator winding 24. The stator winding 24 has eleven coils 25. Each of the coils 25 is wound around a tooth 23 of the stator 20. The stator winding 24 is a concentrated winding. The winding direction of the eleven coils 25 is the same for all coils 25. The winding direction of each of the coils 25 is specified with plus and minus signs. The stator 20 further has eleven teeth 23, which are uniformly distributed along a circumference of the stator 20. The teeth 23 can be formed such that in each case a recess is arranged between two teeth 23. In addition, the stator 20 has 11 grooves 22. The grooves 22 are uniformly distributed along the circumference of the stator 20. One tooth 23 of the stator 20 is arranged in each case between two grooves 22 along the circumference of the stator 20.

(18) Each of the coils 25 forms an electrical phase of the stator winding 24. In addition, each of the coils 25 is designed to be fed with its own phase current. For this purpose, each of the coils 25 is connected to its own power supply unit 31. Since each of the coils 25 can be driven separately by its own power supply unit 31, the phase currents can be out of phase with each other. The stator 20 is designed to generate at least two rotary fields having different numbers of pole pairs independent of each other, in particular simultaneously.

(19) FIG. 2 shows a schematic structure of an embodiment of the stator 20. The stator 20 has a plurality of coils 25 which are each connected to a power supply unit 31 of its own.

(20) By way of example, five coils 25 with their power supply units 31 are shown in FIG. 2. The coils 25 are electrically connected to each other via a short-circuit means 28 on a first side 26 of the stator 20. The coils 25 are connected to their respective power supply units 31 on a second side 27 facing away from the first side 26.

(21) FIG. 3A shows the structure of a coil 25 by way of example. The coil 25 has, by way of example, three conductor sections 32. The conductor sections 32 extend mainly along the longitudinal axis of the stator 20. In addition, the winding direction of the coils 25 is specified schematically. Two of the conductor sections 32 extend in one direction, which is illustrated by two plus signs, and another conductor section 32 extends in the opposite direction, which is illustrated by a minus sign. In other words, the coil 25 has a total of 1.5 windings 44. The coil 25 is electrically connected to the short-circuit means 28 on the first side 26. The coil 25 is electrically connected to a power supply unit 31 on the second side 27. In this embodiment, the coil 25 comprises a single conductor.

(22) FIG. 3B shows a cross-section through a conductor section 32 of a coil 25 by way of example. The coil 25 comprises a plurality of conductor filaments arranged parallel to each other and electrically connected in parallel. Skin effects can thus be avoided or reduced.

(23) FIG. 4 shows the arrangement of the stator winding 24 according to an embodiment. For this purpose, a cross-section through the stator 20 is shown projected in a plane. The teeth 23 are shown arranged next to each other. The coils 25 are wound around the teeth 23 and arranged in the grooves 22. The open side of the grooves 22 can point, for example, in the direction of a rotor 29, which can be arranged in the stator 20. Each of the coils 25 has three conductor sections 32, which are marked by plus and minus signs. The longitudinal axis of the stator 20 thus extends perpendicular to the image plane. Two of the coils 25 are arranged outside the stator 20 to illustrate the coils 25 in the grooves 22. A first coil 25 is wound around a tooth 23 such that two conductor sections 32 are arranged in a first groove 22 and one conductor section 31 is arranged in a second groove 22. One second coil 25 is wound around one tooth 23 such that two conductor sections 32 are arranged in the same groove 22 as the one conductor section 32 of the first coil 25. A third conductor section 32 of the second coil 25 is arranged in a third groove 22. The remaining coils 25 are arranged as shown, by way of example, for the first and the second coil 25.

(24) FIG. 5 shows a schematic representation of the stator winding 24 according to the embodiment shown in FIG. 4. The stator 20 has a plurality of coils 25. As shown in FIG. 4, the coils 25 each have three conductor sections 32. In each case, two conductor sections 32 of one coil 25 are arranged in the same groove 22 as one conductor section 32 of a further coil 25. The coils 25 are electrically connected to the short-circuit means 28 on the first side 26. On the second side 27, each of the coils 25 is connected to a power supply unit 31, which can be a half-bridge. For example, each of the power supply units 31 can have two switches 36 as shown for one of the power supply units 31. The power supply units 31 are electrically connected to a power supply 33 of the electric machine 21.

(25) FIG. 6 shows a schematic illustration of the stator winding 24 according to a further embodiment. In contrast to the embodiment shown in FIGS. 4 and 5, in FIG. 6, each of the coils 25 has two conductor sections 32. Each of the coils 25 is electrically connected to the short-circuit means 28 on the first side 26 and to a power supply unit 31.

(26) FIGS. 7A, 7B, 8A and 8B show schematically that individual conductor sections 32 of each coil 25 can be considered separately for the calculation of the magnetomotive force in an embodiment of the stator 20.

(27) FIG. 7A shows a section of a cross-section through the stator 20 projected in a plane. The stator 20 has a plurality of teeth 23, around each of which one coil 25 is wound. For calculating the magnetomotive force of a rotary field generated by the stator winding 24, the coils 25 in FIG. 7A have an even number of conductor sections 32 and thus only a portion of the total number of conductor sections 32. The last conductor section 32 not shown in FIG. 7A is shown separately in FIG. 8A for calculating the magnetomotive force. In FIG. 7A, the distance between two grooves 22 corresponds to the angle φ between two electrical phases of the stator winding 24.

(28) The proportion F1 of the conductor sections 32 shown in FIG. 7A to the magnetomotive force F of a rotary field generated by the stator winding 24 can be given as follows:

(29) $F_1\left(x,t\right)=\frac{m}{2}\frac{2N\hat{I}}{\pi }\underset{v}{.Math.}\frac{1}{v}\xi \cos \left(\omega t-\mathrm{vx}-\left(p-v\right)\phi \right)$

(30) In this case, x specifies the position along the circumference of the stator 20, t specifies the time, m specifies the number of electrical phases, N specifies the number of conductor sections 32, Î specifies the amplitude of the respective phase current, ξ specifies the coil winding factor and ω specifies the frequency of the phase current.

(31) The phase current ik is given by:

(32) $\begin{array}{cc}{i}_k=\hat{I}\cos \left(\omega t-p\left(k-1\right)\frac{2\pi }{m}\right)& \left(1\right)\end{array}$

(33) The harmonic number v is given by:
v=m*g+p
wherein g is an integer. This means that the magnetomotive force F1 can have harmonic components of even and odd order.

(34) The coil winding factor ξ is given by:

(35) $\xi =\sin \left(\frac{v\pi }{m}\right)$
p is the number of pole pairs and a variable parameter which can be calculated via the number of stator grooves Q and can assume the following values:

(36) $p=\{\begin{array}{cc}1,2,\mathrm{.Math.},\frac{Q+1}{2}-1,& \mathrm{for}Q\mathrm{being}\mathrm{an}\mathrm{odd}\mathrm{number}\\ 1,2,\mathrm{.Math.},\frac{Q}{2}-1,& \mathrm{for}Q\mathrm{being}\mathrm{an}\mathrm{even}\mathrm{number}\end{array}$

(37) FIG. 7B shows furthermore that a winding function θ can be specified. The position x along the circumference of the stator 20 is specified in radians on the x-axis. The amplitude of the winding function θ is plotted on the y-axis. An example is a coil 25 having two conductor sections 32, which are indicated by the plus and minus signs. The conductor sections 32 are respectively arranged at the angles −φ/2 and φ/2. The positive amplitude of the winding function θ is given by:

(38) ${\Theta }_{+}=N\left(1-\frac{\phi }{2\pi }\right)$

(39) The negative amplitude of the winding function θ is given by:

(40) ${\Theta }_{-}=N\frac{\phi }{2\pi }$

(41) In FIG. 8A, analogous to FIG. 7A, a detail of a cross-section through the stator 20 is shown projected in a plane. In this case, the additional conductor section 32 is shown in the case where the coils 25 on a first side 26 of each tooth 23 have a greater number of conductor sections 32 by 1 than on a second side of each tooth 23. The conductor sections 32 point in this case into the image plane. The total magnetomotive force F of a rotary field generated by the stator winding 24 can be determined by the sum of the magnetomotive force F1 shown in FIG. 7A and a magnetomotive force F2 of the conductor sections 32 shown in FIG. 8A. The total magnetomotive force F thus relates to a stator winding 24 as shown, for example, with the embodiment in FIG. 5.

(42) The proportion F2 of the conductor sections 32 shown in FIG. 8A to the magnetomotive force F of a rotary field generated by the stator winding 24 can be given as follows:

(43) $F_2\left(x,t\right)=\frac{m}{2}\frac{\hat{I}}{\pi }\underset{v}{.Math.}\frac{1}{v}\sin \left(\omega t-v\left(x+\frac{\phi }{2}\right)-\left(p-v\right)\phi \right)$

(44) Thus, the total magnetomotive force F is given by:
F=F1+F2

(45) FIG. 8B, analogous to FIG. 7B, shows the winding function θ for the conductor sections 32 shown in FIG. 8A. The position x along the circumference of the stator 20 is specified in radians on the x-axis. The amplitude of the winding function θ is plotted on the y-axis. A conductor section 32, which is indicated by the cross, is shown by way of example.

(46) FIG. 9A shows simulations of the magnetomotive force for a stator 20 described here according to an embodiment and for a further stator. In the upper diagram, the angle φ along the circumference of the stator 20 is plotted on the x-axis in radians. The section shown thus corresponds to a cycle of 2π around the circumference of the stator 20. The magnetomotive force normalized to 1 is plotted on the y-axis. The curve A shows the magnetomotive force for a stator 20 according to an embodiment. The curve B shows the magnetomotive force for a stator in which the stator winding is formed by individual electrically conductive bars. One such stator is shown by way of example in FIG. 18A. The number of electrical phases is 18 for both stators of FIG. 9A. In the embodiment of the stator 20, the number of conductor sections 32 for each of the coils 25 on a first side 26 of each coil 25 is two and is one on a second side 27 of each coil 25. This means that each of the coils 25 has a total of three conductor sections 32. This embodiment is shown in FIG. 5 by way of example. In addition, the number of pole pairs for both stators shown in FIG. 9A is 1. The upper diagram in FIG. 9A shows that with a stator 20 described here, a magnetomotive force having a greater amplitude can be generated than with a stator in which the stator winding is formed by individual electrically conductive bars. In addition, both stators are designed to generate a rotary field.

(47) The harmonic components of the magnetomotive force shown in the upper diagram are plotted on the x-axis in the lower diagram in FIG. 9A. The magnetomotive force normalized to 1 is plotted on the y-axis. Cases A and B correspond to those described with the upper diagram in FIG. 9A. In both stators, the magnetomotive force has a fundamental wave (p=1) and two further harmonic components, wherein the amplitudes of the two further harmonic components are significantly reduced with respect to the fundamental wave. It is further shown that the amplitude of the magnetomotive force is greater for a stator 20 described here than for a stator in which the stator winding is formed by individual electrically conductive bars.

(48) FIG. 9B shows the magnetomotive force for the two different stators as described with FIG. 9A for rotary fields having two pole pairs (p=2). In both described stators, the number of pole pairs of the generated rotary field can be changed by changing the phase currents, without it being necessary to change the structure of the respective stator. As described for FIG. 9A, in the upper diagram in FIG. 9B, the magnetomotive force is plotted in radians against the angle φ along the circumference of the stator 20 and in the lower diagram against the harmonic components. Even in the case of two pole pairs, curve A has a greater amplitude than curve B. For both stators, the magnetomotive force has a harmonic component of order 2 and a further harmonic component of order 16, wherein the amplitude of the harmonic component of order 16 is significantly smaller than the amplitude of the harmonic component of order 2.

(49) FIG. 9C shows the magnetomotive force for the two different stators as described with FIG. 9A for a number of three pole pairs of the rotary field. As described for FIG. 9A, in the upper diagram in FIG. 9C, the magnetomotive force is plotted in radians against the angle φ along the circumference of the stator 20 and in the lower diagram against the harmonic components. Even in the case of three pole pairs, curve A, at least in places, has a greater amplitude than curve B. For both stators, the magnetomotive force has a harmonic component of order 3 and a further harmonic component of order 15, wherein the amplitude of the harmonic component of order 15 is significantly smaller than the amplitude of the harmonic component of order 3. For the stator 20 according to an embodiment described here, the magnetomotive force has further harmonic components with very small amplitude.

(50) Thus, according to an embodiment, the stator 20 described here has a greater magnetomotive force for each of the three pairs of pole pairs shown than a stator in which the stator winding is formed by individual electrically conductive bars. In addition, for the stator 20 described here, the power density of the rotary field generated increases with increasing number of pole pairs.

(51) FIG. 10 shows the magnetomotive force for the two different stators as described with FIG. 9A. The magnetomotive force is shown for the case where two rotary fields having the numbers of pole pairs of 1 and 2 are simultaneously generated by the respective stator. As described for FIG. 9A, in the upper diagram in FIG. 10, the magnetomotive force is plotted in radians against the angle φ along the circumference of the stator 20 and in the lower diagram against the harmonic components. Also in this case, curve A has a greater amplitude than curve B. The lower diagram shows that for both stators, the magnetomotive force has harmonic components of order 1 and 2 and further harmonic components with significantly lower amplitude.

(52) In the case where a stator 20 described here is designed to generate at least two rotary fields having different numbers of pole pairs, the proportions for the different numbers of pole pairs are added to the magnetomotive force.

(53) In this case, the components F1 and F2 of the magnetomotive force are given as follows:

(54) $F_1\left(x,t\right)=\frac{m}{2}\frac{2N}{\pi }\underset{j}{.Math.}\underset{v}{.Math.}\frac{{\hat{I}}_i}{v}\xi \cos \left({\omega }_{j}t-v_{j}x-\left(p_j-v_j\right)\phi \right)$$F_2\left(x,t\right)=\frac{m}{2\pi }\underset{j}{.Math.}\underset{v}{.Math.}\frac{{\hat{I}}_j}{v}\sin \left({\omega }_{j}t-v_j\left(x+\frac{\phi }{2}\right)-\left(p_j-v_j\right)\phi \right)$
wherein for j each of the numbers of pole pairs is used. This means that the amplitude, the frequency and the direction of rotation can be controlled or adjusted separately for each of the numbers of pole pairs.

(55) FIGS. 11A and 11B show two further embodiments of the stator 20. Since the number of the grooves 22 in the stator 20 is at least three and in addition is freely selectable, as shown in FIGS. 11A and 11B, the number of grooves 22 can be ten, for example.

(56) In the embodiment in FIG. 11A, one coil 25 is wound around every second tooth 23 of the stator 20. As in FIG. 1, the winding direction of the coils 25 is specified by plus and minus signs. Thus, in each groove 22 are arranged only conductor sections 32 or one conductor section 32 of only one coil 25. Therefore, it is not necessary to electrically insulate conductor sections 32 of different coils 25 from each other within one groove 22. Each of the coils 25 is connected to a power supply unit 31 of its own.

(57) In the embodiment in FIG. 11B, a coil 25 is wound around each tooth 23 of the stator 20. Thus, in each groove

(58) 22 are arranged conductor sections 32 or one conductor section 32 of two coils 25 in each case. Each of the coils 25 is connected to a power supply unit 31 of its own.

(59) FIG. 12 shows the winding factors for various embodiments of the stator 20. In this case, the number of poles of the rotary field generated by the stator 20 are specified in the horizontal direction with the values 2-20. In the vertical direction, the values 4-18 specify the number of electrical phases of the stator 20. The table specifies the winding factors for the respective combinations. The coils 25 are arranged as shown in FIG. 11B in each of the embodiments of the stator 20. This means that one coil 25 is wound around each tooth 23 of the stator 20. The table in FIG. 12 shows that winding factors of up to 99.6% can be achieved with various embodiments of the stator 20.

(60) FIG. 13A plots a compensation component by way of example. In this case, the angle φ along the circumference of the stator 20 is plotted on the x-axis in radians, and the amplitude of the respective harmonic component is normalized to 1 on the y-axis. The continuous line corresponds to the magnetic force of a harmonic component of a rotary field of order 2 generated by the stator 20. Rotary fields generated by a stator 20 described here can have several harmonic components. Some of the harmonic components can be undesirable because, for example, they contribute to vibrations, oscillations or noise development during operation of the electric machine 21 and at least in some cases do not contribute to the usable torque. A harmonic component can contribute to vibrations or noise development during operation of the electric machine 21 if the rotational frequency of the harmonic component is similar to or equal to the fundamental frequency of a vibration mode in the electric machine 21. In most cases, this only applies to low order harmonic components, since the fundamental frequencies of higher order vibration modes are often at rotational frequencies which are greater than a maximum rotational frequency achievable by the electric machine 21. Therefore, the harmonic component of order 2 is shown by way of example in FIG. 13A. At certain rotational frequencies, that is, at certain rotational speeds of the rotor 29, the harmonic component of order 2 can contribute to vibrations and noise development in the electric machine 21. The harmonic component of order 2 can be at least partially compensated with an additionally generated compensation signal.

(61) A harmonic component of order m of the magnetic force can, for example, be given by:
f.sub.m(x,t)= cos(mx+ω.sub.mt−φ.sub.m)

(62) It is the amplitude of the force density with:

(63) $=\frac{1}{2{\mu }_0}$

(64) Wherein and specify the magnetic flux densities of the harmonic components v.sub.1 and v.sub.2.

(65) In order for a harmonic component of order m to be compensated by generating a compensation signal, the compensation signal in the stator must generate a further harmonic component, namely the compensation component. In order for the compensation component to be able to compensate for the harmonic component of order m, it must be true that the amplitude of the compensation component corresponds to the amplitude of the harmonic component of order m and that both signals are out of phase with each another by 180°.

(66) FIG. 13A shows a compensation component by the dashed line. The compensation component and the harmonic component of order 2 are phase shifted to each other by an angle of 45°. In this case, the compensation component cannot completely compensate for the harmonic component of order 2.

(67) FIG. 13B shows the harmonic component of order 2 of FIG. 13A. The axes are the same as in FIG. 13A. A compensation component is shown with the dashed line, which component is phase-shifted by 180° to the harmonic component of order 2. In this case, the harmonic component of order 2 can be completely compensated by the compensation component. The compensation component can thus be regarded as a further generated harmonic component of order 2, which, due to the phase shift of 180°, is designed to compensate for the undesired harmonic component of order 2. It is also possible that a harmonic component of the magnetic force induced by a rotary field is undesirable because of problems other than the occurrence of vibrations or noise, and is compensated for by a compensation component.

(68) FIG. 14 shows a schematic structure of an embodiment of an activation unit 40 having a compensation unit 30. The activation unit 40 is connected to the electric machine 21. The stator of the electric machine 21 can be driven via a control unit 34. For example, the phase currents, the frequency and the load angle can be set via the control unit 34. In addition, the number of pole pairs of a rotary field to be generated can be adjusted. The adjustability of various parameters is represented by the four arrows. The control unit 34 is connected to a converter 35. The converter 35 can be, for example, an inverter. The converter 35 comprises a plurality of outputs 37. Each of the outputs 37 can be connected to a respective input 38 of the electric machine 21. Thus, each of the electrical phases of the stator 20 can be driven separately.

(69) The activation unit 40 further has a compensation unit 30. The compensation unit 30 is designed to generate compensation signals for the at least partial compensation of an undesirable component of a magnetic force, wherein the magnetic force is induced by a rotary field generated by the stator 20 during operation of the electric machine. Parameters of the compensation signals can be set via the compensation unit 30, such as, for example, the amplitude, the frequency, the load angle or the order of a compensation component to be generated. The adjustability of various parameters is represented by the five arrows. The compensation unit 30 is further designed to generate the compensation signals at predefinable operating points of the electric machine 21. In these cases, the compensation signals and the signals of the control unit 34 are added to drive the electrical phases. This means that the respective compensation signal is superposed with the respective phase current for each electrical phase. The electrical phases of the stator 20 are fed with the superposition of these two signals from the converter 35. The predefinable operating points can be, for example, rotational speeds at which vibrations or undesired noises occur. These predefinable operating points can be determined, for example, on a test bench. Advantageously, the compensation signals are thus only generated when they are needed.

(70) The activation unit 40 comprises the control unit 34, the compensation unit 30 and the converter 35.

(71) FIG. 15 shows a cross-section through an embodiment of the electric machine 21. The electric machine 21 has a stator 20 and a rotor 29 rotatably mounted to the stator. The stator 20 of the electric machine 21 has 11 grooves 22. One coil 25 of the stator winding 24 is wound around each of the teeth 23 of the stator 20. The grooves 22 have openings to an inside of the stator 20. The rotor 29 is arranged on the inside of the stator 20. The rotor 29 is thus arranged in the stator 20. The rotor 29 has ten permanent magnets. The electric machine 21 can be a permanent magnet synchronous motor.

(72) FIG. 16 shows the radial component of the magnetic force density for the embodiment of the electric machine 21 shown in FIG. 15. The angle along the circumference of the stator 20 is plotted in degrees in the upper diagram on the x-axis. The radial component of the force density is plotted on the y-axis in kN/m2. In this case, the radial directions are those directions that run parallel to the cross-section or a radius of the stator 20. The rotary field generated by the stator 20 during operation of the electric machine 21 has ten poles. The order of the harmonic components of the radial component of the force density is plotted on the x-axis in the lower diagram. The radial component of the force density is plotted on the y-axis in kN/m2. The harmonic component of order 0 has the largest amplitude. In addition, there are harmonic components of orders 10 and 11. However, in most cases, these only lead to undesirable vibrations or noise developments at rotational speeds greater than the usual maximum rotational speeds. In contrast, the harmonic component of order 1 could produce undesirable vibrations or noise developments at certain rotational speeds.

(73) FIG. 17 shows by way of example the compensation of an undesired component of the magnetic force of order 1 of FIG. 16. The phase current ik of the harmonic component of order 1 results from equation (1). The phase current is superimposed with a compensation signal. The index 1 represents the phase current for generating the harmonic component of the magnetic force of order 1 and the index 2 represents the compensation signal:

(74) 0$i_k=\cos \left({\omega }_{1}t-p_1\left(k-1\right)\frac{2k}{\pi }+{\delta }_1\right)+\cos \left({\omega }_{2}t-p_2\left(k-1\right)\frac{2\pi }{m}+{\delta }_2\right)$
wherein δ is the load angle.

(75) The ratio of the effective values of the phase currents I2/I1 is plotted on the x-axis in FIG. 17. On the y-axis, the load angle is plotted in degrees, and on the z-axis is plotted the ratio of the portion of the harmonic component of order 1 of the radial component of the magnetic force density with compensation to the portion of the harmonic component of order 1 of the radial component of the magnetic force density without compensation. This means that about 80% of the undesired radial force component of order 1 can be compensated for in the event that the ratio of the effective values of the phase currents is about 0.6 and the load angle is about 50°.

(76) FIGS. 18A and 18B show a stator 20 for an electric machine 21. The stator 20 and the electric machine 21 are not embodiments. The stator 20 is shown with a stator winding 24 in FIG. 18A. The stator 20 has a plurality of grooves 22 in which the stator winding 24 is arranged. The stator winding 24 is formed by individual electrically conductive bars 39, wherein in each case one of the bars 39 is arranged in one groove 22. The bars 39 are electrically connected to each other via a short-circuit means 28 on a first side 26 of the stator 20.

(77) FIG. 18B shows the stator winding 24 with the short-circuit means 28 and without the stator 20. The bars 39 are arranged along the circumference of the stator 20 and extend parallel to each other.

(78) FIG. 19A shows a winding for a rotor 29 of the electric machine 21. The winding has a structure similar to the stator winding shown in FIG. 5. The rotor 29 has a plurality of coils 25. The coils 25 each have three conductor sections 32. On a first side 26, the coils 25 are electrically connected to a short-circuit means 28. On a second side 27, which faces away from the first side 26, each of the coils is connected to one rectifier 41. The rectifiers 41 are electrically connected to a voltage output 47. The induced voltage can thus be rectified for each of the coils 25.

(79) FIG. 19B shows a cross-section through an embodiment of a rotor 29. The rotor 29 has an excitation winding 42 and a field winding 43.

(80) Furthermore, the rotor 29 has at least three, in this case eight, teeth 23 and at least three, in this case eight, grooves 22. One tooth 23 of the rotor 29 is arranged in each case between two grooves 22 along a circumference of the rotor 29. The excitation winding 42 has at least three coils 25, in this case eight coils 25. The excitation winding 42 is constructed as shown in FIG. 19A. Each of the coils 25 in this case is connected to a rectifier 41 of its own. The field winding 43 also has eight coils 25. The structure of the field winding 43 is shown in FIG. 19D. Such a rotor 29 can be used with a stator 20 described here for a current-excited (self-excited) synchronous machine and/or for a brushless current-excited synchronous machine.

(81) FIG. 19C shows a block diagram for an embodiment of a rotor 29. The rotor 29 can be used for a current-excited synchronous machine and the structure of the rotor 29 is shown in FIG. 19B. The excitation winding 42 having eight coils 25 is constructed as shown in FIG. 19A. The rectifiers 41 form a polyphase rectifier unit 45. The field winding 43 is electrically connected to the rectifier unit 45 via two connections 46.

(82) FIG. 19D shows the structure of an embodiment of the field winding 43. The field winding 43 has eight coils 25, which are connected to each other in series. The field winding 43 is electrically connected to the rectifier unit 45 at the two connections 46 of the field winding 43.