Electrical machine and method for operating an electrical machine

Abstract

An electric machine (1) comprising a stator (2) and a rotor (3) rotatably mounted about an axis of rotation (4) relative to the stator (2), wherein the rotor (3) has a coolant channel (16) for flow with a coolant and a rotor winding (8) for generating a rotor magnetic field, which is connected to an alternating current source via a rectifier device (9) arranged on the rotor (3), wherein the rectifier device (9) is arranged in a heat-transferring manner on a rotor body (12) of the rotor (3) which receives the coolant channel (16), so that the rectifier device (9) is thermally connected to the coolant channel (16) via the rotor body (12), characterized in that the rectifier device (9) has a circuit board (10) which is in contact with the rotor body (12) via a heat-conducting element (13),wherein the rectifier device (9) is arranged on a rotor wall (14) of the rotor body (12) and the rotor winding (8) is arranged on a side of the rotor wall (14) facing away from the rectifier device (9), wherein a projection (15) extends from the rotor wall (14) on which a secondary winding (7) of the rotor (3) is arranged, cooperating with a primary winding (6) of the stator (2) for inductive energy transfer, and the rectifier device (9) is electrically connected to the secondary winding (7), wherein a main extension plane of the circuit board (10) is angled relative to the axis of rotation (4).

Description

[0001] The invention relates to an electric machine with a stator and a rotor rotatably mounted about an axis of rotation relative to the stator, wherein the rotor has a coolant channel for flowing with a coolant and a rotor winding for generating a rotor magnetic field, which is connected to an alternating current source via a rectifier device arranged on the rotor, wherein the rectifier device is arranged in a heat-transferring manner on a rotor body of the rotor which accommodates the coolant channel, so that the rectifier device is thermally connected to the coolant channel via the rotor body. The invention further relates to a method for operating an electric machine.

[0002] For example, the prior art document DE 10 2021 212 017 A1 is known. This document relates to a rotor assembly for an inductively excited synchronous machine. The rotor assembly comprises a hollow shaft rotatable about an axis of rotation, a rotor, and a secondary-side circuit of an energy transformer. The secondary-side circuit includes a rectifier with a printed circuit board and at least one electrical component, and a secondary coil. The rectifier is oriented transversely to the axis of rotation and is arranged in a cavity of the hollow shaft in a rotationally fixed manner.

[0003] The German patent application DE 10 2021 212 012 B3 relates to a rotor for a separately excited synchronous machine with a rotor winding arranged on a rotor shaft and a rectifier. To reduce the load on the rotor of a rotary transformer and to minimize interference, the rectifier and a secondary coil are arranged inside the hollow rotor shaft.

[0004] The prior art documents DE 10 2022 201 589 A1, DE 10 2020 216 485 A1 and DE 38 31 551 C2 are also known.

[0005] The object of the invention is to propose an electric machine which has advantages over known electric machines, in particular ensuring particularly effective cooling of the rectifier device while simultaneously being easy to manufacture and having a high durability.

[0006] This is achieved according to the invention with an electric machine having the features of claim 1. It is provided that the rectifier device comprises a printed circuit board which rests against the rotor body via a heat-conducting element, wherein the rectifier device is arranged on a rotor wall of the rotor body and the rotor winding is arranged on a side of the rotor wall facing away from the rectifier device, wherein a projection extends from the rotor wall on which a secondary winding of the rotor, cooperating with a primary winding of the stator for inductive energy transfer, is arranged, and the rectifier device is electrically connected to the secondary winding, wherein a main extension plane of the printed circuit board is angled relative to the axis of rotation.

[0007] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible.

[0008] The electric machine is a separately excited electric machine and can be operated either as an electric motor or as a generator. Preferably, the electric machine serves as a traction machine for a motor vehicle, i.e., as a drive unit of the vehicle's drive system. The electric machine generally comprises a stator and a rotor, which is rotatably mounted around the axis of rotation relative to the stator. The stator has a stator winding, which is supplied with electric current at least intermittently to operate the electric machine, thus generating a stator magnetic field.

[0009] The rotor magnetic field serves as the opposing field to the stator magnetic field. This field is generated by the rotor winding, which is supplied with a direct current. The direct current is provided to the rotor winding by means of a rectifier. Due to the direct current being supplied to the rotor winding, heat is generated on or within the rotor, which must be dissipated for reliable operation of the electric machine. For this purpose, the rotor has a coolant channel through which coolant flows, at least intermittently, to cool the rotor. For example, the coolant channel is centered with respect to the axis of rotation or has a longitudinal center axis that is parallel to or coincides with the axis of rotation.

[0010] In known electric machines, the rectifier is either uncooled or requires significant design effort to cool it. In the case of an uncooled rectifier, it can be oversized to reduce its temperature sensitivity, and / or the current supplied to the rotor winding must be limited. However, this reduces the excitation power of the electric machine and consequently its rated power.

[0011] If the permissible temperature of the rectifier is exceeded, the electric machine may fail or even be damaged. It is also known to arrange the rectifier in the coolant channel so that it is directly exposed to the coolant flow. However, this is complex because it compromises the tightness of the coolant channel, and furthermore, the rectifier must be designed to withstand exposure to the coolant.

[0012] For this reason, a different approach is taken to cool the rectifier unit in the proposed electric machine. It is arranged in a heat-transferring manner on the rotor body, which also contains the coolant channel. This means that the rectifier unit is located away from the coolant channel on the rotor body, so that it is ultimately thermally connected to the coolant channel via the rotor body. Therefore, it is neither intended to place the rectifier unit within the coolant channel nor to simply attach it to the rotor body.

[0013] Rather, it is located outside the coolant channel but is thermally connected to the rotor body, so that heat generated by it is dissipated via the rotor body towards the coolant channel and ultimately to the coolant. A poorly conductive or electrically insulating oil, such as thermal oil, is used as the coolant. The rotor body is made of a thermally conductive material, particularly metal. Preferably, the rotor body is made of steel, aluminum, or copper, or at least incorporates these materials. This enables extremely efficient cooling of the rectifier assembly using the coolant.

[0014] The thermal connection of the rectifier assembly to the rotor body is achieved, for example, by a surface-mounted contact of the rectifier assembly with the rotor body or by means of an additional heat-conducting element arranged between the rectifier assembly and the rotor body. Due to the improved cooling of the rectifier assembly compared to conventional electric machines, the rated power of the electric machine can be significantly increased, or the rectifier assembly can be designed to be smaller.

[0015] The invention provides that the rectifier assembly comprises a printed circuit board (PCB) which is connected to the rotor body via a thermal interface material. The PCB forms the base of the rectifier assembly and carries one or more electrical components, for example, semiconductor components. The PCB is thermally connected to the rotor body via the thermal interface material. For this purpose, the thermal interface material rests against both the PCB and the rotor body, preferably over a surface area. Preferably, the area over which the thermal interface material rests against the PCB has a surface area similar to that over which the thermal interface material rests against the rotor body. For example, the surface areas differ by at most 20%, at most 10%, or at most 5%.

[0016] The heat-conducting element consists of a thermally conductive material, i.e., a material with high thermal conductivity. The heat-conducting element ensures good thermal contact between the circuit board and the rotor body, so that the heat generated on the circuit board is efficiently transferred to the rotor body and thus towards the coolant channel.

[0017] A further development of the invention provides that the thermal conductivity element is a thermal paste, a thermal pad, a thermally conductive adhesive, a phase change element, or solder from a soldered joint. These elements are highly suitable for the thermal connection of the rectifier assembly to the rotor body. In the case of the phase change element, which serves as a latent heat storage medium, intermediate storage of the heat generated at the rectifier assembly is also achieved. The rectifier assembly is thus initially cooled, at least partially, by the phase change element itself; only after a time delay is the heat transferred from the rectifier assembly via the phase change element to the rotor body and consequently to the coolant.

[0018] It may also be provided that the rectifier assembly is materially bonded to the rotor body, in particular by soldering or welding. This is especially the case if the rectifier assembly is designed as a metal-core circuit board. In this case, a particularly effective heat transfer between the rectifier assembly and the rotor body can be achieved by means of the soldered connection. In any case, the aforementioned elements ensure reliable cooling of the rectifier assembly.

[0019] A further development of the invention provides that the printed circuit board is a metal-core printed circuit board and has at least one layer made of metal, preferably aluminum or copper, as well as a conductor arrangement with at least one conductor that is arranged on the printed circuit board layer via an insulating layer. The design of the printed circuit board as a metal-core printed circuit board has the advantage that the heat is distributed evenly within the printed circuit board, thus achieving a uniform temperature distribution across the rectifier device.

[0020] The metal core circuit board comprises a metal circuit board layer and a conductor arrangement. The conductor arrangement includes at least one conductor that is electrically connected to at least one component of the rectifier assembly. The conductor arrangement, or rather its conductor, thus provides electrical contact to the electrical component(s) of the rectifier assembly.

[0021] The conductor track arrangement, its conductor track, and the at least one electrical component of the rectifier assembly are electrically separated from the printed circuit board layer by means of an insulating layer. This insulating layer is a dielectric layer and prevents electrical contact between the aforementioned elements and the metal printed circuit board layer. The printed circuit board layer consists of a thermally conductive metal, preferably aluminum or copper. The metal-core printed circuit board can also be referred to as an IMS printed circuit board (IMS: Insulated Metallic Substrate). The use of a metal-core printed circuit board offers the advantage of uniform heat distribution within the board and effective heat dissipation towards the rotor body.

[0022] The invention provides that the rectifier device is arranged on a rotor wall of the rotor body, and the rotor winding is arranged on a side of the rotor wall facing away from the rectifier device. The rotor wall thus separates the rectifier device from the rotor winding, particularly in the axial direction. For example, the rectifier device rests against the rotor wall on one side, and the rotor winding rests against the rotor wall on the other. The rotor wall can also be referred to as a rotor balancing disk. It is an integral part of the rotor body, which is preferably designed as a single piece to achieve good thermal conductivity.

[0023] The arrangement of the rectifier unit on the rotor wall has the advantage that it is already designed and configured to dissipate heat from the rotor winding towards the coolant channel and the coolant contained therein. The heat generated by the rectifier unit can thus be dissipated together with the heat from the rotor winding. Furthermore, by arranging the rectifier unit on the rotor body, particularly on the rotor wall, a comparatively large installation space is available, allowing the rectifier unit to be designed for high electrical power outputs. This makes the realization of a high-power electric machine readily possible.

[0024] The invention provides that a projection extends from the rotor wall, on which a secondary winding of the rotor is arranged, cooperating with a primary winding of the stator for inductive energy transfer, and the rectifier device is electrically connected to the secondary winding. The primary winding and the secondary winding form an energy transfer device for transferring electrical energy from the stator to the rotor or vice versa. The primary winding is fixedly connected to the stator and the secondary winding is fixedly connected to the rotor, so that the secondary winding, together with the rotor, is rotatably mounted about the axis of rotation relative to the primary winding and the stator.

[0025] The rectifier is electrically connected to the secondary winding. This means that it is connected to the AC power source via the power transmission device, i.e., the secondary and primary windings. An inverter, for example, serves as the AC power source, converting direct current (DC) supplied by a DC power source into alternating current (AC).

[0026] The secondary winding is arranged on the projection extending from the rotor wall. Preferably, the projection extends axially from the rotor wall, thus projecting beyond it in the axial direction. Preferably, the projection and the rotor wall are formed as a single piece and made of the same material. In any case, they together form the rotor body, in which the coolant channel is located. Preferably, the coolant channel is located in both the rotor wall and the projection, so that both the rectifier and the power transmission components can be cooled by the coolant. The advantages already explained are achieved with the described design of the electric machine.

[0027] A further development of the invention provides that the rectifier device comprises at least one active semiconductor component. The active semiconductor component is an active electronic component designed as a semiconductor. For example, the active semiconductor component is in the form of an electronic switch, in particular a transistor, preferably a field-effect transistor, and most preferably a metal-oxide-semiconductor field-effect transistor. For example, the rectifier device comprises several such active semiconductor components, which together form a rectifier, for example a bridge rectifier or a center-tap rectifier.The use of the active semiconductor component has the advantage that electric current can be guided not only from the direction of the AC power source towards the rotor winding, but also in the reverse direction, i.e., from the direction of the rotor winding towards the AC power source. This enables an extremely rapid decay of the rotor magnetic field. Furthermore, the efficiency of the rectifier can be significantly increased.

[0028] The invention provides that a principal extension plane of the printed circuit board is angled relative to the axis of rotation. The principal extension plane of the printed circuit board is understood to be an imaginary plane extending in two directions perpendicular to each other, and in which the printed circuit board has its largest dimensions. The principal extension plane thus takes the form of a longitudinal median plane of the printed circuit board, which runs centrally within it with respect to the thickness of the printed circuit board.

[0029] The main extension plane is angled relative to the axis of rotation, thus forming an angle with it that is greater than 0° and less than 180°. Preferably, the angle is at least 45° and at most 135°, at least 60° and at most 120°, at least 75° and at most 105°, or approximately or exactly 90°. Particularly when the main extension plane is arranged perpendicular to the axis of rotation, a particularly advantageous thermal connection of the rectifier assembly to the rotor body, more precisely to the rotor wall, can be achieved, resulting in efficient use of installation space.

[0030] The invention further relates to a method for operating an electric machine, in particular an electric machine as described herein, wherein the electric machine has a stator and a rotor rotatably mounted about an axis of rotation relative to the stator, the rotor having a coolant channel through which coolant flows at least temporarily, and a rotor winding for generating a rotor magnetic field, which is connected to an alternating current source via a rectifier device arranged on the rotor. It is provided that the rectifier device is arranged in a heat-transferring manner on a rotor body of the rotor which accommodates the coolant channel, so that the rectifier device is thermally connected to the coolant channel via the rotor body and is cooled at least temporarily by means of the coolant.It is further provided that the rectifier device has a printed circuit board which rests against the rotor body via a heat conducting element, wherein the rectifier device is arranged on a rotor wall of the rotor body and the rotor winding is arranged on a side of the rotor wall facing away from the rectifier device, wherein a projection extends from the rotor wall on which a secondary winding of the rotor, cooperating with a primary winding of the stator for inductive energy transfer, is arranged, and the rectifier device is electrically connected to the secondary winding, wherein a main extension plane of the printed circuit board is angled relative to the axis of rotation.

[0031] The advantages of such a procedure or such a design of the electric machine have already been mentioned. Both the electric machine and the method for operating it can be further developed as described in this document, and reference is made to that description in that regard.

[0032] A further development of the invention provides that, by means of the rectifier device, electric current is transferred intermittently from the AC power source to the rotor winding and intermittently from the rotor winding to the AC power source. The transfer of electric current from the AC power source to the rotor winding builds up the rotor magnetic field, and the transfer from the rotor winding to the AC power source reduces it. This allows for particularly rapid adjustment of the rotor magnetic field, so that a specific operating point of the electric machine is reached more quickly than with known electric machines.

[0033] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, are also to be considered as encompassed by the invention.

[0034] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The only embodiment shown is... Fig. 1 A schematic longitudinal section view through a section of an electric machine.

[0035] The Fig. Figure 1 shows a schematic longitudinal section of an electric machine 1, which has a stator 2 and a rotor 3. The rotor 3 is rotatably mounted relative to the stator 2 about an axis of rotation 4. The electric machine 1 has a power transmission device 5 with a primary winding 6 and a secondary winding 7, wherein the primary winding 6 is fixedly connected to the stator 2 and the secondary winding 7 is fixedly connected to the rotor 3. An alternating current source (not shown) is electrically connected to a rotor winding 8 of the rotor 3 via the power transmission device 5, namely via a rectifier device 9.

[0036] The rectifier unit 9 serves to convert the alternating current supplied by the AC power source into a direct current, with which the rotor winding 8 is supplied, at least temporarily. The rectifier unit 9 has a printed circuit board 10, which is preferably designed as a metal-core printed circuit board. One or more electrical components 11 are arranged on the printed circuit board 10, which are only indicated and labeled here by way of example. The components 11 are preferably active semiconductor components and serve to rectify the alternating current from the AC power source into the direct current for the rotor winding 8.

[0037] The heat generated in the rectifier unit 9 is dissipated via the rotor 3 of the electric machine, more precisely via a rotor body 12 of the electric machine. For this purpose, the circuit board 10 is connected to the rotor body 12 via a heat-conducting element 13. The heat-conducting element 13 is, for example, a thermal paste, thermal pad, or the like. It can be seen that the rectifier unit 9 is arranged on a rotor wall 14, on which the rotor winding 8 is also located. In particular, the rotor wall 14 is arranged between the rectifier unit 9 and the rotor winding 8; the aforementioned elements are therefore located on opposite sides of the rotor wall 14.

[0038] A projection 15 extends axially from the rotor wall 14 with respect to the axis of rotation 4. The power transmission device 5, in particular the secondary winding 7, is arranged on this projection. The rectifier device 9 and the power transmission device 5 are thus axially offset, and in particular spaced apart from each other. A coolant channel 16 is provided in the rotor 3, through which coolant flows at least temporarily, as indicated by arrows 17. This serves, firstly, to cool the rotor winding 8, and secondly, to dissipate the heat generated in the rectifier device 9 towards the coolant channel 16 and thus into the coolant. This is indicated by arrows 18, which are only partially labeled.

[0039] The described electric machine 1 is characterized by excellent thermal integration of the rectifier unit 9 with the rotor 3. This makes it possible to increase the rated power of the electric machine 1 and to dispense with a redundant design of the rectifier unit 9. In particular, the described arrangement of the rectifier unit 9 on the rotor wall 14 allows for optimal use of the available installation space. This enables a further increase in the rated power of the electric machine 1. REFERENCE MARK LIST: 1 electric machine 2 Stator 3 Rotor 4 axis of rotation 5 Energy transmission device 6 Primary winding 7 Secondary winding 8 Rotor winding 9 Rectifier unit 10 circuit boards 11 Component 12 rotor bodies 13 Heat conducting element 14 Rotor wall 15 lead 16 Coolant channel 17 Arrow 18 Arrow

Claims

[1] Electric machine (1) with a stator (2) and a rotor (3) rotatably mounted about an axis of rotation (4) with respect to the stator (2), wherein the rotor (3) has a coolant channel (16) for flow with a coolant and a rotor winding (8) for generating a rotor magnetic field, which is connected to an alternating current source via a rectifier device (9) arranged on the rotor (3), wherein the rectifier device (9) is arranged in a heat-transferring manner on a rotor body (12) of the rotor (3) which receives the coolant channel (16), so that the rectifier device (9) is thermally connected to the coolant channel (16) via the rotor body (12), characterized by, that the rectifier device (9) has a printed circuit board (10) which is in contact with the rotor body (12) via a heat conducting element (13), wherein the rectifier device (9) is arranged on a rotor wall (14) of the rotor body (12) and the rotor winding (8) is arranged on a side of the rotor wall (14) facing away from the rectifier device (9), wherein a projection (15) extends from the rotor wall (14) on which a secondary winding (7) of the rotor (3) is arranged which interacts with a primary winding (6) of the stator (2) for inductive energy transfer, and the rectifier device (9) is electrically connected to the secondary winding (7), wherein a main extension plane of the printed circuit board (10) is angled relative to the axis of rotation (4). [2] Electric machine according to claim 1, characterized by , that the thermal conducting element (13) is a thermal paste, a thermal pad, a thermal adhesive, a phase change element or solder of a solder joint. [3] Electric machine according to any one of the preceding claims, characterized by , that the printed circuit board (10) is a metal core printed circuit board and has at least one printed circuit board layer made of metal and a conductor arrangement with at least one conductor which is arranged on the printed circuit board layer via an insulating layer. [4] Electric machine according to any one of the preceding claims, characterized by that the rectifier device (9) has at least one active semiconductor component (11). [5] Method for operating an electric machine (1), in particular an electric machine (1) according to one or more of the preceding claims, wherein the electric machine (1) has a stator (2) and a rotor (3) rotatably mounted about an axis of rotation (4) with respect to the stator (2), wherein the rotor (3) has a coolant channel (16) through which coolant flows at least temporarily and a rotor winding (8) for generating a rotor magnetic field, which is connected to an alternating current source via a rectifier device (9) arranged on the rotor (3), wherein the rectifier device (8) is arranged in a heat-transferring manner on a rotor body (12) of the rotor (3) which receives the coolant channel (16), so that the rectifier device (9) is thermally connected to the coolant channel (16) via the rotor body (12) and is cooled at least temporarily by means of the coolant, characterized by, that the rectifier device (9) has a printed circuit board (10) which is in contact with the rotor body (12) via a heat conducting element (13), wherein the rectifier device (9) is arranged on a rotor wall (14) of the rotor body (12) and the rotor winding (8) is arranged on a side of the rotor wall (14) facing away from the rectifier device (9), wherein a projection (15) extends from the rotor wall (14) on which a secondary winding (7) of the rotor (3) is arranged which interacts with a primary winding (6) of the stator (2) for inductive energy transfer, and the rectifier device (9) is electrically connected to the secondary winding (7), wherein a main extension plane of the printed circuit board (10) is angled relative to the axis of rotation (4). [6] Method according to claim 5, characterized by, that by means of the rectifier device (9) electric current is transferred temporarily from the AC source to the rotor winding (8) and temporarily from the rotor winding (8) to the AC source.

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