Electric motor

Abstract

An electric motor having stator-side bar windings comprises a plurality of inverters for controlling the bars, wherein: the power components of the inverters are arranged on one or more circuit boards, and the circuit boards form at least one circular or annular structure; the circuit boards are electrically connected by means of a connecting printed circuit board; and the connecting printed circuit board is annular and is plugged onto the circuit boards.

Description

[0001] Description

[0002] electric motor

[0003] The invention relates to an electric motor with a stator-side bar winding.

[0004] Electric motors can have a bar winding on the stator side. The stator has a series of bars as field conductors instead of wound wire conductors. These bars have a low inductance compared to conventional windings. Therefore, a comparatively high current flow is required to generate a given magnetic field.

[0005] However, due to the low inductance of the rods, this high current flow requires only a comparatively low voltage, such as 12 V. This low voltage allows the inverter components used to control the rods to be arranged at close distances from one another. For example, the power electronics components can be arranged on one or more circuit boards located close to the electric motor.

[0006] A particularly advantageous feature is that such an electric motor can be designed in a compact manner so that each field conductor is controlled by its own power components, thus allowing each field conductor to be controlled by its own phase. This allows electric motors with 48, 72, or even 120 field conductors and phases to be constructed compactly.

[0007] The problem is that the large number of power units must be connected to a central controller. Cable connections between a central controller and a large number of power units result in a very complex structure. The object of the invention is to provide an electric motor that eliminates the aforementioned disadvantage, in particular, that has an efficient connection between the controller and the power units.

[0008] This object is achieved by an electric motor having the features specified in claim 1.

[0009] The electric motor according to the invention comprises a stator with a plurality of field conductors configured as bars. Furthermore, the electric motor comprises an inverter with one or more parallel power units for each of the field conductors for controlling them, wherein the inverter comprises a controller for generating control signals for the power units.

[0010] The inverter's output stages are arranged on a plurality of circuit boards. The circuit boards, in turn, are arranged to form at least one circular or ring-shaped structure.

[0011] One or more connectors are arranged on each of the circuit boards for contacting the output stages. A connecting board is connected to the connectors of at least two of the circuit boards of one of the circular or ring-shaped structures.

[0012] Since the circular or ring-shaped structures are constructed from a plurality of circuit boards, it is understood that they are not geometrically precise, and the circular or ring surface does not have to be completely filled. Rather, gaps remain between the circuit boards.

[0013] The connectors can be spring contacts or direct circuit board connectors, for example. They can be a socket, a (built-in) plug, or a screw contact, with the corresponding counterpart being arranged on the connecting board. In the context of this text, the term “output stage” essentially refers to the power semiconductor switches that belong to an AC voltage output. Since the gate driver circuits belonging to the power semiconductor switches are physically separate from the power semiconductor switches in some embodiments of the invention, these are not counted as part of the output stage. The term “power section” refers to the power semiconductor switches together with their respective gate driver circuits. The entirety of the power sections and control system is referred to as an inverter.

[0014] The invention advantageously achieves a particularly simple type of contacting of the electronic components on the circuit boards, in which a large number of cables between the control system and the circuit boards are replaced by a single connecting board per circular or annular structure. If such an electric motor has, for example, 72 phases, i.e. 72 field conductors, and three of these field conductors are controlled by a circuit board, then each circular or annular structure comprises 24 circuit boards. The connecting board, which is expediently connected to the connectors of all the circuit boards, then takes the place of 24 cables to the control system. This board can be connected to the control system with a single cable.

[0015] It is expedient if there is a connecting board for each circular or ring-shaped structure, in particular exactly one connecting board.

[0016] The connecting boards advantageously establish an indirect connection between the controller on the one hand and the output stages, i.e., the power semiconductor switches, on the printed circuit boards on the other. Indirect means that the gate driver circuits for the power semiconductor switches are located in the middle of this connection. The gate driver circuits can be arranged in various ways. Advantageous embodiments of the electric motor according to the invention emerge from the dependent claims. The embodiment of the independent claims can be combined with the features of one of the subclaims or with those of several subclaims. Accordingly, the following additional features can be provided:

[0017] The connecting board is preferably circular or ring-shaped. The ring shape of the connecting board, as with ring-shaped structures, leaves a recess in the center through which air cooling can be achieved.

[0018] The interconnection board is preferably connected to the connectors of all circuit boards in a respective circular or ring-shaped structure. It then connects all circuit boards in the circular or ring-shaped structure to the controller, minimizing the number of required cable connections.

[0019] In an alternative embodiment, the connecting board is ring-sector-shaped. In other words, the connecting board only forms a section of the ring. In this case, it is only connected to some of the circuit boards in a circular or ring-shaped structure. It is expediently designed so that a plurality of identical connecting boards cover the entire ring so that all circuit boards are connected to one of the connecting boards. For smaller electric motors, the center angle can expediently be approximately 180°, 120°, or 90°, which means that 2, 3, or 4 connecting boards are required to contact all circuit boards in a circular or ring-shaped structure. For large electric motors with many phases, the diameter of the circular or ring-shaped structures can be in the meter range.In this case, it may be advantageous to use much smaller center angles, as otherwise the connecting boards would be too large. In this case, the connecting boards can be designed so that they contact two, three or four of the circuit boards, for example. In an electric motor with 120 phases, in which the connecting board contacts three of the circuit boards, the center angle is only approx. 9°. With such connecting boards, the curvature of the circumference is small and a rectangular board can be used instead of a ring-sector-shaped connecting board. Since it is advantageous if the circuit boards are all designed in the same way, it is advantageous if the connectors are nevertheless placed in a ring-like arrangement.

[0020] It goes without saying that the center angle specifications do not need to be exact. The actual center angles can be somewhat smaller, as this allows for some space between the connecting boards while still allowing contact to all circuit boards. While such connecting boards require more control cables than a ring-shaped connecting board, they are significantly easier to install and remove, especially if the electric motor comprises several cooling plates with circuit boards on both sides.

[0021] The number of connecting boards preferably corresponds to the number of circular or annular structures. Therefore, if the circuit boards form two or more circular or annular structures, then preferably a connecting board for each of the circular or annular structures is connected to the connectors of at least two circuit boards of each of the circular or annular structures.

[0022] In certain embodiments, the connecting board is connected to a plurality of printed circuit boards of two different circular or annular structures, these structures then expediently being arranged on two adjacent cooling plates on sides facing each other. The connecting board is plugged into the printed circuit boards of one of the two circular or annular structures by means of connectors. The connecting board can also be plugged into the printed circuit boards of the other circular or annular structure by means of connectors. Alternatively, the connection can also be realized by means of cable connections in order to be able to maintain a more flexible distance from one of the two circular or annular structures and to simplify installation. This configuration can be combined with other embodiments.For example, two concentric and coplanar interconnect boards may be present and connected to the circuit boards of two facing circular or ring-shaped structures to provide control redundancy. The interconnect boards may also be complete rings, ring-sector-shaped interconnect boards, or other shapes.

[0023] Even if the connecting plates are completely annular, the electric motor can comprise two or more connecting plates for each circular or annular structure. These can, for example, have different radii and thus be mounted concentrically and coplanarly on the circular or annular structure.

[0024] A similar design is also possible if the connecting boards are only ring-sector shaped. In this case, too, connecting boards with different radii can be plugged concentrically and coplanarly onto the circular or ring-shaped structure, thus forming two gap-shaped rings.

[0025] In both of the cases mentioned, the connecting boards and circuit boards can be designed so that each of the circuit boards is plugged into exactly one of the connecting boards. In this case, for example, an inner ring can contact every second circuit board or every second phase, and an outer ring can contact the remaining circuit boards or phases. In this case, the connecting boards cover all of the circuit boards, but only contact every second one. They can also be designed so that each of the circuit boards is plugged into two or more connecting boards. In this case, the connecting boards contact all of the covered circuit boards. This can create redundancy, and the failure of the entire motor or a large proportion of it if one connecting board fails can be avoided.

[0026] The central axis of the circular or annular structure or structures may correspond to the motor axis. In other words, this means that the center of each circular or annular structure lies on the motor axis and that each circular or annular structure is arranged perpendicular to the motor axis.

[0027] If the electric motor has several circular or ring-shaped structures, these are preferably arranged parallel to one another and axially offset from one another so that their centers lie on a common central axis.

[0028] The connecting board is preferably arranged parallel to the attached circular or ring-shaped structure, i.e. perpendicular to the central axis, in particular perpendicular to the motor axis.

[0029] In this arrangement of the circular or ring-shaped structures, the field conductors or the current conductors continuing them penetrate the circular or ring-shaped structures in a straight line in a rotationally symmetrical manner. This results in a well-modularized structure in which similar circuit boards can be used and in which contacting each field conductor is particularly simple.

[0030] Furthermore, the field conductors or their continuation current conductors can even act as mechanical supports for the circuit boards, further simplifying the design. The connecting board can include gate driver circuits for the power components. This ensures that the gate driver circuits no longer require their own space on the boards. Accordingly, more space remains on the boards for the power components, simplifying the design of the boards. Furthermore, waste heat generated by the gate driver circuits is removed from the boards, thus simplifying heat dissipation.

[0031] Furthermore, the connection board can also include one or more local control chips that perform control tasks, such as current measurement for a respective power amplifier. The local control chips are each assigned to one or more gate driver circuits and connected to them.

[0032] Alternatively, the gate driver circuits can be arranged on the boards themselves, together with the respective power semiconductor switches. This simplifies the design of the interconnection boards, as they only need to establish a connection between the controller and the boards, and thus the gate driver circuits. For this purpose, the interconnection boards can advantageously include a multiplexer.

[0033] In a further alternative, the gate driver circuits can also be arranged on their own driver boards. These are preferably plugged onto the boards with the power semiconductor switches, with the boards being arranged in a sandwich-like manner in this case, i.e., the driver boards at least partially cover the boards. In this case, the connecting boards can be plugged onto the driver boards or onto the printed circuit boards, i.e., they can have a connection to one of the board types via which signals are transmitted.

[0034] Each phase controlled on a circuit board has a half-bridge made up of two logic switches. A logic switch can comprise a single power semiconductor switch. To allow switching of higher currents, a logic switch can also comprise a plurality of power semiconductor switches, for example, two, three, five, or even more power semiconductor switches connected in parallel.

[0035] A gate driver circuit is preferably designed in such a way that it controls the control terminals (for example gate terminals) of the two logic switches of the half-bridge, i.e. supplies them with current / voltage in such a way that the switching operations required by the control take place and the switches are switched on and off in a manner required by the control.

[0036] If the logic switches of the half-bridge each comprise more than one parallel power semiconductor switch, then the gate driver circuit can be designed to control all of the power semiconductor switches. However, it is also possible to provide more than one gate driver circuit for the control. For example, the number of gate driver circuits can correspond exactly to the number of parallel power semiconductor switches. So if the half-bridge comprises five high-side MOSFETs and five low-side MOSFETs, up to ten gate driver circuits can be present. In this case, for reasons of space, it is advantageous to arrange the gate driver circuits on the driver board or on the connection board.

[0037] The connection board can comprise a multiplexer and other additional circuits such as monitoring, control, amplifier / buffer circuits or communication interfaces and can be designed such that a control signal for a first power section, received from the controller on a first signal line, is routed by the multiplexer to one of several second signal lines, which is connected to the first power section via a spring contact, for example. The multiplexer on the connection board ensures that the controller only needs to be connected to the connection board with a single signal line, which simplifies the design.This is particularly advantageous when the interconnection board connects multiple power modules on a single board, as well as a plurality of parallel-connected power modules to the controller, since in this case, without the multiplexer, a large number of parallel control lines would be required from the controller to the interconnection board. The individual signal line can be a direct electrical line or a connection operating according to a communications standard, such as a USB connection, a LAN connection, an optical connection, or a screw connection.

[0038] The connecting board may include one or more screw connections to one or more of the circular or ring-shaped structures. Screw connections prevent the connecting board from becoming loose due to vibrations and other external factors.

[0039] The interconnect board can be a flexible printed circuit board. Flexible printed circuit boards can deform under mechanical stress. Conductive tracks and other electronic components on such boards retain their electrical function.

[0040] The current conductors can be designed in such a way that they extend the field conductors axially. The current conductors are designed in a similar way to the field conductors of the electric motor, but can, for example, have a different cross-sectional shape. For example, the current conductors can have a round cross-section, while the field conductors have an elongated rectangular cross-section. It is expedient if the current conductors can carry at least the same current as the field conductors. The current conductors and field conductors can be connected via shoes designed for this purpose, which ensure a mechanical and electrical connection. The printed circuit boards can be arranged on at least one cooling plate. The cooling plate can have circuit boards on both sides in order to achieve a high density of electrical components. The cooling plate is preferably a metallic, essentially circular or annular plate.The cooling plate can have heat pipes for heat dissipation or cooling channels for airflow. The cooling plate can also be constructed from two parallel, ring-shaped plates that are screwed together so that a gap remains between them. Active ventilation can then be arranged so that air is drawn in between the plates.

[0041] The cooling plate can be arranged such that the field conductors or current conductors electrically connected to the field conductors are in mechanical operative connection with the cooling plate. For example, the current conductors or field conductors can be designed as a mechanical support for the cooling plate. For this purpose, the cooling plate is preferably arranged perpendicular to the axis of the electrical machine. In this way, the cooling plate with the circuit boards can be arranged at an axial end of the electrical machine in a space-saving manner.

[0042] The printed circuit boards can be circular or ring-sector shaped. Printed circuit boards with this shape are particularly well-suited to assembling into a circle or ring, allowing them to be optimally adapted to the shape of the electrical machine and arranged at one axial end of the machine, while simultaneously achieving a high degree of modularity.

[0043] The power units are preferably designed to generate an alternating voltage with an amplitude of 200 V or less, in particular 100 V or less, in particular 50 V or less. This makes it possible for the components of the power electronics, in particular the power semiconductor switches, to be arranged at small distances from one another in the millimeter range, and thus for a significant number of power semiconductor switches to be arranged in a relatively small space. This makes it possible to provide high currents without requiring too much space and, at the same time, to generate a large number of phases, for example 6, 12, 24, 48, 72 or even 120 phases.

[0044] The field conductors, which are designed as bars, can be solid bars, for example made of copper, but in other designs of the electric motor they can also have subdivisions in the longitudinal direction or be constructed as a bundle of conductors, whereby the general structure as a bar (instead of as a winding) is retained.

[0045] The invention is described and explained in more detail below with reference to the exemplary embodiments shown in the figures. They show schematically:

[0046] Figure 1 shows an electric motor with power components arranged on circuit boards supported by cooling plates in an oblique view,

[0047] Figure 2: Front view of circuit boards arranged on a cooling plate,

[0048] Figure 3 shows a section of the electric motor in an oblique view with cooling plates with printed circuit boards,

[0049] Figure 4 shows a section of the electric motor with cooling plates with circuit boards and connecting boards connected via spring contacts in side view,

[0050] Figures 5 to 7 show a front view of the electric motor with cooling plates with printed circuit boards and connecting boards,

[0051] Figure 8 is a sectional view of a cooling plate with circuit board, driver board and connection board. Figure 1 is an isometric view of an electric motor 10 which is an exemplary embodiment of the invention. The electric motor 10 comprises a stator 11 and a rotor which is essentially arranged in the stator 11 and is not visible in Figure 1. The rotor is connected in a rotationally fixed manner to a shaft which is also not shown in Figure 1. The rotor is set in rotation about an axis 9 by electromagnetic interaction of the rotor with the energized stator 11. The rotor is separated from the stator 11 by an air gap. In other embodiments, the electric motor 10 can also be an external rotor motor or a bell-shaped armature motor.

[0052] The stator 11 comprises, as field conductors, a plurality of rigid and straight conductor bars 12. These conductor bars 12 are connected to one another on the end face 13 facing away in Figure 1 via a short-circuit ring. On the rear side 14 of the electric motor 10, the conductor bars 12 are individually fed by associated inverter modules. Since the electric motor 10 is operated at low voltages due to the conductor bars 12, the inverter modules can be arranged relatively close together on printed circuit boards 15, together with other electronic components (DC-DC converter, rectifier). In this example, the printed circuit boards 15 are ring-sector-shaped and many individual printed circuit boards 15 together form a ring-shaped circuit board structure.

[0053] While the examples assume that the circuit boards 15 carry at least the power components of inverters, it is also possible that some of the circuit boards 15 carry rectifiers and DC / DC converters.

[0054] Figure 2 shows a plan view of such a circuit board structure. The number of circuit boards shown in Figure 2 has been reduced compared to the illustration in Figure 1 and is shown in a greatly simplified manner for better clarity. The actual number of such circuit boards 15 depends on the specific design of the electric motor 10, in particular the number of conductor bars 12. Each of the circuit boards 15 comprises a plurality of semiconductor switches 422. The semiconductor switches 422 together form power sections of inverters which provide an alternating voltage for the conductor bars 12.

[0055] Furthermore, some or all of the circuit boards 15 can comprise driver circuits and other electronic components such as capacitors, not shown in the figures. The semiconductor switches 422 are power semiconductors, such as IGBTs, MOSFETs or JFETs, and can additionally comprise diodes not shown, depending on the wiring. The semiconductor switches 422 are wired as half-bridges, for example. A capacitor not shown can represent, for example, an intermediate circuit capacitor of the half-bridges. The semiconductor switches 422 of a circuit board 15 can be assigned to a single phase. In an electric motor 10 with a large number of field conductors 12 and a corresponding number of phases, it is advantageous if one circuit board 15 carries the power components for several phases.

[0056] The printed circuit boards 15 further comprise contact points 421 to which the conductor bars 12 are connected. The printed circuit boards 15 are supported by disc-shaped cooling plates 16, wherein the cooling plates 16 can be covered with printed circuit boards 15 on both sides for better space utilization.

[0057] Since relatively high currents are required in the conductor bars of the electric motor 10, several power units are preferably connected in parallel to supply power to them. This can be achieved, for example, by the six circuit board structures shown in Figure 1 on three cooling plates 16 all being connected in the same way to the conductor bars 12 and thus being electrically connected in parallel. This takes advantage of the fact that the conductor bars 12 or connecting elements 18 to the conductor bars 12 penetrate the cooling plates 16 and thus also the printed circuit boards 15 in the same way at the contact points or, in the case of the outermost cooling plate 16, at least contact them.

[0058] Figure 3 shows a sectional view of the electric motor 10 in an oblique view. Here it can be seen that the connecting elements 18 mechanically support and penetrate the three cooling plates 16. The connecting elements 18 are connected to the conductor bars 12 via shoes 17. The output stages, which are located on the circuit boards 15 in the areas in which one of the connecting elements 18 penetrates a cooling plate 16, are connected in parallel and together provide the current for the conductor bar 12. In the structure shown in Figure 3 it can be seen that two of the connecting elements 18 each pass through a circuit board 15. Thus each of the circuit boards carries the output stages for two phases of the electric motor 10. In other variants for the electric motor 10, a single circuit board 15 can also carry just one phase or three or more phases, with the same number of connecting elements 18 passing through the circuit board 15.

[0059] Figure 4 shows a side view of a section of the electric motor 10. Figure 4 shows eight printed circuit boards 15 arranged on two cooling plates 16. Furthermore, Figure 4 shows four connecting boards 32, each connecting two of the printed circuit boards 15. The connecting boards 32 are connected parallel to the printed circuit boards by means of spring contacts 33 to sockets 34 of a respective printed circuit board 15. Each of the connecting boards 32 further comprises a socket 35.

[0060] The socket 35 is provided for a cable connection 36 to the controller. It can lead out the signal lines in parallel, for example as a socket strip for a direct board connector or as a socket for a parallel interface cable. Another possibility is for the socket 35 to be a USB or LAN (RJ45) socket. Other connection types such as optical connections are also possible. The connecting board 32, 61 can also have electronic components not shown, for example for controlling the socket 35 or for other signal conditioning, signal processing or communication.

[0061] The arrangement in Figure 4 corresponds to that of Figures 1 to 3. Therefore, the sectional view of Figure 4 covers exactly eight circuit boards 15 of the ring structure formed by the circuit boards 15. The connecting boards 32 shown in Figure 4 are ring-shaped and are also connected to the circuit boards 15 not shown.

[0062] Figure 5 shows the same structure in a front view. In Figure 5 it can be seen that the circuit boards 15 form a ring structure and that the connecting board 32 is ring-shaped. According to Figure 5, twelve circuit boards 15 are arranged on the front of the cooling plate 16. With both sides of the cooling plates 16 and two cooling plates used as shown in Figure 4, the electric motor 10 therefore comprises 48 circuit boards 15 which are connected to a control board by means of four connecting boards 32. Only four cable connections 36 are necessary for this connection.

[0063] In the front view of Figure 5, only the front of a cooling plate 16 and only one connecting board 32 are shown, all other elements are hidden.

[0064] For simplicity, the figures show individual spring contacts 33 and sockets 34. However, in each case, this can also refer to multiple actual signal lines. The sockets 34 can therefore actually be socket strips, and the spring contacts 33 can be corresponding plug strips. It is also irrelevant which elements carry sockets 34 or spring contacts 33; these are interchangeable.

[0065] In the example of a ring-shaped connecting board 32 according to Figures 4 and 5, all circuit boards 15 of a ring-shaped structure are connected to the respective connecting board 32 and via this to the controller. In this example, the connecting board 32 has a gate driver circuit 72 and a local control chip 73 for each of the connected circuit boards 15. These are supplied by a multiplexer 93 with the signals received via the cable connection 36. Furthermore, the connecting board 32 has electrical connections between the elements, which are not shown for reasons of clarity.

[0066] Figure 6 shows a front view of an alternative embodiment. As in Figure 5, the circuit boards 15 here also form a ring structure. In contrast to Figure 5, however, here the connection board is divided into three ring-sector-shaped connection boards 61. Each of the ring-sector-shaped connection boards 61 comprises a socket 35 for a cable connection 36 for the control and a multiplexer 93 for splitting the incoming signals. Otherwise, the ring-sector-shaped connection boards 61 comprise those gate driver circuits 72 and local control chips 73 which are assigned to the respectively connected circuit boards 15. The ring-sector-shaped connection boards 61 each have a central angle of slightly less than 120°, thus each making up approximately one third of a circle.Thus, by combining three of the ring-sector-shaped connecting boards 61, all circuit boards 15 of the ring-shaped structure are connected to the controller. In addition to the example shown, the ring-sector-shaped connecting boards 61 could also be designed with center angles of 180° or 90°, whereby the circuit boards 15 would then be contacted by means of two or four of the connecting boards 61.

[0067] With three ring-sector-shaped connecting boards 61, each with its own cable connection 36 and two cooling plates occupied on both sides, this results in a total of 12 cable connections 36 between the connecting boards 61 and the controller. Another possible embodiment is shown in Figure 7. The connecting board 75 is ring-shaped, but in contrast to the previous examples, does not contain the gate driver circuits 72 and local control chips 73, but only the socket 35, the multiplexer 93 and the spring contacts 33 to the printed circuit boards 15. In addition, the connecting board 75 can also have other electronic components for signal conditioning, signal processing and communication. The spring contacts 33 are connected to the multiplexer 93 via signal lines 82. For the sake of clarity, the signal lines are shown as simple lines, but each one can comprise several separate electrical connections.The connecting board 75 thus serves as a signal distributor. The gate driver circuits 72 and local control chips 73 are arranged on the printed circuit boards 15 in this embodiment (not shown in Figure 7).

[0068] In addition to the possibility of connecting the connecting boards 75 directly to the circuit boards 15 that carry the output stages, there is also a further embodiment, which is shown in a sectional view in Figure 8. The circuit board 15 arranged on a cooling plate 16 carries an output stage of the inverter, simplified as a power semiconductor switch 71. A driver board 70 carries the gate driver circuit 72 and a local control chip 73. Connectors 74 transmit the signals between the circuit board 15 and the driver board 70. The spring contact 33 is arranged on the driver board 70 in this embodiment. The connecting board 75 is therefore plugged onto the driver board 70 in this embodiment, as shown. Reference symbol

[0069] 9 Motor axle

[0070] 10 Electric motor

[0071] 11 Stator

[0072] 12 conductor bars

[0073] 13 Front side

[0074] 14 Back

[0075] 15 circuit boards

[0076] 16 Cooling plate

[0077] 17 shoe

[0078] 18 Connecting element

[0079] 32 , 61 , 75 connection board

[0080] 33 spring contact

[0081] 34 , 35 socket

[0082] 36 Cable connection

[0083] 61 ring sector-shaped connection board

[0084] 70 driver board

[0085] 71 power semiconductor chip

[0086] 72 Gate driver circuit

[0087] 73 local control chip

[0088] 82 Signal line

[0089] 93 multiplexers

[0090] 421 contact points

[0091] 422 semiconductor switches

Claims

Patent claims 1. Electric motor (10) with: - a stator (11) with a plurality of field conductors (12) designed as a bar, - an inverter with one or more parallel power units for each of the field conductors (12) for controlling them, wherein the inverter comprises a controller for generating control signals for the power units, wherein - the output stages of the inverter are arranged on a plurality of printed circuit boards (15), - the printed circuit boards (15) are arranged so that they form one or more circular or ring-shaped structures, - one or more connectors (33) are arranged on each of the printed circuit boards (15) for contacting the output stages, - a connecting board (32, 61, 75) is plugged into the connectors (33) of at least two of the printed circuit boards (15) of one of the circular or ring-shaped structures.

2. Electric motor (10) according to claim 1, wherein the connecting board (32, 61, 75) is plugged into the connectors (33) of all circuit boards (15) of a circular or annular structure.

3. Electric motor (10) according to claim 1 or 2, wherein the connecting board (32, 61, 75) is ring-shaped or ring-sector-shaped.

4. Electric motor (10) according to one of the preceding claims, in which the printed circuit boards (15) form two or more circular or annular structures and for each of the circular or annular structures a connecting board (32, 61, 75) is plugged into the connectors (33) of at least two printed circuit boards (15) of each of the circular or annular structures.

5. Electric motor (10) according to claim 4, wherein the circular or annular structures are arranged parallel to each other and axially offset from each other so that their centers lie on a common central axis, 6. Electric motor (10) according to claim 5, wherein the axis of the circular or annular structures corresponds to the motor axis (9).

7. Electric motor (10) according to one of claims 4 to 6, wherein the circular or annular structures have the same diameter.

8. Electric motor (10) according to one of the preceding claims, wherein the connecting board (32, 61, 75) is arranged parallel to the attached circular or annular structure.

9. Electric motor (10) according to one of the preceding claims, wherein the connecting board (32, 61, 75) comprises gate driver circuits (72) for the output stages of the attached circular or ring-shaped structure.

10. Electric motor (10) according to one of the preceding claims, in which the connecting board (32, 61, 75) comprises a multiplexer (93) and is designed to route a control signal received from the controller to one of several signal lines in such a way that it is fed to the power section to which the control signal applies.

11. Electric motor (10) according to one of the preceding claims, wherein the connecting board (32, 61, 75) comprises one or more screw connections with the circular or annular structure.

12. Electric motor (10) according to one of the preceding claims, in which the printed circuit boards (15) are arranged on at least one cooling plate (16) and in which the cooling plate (16) is arranged such that the field conductors (12) or with the field conductors (12) electrically connected current conductors (18) are in mechanical operative connection with the cooling plate, in particular are designed as a mechanical support for the cooling plate (16).

13. Electric motor (10) according to one of the preceding claims, in which the printed circuit boards (15) are designed in the shape of a circular sector or a ring sector.

14. Electric motor (10) according to one of the preceding claims, designed to control the field conductors (12) with at least 6 phases.

15. Electric motor (10) according to one of the preceding claims, in which the inverters are designed to generate an alternating voltage with an amplitude of 100 V or less, in particular 50 V or less, in particular 20 V or less.

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