Method for de-exciting rotor of electric machine, control device, electric machine and motor vehicle

Abstract

The invention relates to a method for de-exciting a rotor winding of a rotor of an electric machine (2) of a motor vehicle (1), the electric machine comprising a stator and a rotor mounted rotatably relative to the stator, the rotor having a rotor winding for generating a rotor magnetic field, an active rectifier being arranged on the rotor side, the rectifier comprises at least one field effect transistor which can be actuated by means of an actuation voltage, the rectifier electrically connects a voltage source present on the rotor side to the rotor winding, by means of which an alternating voltage provided by the voltage source can be converted into a direct voltage, the field effect transistor or at least one of the field effect transistors is brought into an operating state, in which the respective field effect transistor forms an ohmic resistance, by means of a control voltage, and the energy stored in the rotor winding causes a current to flow through the at least one field effect transistor forming the ohmic resistance, at least a portion of the energy is converted into thermal energy.

Description

Technical Field

[0001] The present invention relates to a method for demagnetizing the rotor winding of a motor for a motor vehicle, wherein the motor includes a stator and a rotor supported in a manner rotatable relative to the stator, the rotor having rotor windings for generating a rotor magnetic field. Background Technology

[0002] Electric motors are commonly used as traction motors in motor vehicles, which can be pure electric vehicles or hybrid vehicles. An electric motor consists of a stator and a rotor supported in a manner rotatable relative to the stator. Windings composed of conductor wires are arranged on both the stator and rotor sides, and permanent magnets are provided where necessary. The electromagnetic interaction between the magnetic fields generated by the windings and the possible permanent magnets results in driving or braking torque. If there are no windings on the rotor side and only permanent magnets are present, it is also called a permanent magnet synchronous motor. If there are no permanent magnets on the rotor side and only windings (also called rotor windings) are present, it is called a separately excited synchronous motor. In separately excited synchronous motors, additional degrees of freedom exist in the control and design process.

[0003] A problem associated with separately excited synchronous motors is the induction of high currents or high voltages under certain conditions or in fault conditions, especially when a strong magnetic field is generated by the rotor windings. This can damage electrical components or semiconductor parts. As a countermeasure, the rotor windings are de-excited, that is, the magnetic field present on the rotor winding side, i.e., the energy stored in the rotor windings, is eliminated selectively and as quickly as possible. For this purpose, it is generally stipulated that the energy stored at the rotor winding ends be dissipated, i.e., converted into heat energy, in particular. Corresponding ideas are known, for example, from DE 10 2009 040 394 A1, DE 10 2022 121 516 A1, and US2013 / 0 193 903A1. Summary of the Invention

[0004] The object of this invention is to provide an advantageous solution for demagnetizing the rotor windings of an electric motor, particularly an advantageous solution in terms of its simplicity and low cost of implementation.

[0005] According to the present invention, in a method of the type described at the beginning, this objective is achieved by providing an active rectifier on the rotor side, the active rectifier comprising at least one field-effect transistor that can be driven by a drive control voltage, wherein the rectifier electrically connects a voltage source present on the rotor side to the rotor winding, and the AC voltage provided by the voltage source can be converted into a DC voltage by means of the rectifier, wherein, in order to demagnetize the rotor winding, the field-effect transistor or at least one of the field-effect transistors is brought into an operating state by means of the drive control voltage, in which the corresponding field-effect transistor forms an ohmic resistor, wherein the energy stored in the rotor winding causes a current to flow through at least one field-effect transistor forming an ohmic resistor, thereby converting at least a portion of this energy into heat energy.

[0006] This invention is particularly based on the concept that, in addition to its original function of rectifying voltage, the rectifier is given an additional function: in the event of deexcitation of the rotor windings, especially rapid deexcitation, the rectifier functions as a device for converting the energy stored in the rotor windings. Deexcitation is understood as the process of extracting energy present on the rotor winding side from the rotor windings during deexcitation; this energy exists or is stored within the electromagnetic field generated on the rotor winding side. In this invention, this energy is dissipated, i.e., converted into heat. Since a normally existing component, namely the rectifier, is used for this purpose, no additional components specifically designed for it are required, which helps to simplify the structure, minimize manufacturing effort, and reduce the overall weight of the motor as much as possible.

[0007] The rotor is supported in a rotatable manner relative to the stator, which typically has stator windings for generating a stator magnetic field. For this purpose, the rotor shaft can be supported by appropriate bearings, such as ball bearings or roller bearings. Preferably, the rotor and stator are arranged within the motor housing, wherein the stator is preferably arranged to be fixed in position relative to the housing. In the assembled state, the housing is fixedly connected to the vehicle body.

[0008] The rotor winding and / or stator winding has at least one conductive wire, which is wound, for example, around the rotor teeth or stator teeth. The windings serve as excitation coils, which generate a magnetic field, i.e., a rotor magnetic field or a stator magnetic field, when energized.

[0009] A rectifier is understood, in particular, as an electrical component comprising at least one field-effect transistor, typically multiple field-effect transistors. Therefore, a rectifier, or at least the at least one field-effect transistor, can be manipulated by means of a control signal, which may be intended to control the operation of the rectifier, for example, to perform rectification and, if necessary, inversion. Compared to active rectifiers, passive rectifiers typically only have semiconductor diodes, so that the AC voltage applied at the input of the rectifier is always converted into a DC voltage appearing at the output of the rectifier, regardless of the control signal. However, according to the present invention, an active rectifier is provided.

[0010] For a field-effect transistor (also referred to as a FET transistor), it is conceivable that the FET, or at least one of the FETs, is a metal-oxide-semiconductor field-effect transistor. In this case, the FET can also be referred to as a MOSFET transistor. It is conceivable that a control signal is applied to the corresponding FET as a gate-source voltage, wherein the current associated with the source-drain voltage is controlled according to the gate-source voltage. If the FET implements an ohmic resistance, the source-drain voltage is accompanied by a power loss, which causes the dissipation of electrical energy stored in the rotor winding. The corresponding operating state of the FET can also be referred to as the linear operating state. In this state, the FET has a constant resistance and behaves as a voltage-controlled resistance whose value is determined by the gate-source voltage.

[0011] For metal-oxide-semiconductor (MOSFETs), various operating states can be selectively triggered based on control signals or gate-source voltages. Specifically, when the gate-source voltage reaches a corresponding value, the MOSFET acts as a switch for the source-drain current, and these operating states are selectively set during rectification using control signals. Another operating state (whose occurrence depends on the gate-source voltage value) is also known as the linear operating state, in which the MOSFET acts as an ohmic resistor. The linear operating state occurs when the gate-source voltage is greater than a threshold voltage, defined as the voltage value at which the source-drain current first flows. Furthermore, the linear operating state may also occur when the source-drain voltage is less than the gate-source voltage. This linear operating state is generally avoided during normal motor operation because it carries the risk of MOSFET burnout. However, within the scope of this invention, control signals are generated in a targeted manner so that the metal oxide semiconductor field-effect transistor is in this working state during the demagnetization of the stator winding, wherein the electrical characteristics of the metal oxide semiconductor field-effect transistor at this time are used in a targeted manner to dissipate the energy present on the rotor winding side.

[0012] For the rectifier, it is preferably specified that the rectifier includes a circuit board and at least one field-effect transistor disposed on the circuit board, the circuit board having at least one, in particular, conductive conductor circuit. The circuit board is understood as a printed circuit board on which semiconductor structural elements are disposed. The circuit board may be made of plastic. The semiconductor structural elements may be fastened to the circuit board by means of soldering and / or press-fit connections. Preferably, the circuit board has a planar, in particular, flat extension, which may be parallel to the outer surface of the cooling section carrying the circuit board in order to achieve the most efficient thermal connection possible.

[0013] It is conceivable that, in order to demagnetize the rotor winding, a drive control voltage is used to bring at least one of the field-effect transistors (FETs) into an operating state in which the corresponding FET forms an ohmic resistor with a preset resistance value. Within the scope of this embodiment, the drive control voltage is not simply generated to make the FET operate at any position in the linear operating state. Instead, targeted drive control is performed so that the FET has a specifically preset resistance value. This resistance value can be selected such that, on the one hand, the energy stored in the rotor winding is dissipated sufficiently and effectively, but on the other hand, the FET does not overheat, causing damage or burnout.

[0014] Particularly preferably, when the corresponding field-effect transistor (FET) is put into an operating state in which the FET forms an ohmic resistance with a preset resistance value, the temperature dependence of the resistance value is considered. That is, in the linear operating state, the resistance value achieved by means of the FET is related not only to the gate-source voltage but also to the current temperature of the FET. Therefore, temperature dependence is another control basis for generating the drive voltage. Consequently, within the linear operating range, the MOSFET exhibits a decrease in ohmic resistance with increasing temperature when the gate-source voltage remains constant, which may lead to FET burnout.

[0015] Specifically, temperature dependence can be considered when determining the current temperature of the corresponding field-effect transistor. Therefore, within the scope of this embodiment, the specific result of determining the temperature of the field-effect transistor constitutes the control basis, thereby allowing the actual temperature of the field-effect transistor to be included in the corresponding control as realistically as possible. Within the scope of this embodiment, burnout can be avoided by reducing the gate-source voltage to offset or compensate for the decrease in resistance caused by temperature when the field-effect transistor heats up.

[0016] The current temperature can be determined using measurement techniques. Therefore, a temperature sensor can be placed within the region of the rectifier or field-effect transistor, by which a measurement value related to the temperature present at the current location can be generated. Alternatively, the current temperature can be determined based on a model and / or a lookup table. This implementation saves hardware components compared to detecting temperature using measurement techniques. Using a model, the correlation of the physical or electrical parameters of the field-effect transistor can be determined based on the specific structural design of the transistor. The results can also be stored and used as a lookup table.

[0017] During the demagnetization of the rotor windings using a field-effect transistor (FET), the FET may generate excessive heat in its region, which may require targeted heat dissipation. To address this issue, it is conceivable that the FET, or at least one of the FETs, is arranged on or in the cooling section of the rotor forming a heat sink / heat dissipation structure. According to this embodiment, thermal coupling between the heat sink and the FET causes or enhances the heat dissipation of the FET. For this purpose, the FET is preferably in direct contact with the heat sink, preferably in contact with the heat sink except for a thermally conductive medium provided, if necessary, to secure the FET.

[0018] Particularly preferably, within the scope of conceivable improvements, the cooling section has at least one cooling channel through which cooling fluid can flow. The cooling channel is understood as a rotor cavity or chamber configured to guide the cooling fluid. Preferably, the cooling channel is designed to be elongated, wherein the cooling fluid flows longitudinally through the cooling channel. In particular, the rotor, made of metal, has an outer surface on which field-effect transistors can be positioned. Preferably, the cooling channel extends directly below the outer surface region where the rectifier or field-effect transistor is arranged. Preferably, the cooling fluid is a coolant, such as water or oil.

[0019] Particularly preferably, in the cooling channel, or in at least one of the cooling channels, at least one channel wall defining the cooling channel is provided, the channel wall having a deflection structure that deflects the fluid flowing along the channel wall, particularly forming vortices. Therefore, the deflection structure can be any geometry of the channel wall surface, different from a smooth or flat structure. The deflection structure may have an arched portion protruding or bulging from the channel wall and arranged in the cooling channel on its inner side. The deflection structure may be provided, particularly only, in the cooling channel section located directly below the rectifier. The deflection structure transforms the laminar flow of the cooling fluid that may exist in the cooling channel into turbulent flow, thereby making the transfer of heat to the cooling fluid more efficient. The deflection structure may have at least one cooling fin and / or at least one cooling rib. The cooling fin or cooling rib is particularly understood as a bridge-shaped elongated structure extending longitudinally along the channel wall. The longitudinal direction can be arranged perpendicular or inclined relative to the flow direction of the cooling fluid, thereby correspondingly enhancing the deflection effect on the cooling fluid. The deflection structure may have multiple cooling fins or cooling ribs arranged sequentially along the flow direction.

[0020] The rectifier, or one of its circuit boards, can be fastened to the cooling section. A thermally conductive medium can be disposed between the circuit board and the cooling section. The thermally conductive medium is understood to be a material with a sufficiently high thermal conductivity to facilitate heat transfer from the rectifier to the cooling section as efficiently as possible. The thermal conductivity can have a value of at least 10 W / (m K). Preferably, the thermally conductive medium is a thermally conductive adhesive, and thus, in addition to achieving the most efficient heat transfer possible, the thermally conductive medium also serves as a fastener used to secure the rectifier to the cooling section.

[0021] Alternatively, the circuit board may have a metal core. Since metals generally have high thermal conductivity, heat transfer through the circuit board is more efficient as part of the heat transfer from at least one field-effect transistor to the cooling fluid. This is advantageous, for example, when the carrier structure of the circuit board, apart from the metal core and any conductor circuitry present, is made of plastic. The metal core can be made of aluminum and / or copper. The metal core is covered, particularly in the direction toward the field-effect transistor, by a layer of plastic. In principle, the same applies to the direction toward the cooling section, where the metal core can also be exposed, allowing for direct contact between the metal core and the cooling section, in addition to any possible thermally conductive medium.

[0022] Preferably, the motor has an induction rotary transformer, which includes at least one rotor-side excitation coil present on the rotor side and forming a voltage source, and at least one stator-side excitation coil present on the stator side, wherein electrical energy can be transferred from the stator-side excitation coil to the rotor-side excitation coil in an inductive manner. The induction rotary transformer enables contactless and therefore low-wear or wear-free power transfer from the stator to the rotor. The rotor-side and stator-side excitation coils move past each other during rotor rotation, wherein the magnetic field generated on the stator-side excitation coil side induces a voltage on the rotor-side excitation coil side by means of electromagnetic induction. Therefore, the rotor-side excitation coil serves as a voltage source, wherein the generated voltage is in the form of an alternating current (AC) voltage. This AC voltage is converted to a DC voltage required for operating or energizing the stator windings by means of a rectifier. Preferably, a plurality of excitation coils are arranged concentrically about the rotor's axis of rotation and thus circumferentially.

[0023] Although the present invention specifies demagnetizing the rotor windings using a field-effect transistor that realizes ohmic resistance, alternative methods are conceivable as possible alternatives, especially when determining the operating state of the motor or vehicle. Therefore, as an alternative to demagnetizing the rotor windings using a rectifier, the DC voltage present on the rotor winding side can be converted to an AC voltage, wherein energy stored in the rotor windings is transferred from the rotor-side excitation coil to the stator-side excitation coil in an inductive manner. For this purpose, the rectifier is brought into a state by means of a correspondingly generated drive voltage, in which the DC voltage present on the rotor winding side is converted to an AC voltage, which is then applied to the rotor-side excitation coil. Accordingly, power is directed to the stator-side excitation coil. Thus, within the scope of this embodiment, bidirectional power or energy transfer is achieved by means of a rotary transformer and a rectifier.

[0024] It is conceivable that a check is made to determine if a dissipation condition is met, which is only met or can be met under the condition that at least one safety message exists indicating that the motor and / or vehicle is in an operating state where energy transfer from the rotor-side excitation coil to the stator-side excitation coil is unfavorable. If the dissipation condition is not met, demagnetization of the rotor windings can be achieved by transferring energy stored in the rotor windings from the rotor-side excitation coils to the stator-side excitation coils. If the dissipation condition is met, demagnetization of the rotor windings can be achieved by converting the energy stored in the rotor windings into heat energy through at least one field-effect transistor forming an ohmic resistance. The presence of a safety message can mean that components of the motor and / or vehicle may be damaged in the event of energy transfer from the rotor-side excitation coils to the stator-side excitation coils. The safety message can also indicate that such transfer could pose a hazard to the user, for example, due to the exposure of live parts, which is particularly likely in the event of an accident.

[0025] The safety information, or at least one of the safety information, may indicate that the state of charge (SOC) of the vehicle's electric accumulator (which provides electrical energy for operating the motor) and, if necessary, the SOC of the motor's intermediate circuit capacitors, exceeds a preset threshold. That is, the energy transferred from the rotor-side excitation coil to the stator-side excitation coil is typically used to charge the electric accumulator, but this is not possible when the accumulator has a correspondingly high SOC. The preset threshold can be chosen such that it is exceeded once the accumulator is fully charged or no longer has sufficient additional free storage capacity to absorb the transferred energy. The corresponding safety information can be obtained based on information related to the current SOC of the electric accumulator present during vehicle control. Alternatively, it is conceivable that the SOC is detected by measurement techniques. It is also conceivable that the safety information, or at least one of the safety information, indicates a fault condition on the drive unit side of the vehicle. This particularly relates to the already mentioned scenario where an accident occurs in the vehicle. In this case, if a control signal, for example, triggers the vehicle's airbags, is present, safety information can be generated.

[0026] Furthermore, the present invention relates to a control device, particularly a control device for motor vehicles or electric motors. According to the invention, this objective is achieved in such a control device by having a computer-readable storage medium storing executable instructions, which, when executed by a processing unit of the control device, cause the processing unit to perform at least one of the steps of the method described above. Therefore, the control device is particularly adapted to generate and output a control signal for performing the method. The control signal can be directly a drive voltage output to at least one field-effect transistor. Alternatively, the drive voltage output to the field-effect transistor can be generated based on the control signal. Furthermore, the control device is preferably adapted to process related information, and in particular to check whether dissipation conditions are met. Furthermore, the control device is preferably adapted to generate and output control commands or drive voltages provided during rectification by means of a rectifier. All advantages, features, and aspects explained in conjunction with the method according to the invention can be similarly transferred to the control device according to the invention, and vice versa.

[0027] In particular, the control device is located at a different position than the rotor. Therefore, the controllable device can be located on the stator side or the motor side. Accordingly, it is necessary to transmit control commands or drive voltages from the fixed-position section, especially the stator, to the rotor. For this purpose, the motor can have an induction-type communication rotary transformer, which includes at least one rotor-side communication coil located on the rotor side and at least one stator-side communication coil located on the stator side, wherein control commands generated by the control device or drive voltages for controlling the rectifier's operation can be transmitted inductively from the stator-side communication coil to the rotor-side communication coil. The aspects explained above in conjunction with the induction-type rotary transformer are, in principle, equally and similarly applicable to the communication rotary transformer.

[0028] Furthermore, the present invention relates to an electric motor. In this motor, according to the invention, this objective is achieved by the following means: the motor includes: a control device, particularly the control device described above; a stator; and a rotor supported in a manner rotatable relative to the stator, the rotor having rotor windings for generating a rotor magnetic field, wherein an active rectifier is provided on the rotor side, the active rectifier including at least one field-effect transistor (FET) controllable by means of a drive voltage generated on the control device side, wherein the rectifier electrically connects a voltage source present on the rotor side to the rotor windings, and converts the AC voltage provided by the voltage source to a DC voltage by means of the rectifier, wherein, in order to demagnetize the rotor windings, the drive voltage can cause the FET or at least one of the FETs to enter an operating state in which the corresponding FET forms an ohmic resistance, wherein energy stored in the rotor windings causes a current to flow through at least one FET forming an ohmic resistance, thereby converting at least a portion of this energy into heat energy. All the advantages, features, and aspects explained in conjunction with the method and control device according to the invention can be similarly transferred to the electric motor according to the invention, and vice versa.

[0029] Preferably, the motor can be connected to the powertrain of a motor vehicle, wherein, in the connected state, the motor can generate traction torque, which can be transmitted to the wheels of the motor vehicle via the powertrain. Therefore, for example, an open rotor shaft end, particularly extending from the motor housing, can be provided, with the rotor shaft extending along the axis of rotation. This end and components of the powertrain can each have connectors, such as connecting flanges, by means of which a mechanical connection, particularly one that cannot be rotated relative to the shaft, can be established between the shaft and the powertrain. In principle, the powertrain includes all components that can be used to establish a mechanical connection between the motor and the wheels. Therefore, the powertrain can include a drive shaft and / or a transmission, particularly a shift transmission and / or a differential and / or a clutch.

[0030] Finally, the present invention relates to a motor vehicle, the motor vehicle comprising: a motor forming a traction motor, particularly a motor as described in the foregoing description paragraphs; and a control device, particularly a control device as described in the foregoing related description paragraphs, wherein the motor comprises a stator and a rotor supported in a manner rotatable relative to the stator, the rotor having rotor windings for generating a rotor magnetic field, wherein an active rectifier is provided on the rotor side, the active rectifier comprising at least one field-effect transistor that can be driven by a drive control voltage generated on the control device side, wherein the rectifier electrically connects a voltage source present on the rotor side to the rotor windings, and the rectifier converts an AC voltage provided by the voltage source into a DC voltage, wherein, in order to demagnetize the rotor windings, the drive control voltage can be used to bring the field-effect transistor or at least one of the field-effect transistors into an operating state in which the corresponding field-effect transistor forms an ohmic resistor, wherein energy stored in the rotor windings causes a current to flow through at least one field-effect transistor forming an ohmic resistor, thereby converting at least a portion of this energy into heat energy. All the advantages, features, and aspects of the method, control device, and motor according to the invention can be equally transferred to the motor vehicle according to the invention, and vice versa.

[0031] Preferably, the motor vehicle according to the invention includes an electric energy storage device in which energy usable for traction of the motor vehicle can be stored. This energy is in the form of electrical energy and is converted into kinetic energy by means of a motor. Conversely, it is conceivable that the motor operates in a recovery mode, in which the kinetic energy of the motor vehicle is converted into electrical energy stored in the energy storage device. The energy storage device (which can be, in particular, a lithium-ion battery) typically provides a DC voltage. However, the operation of the motor requires an AC voltage, so a power electronics unit can be provided at the motor terminals to convert the DC voltage provided at the energy storage device terminals into an AC voltage. The aforementioned or other control devices can be adapted to generate control signals intended to operate the power electronics unit and output them to the power electronics unit.

[0032] Preferably, the motor vehicle according to the invention includes a cooling system by means of which cooling fluid can be cooled, wherein the cooling section forming a heat sink / heat dissipation structure as explained above is integrated into the cooling system. Therefore, it can be specified that the cooling system forms a cooling cycle, in which cooling fluid can be conveyed by means of a conveying device. In this embodiment, the conveying device circulates the cooling fluid to the cooling section and then back again, thus performing a cycle. The conveying device may be a cooling fluid pump. A cooling device for cooling the cooling fluid, such as a heat exchanger, may be integrated into the cooling system. Attached Figure Description

[0033] Other advantages and details of the invention are illustrated in the following embodiments and given with reference to the accompanying drawings. Wherein, schematically:

[0034] Figure 1 A schematic diagram of a motor vehicle according to an embodiment of the invention, shown in a side view, is presented. The motor vehicle includes a motor according to an embodiment of the invention and a control device according to an embodiment of the invention.

[0035] Figure 2 It shows Figure 1 A schematic diagram illustrating the height of a motor in a motor vehicle.

[0036] Figure 3 A flowchart of a method according to the invention based on one embodiment is shown. Figure 1 The motor vehicles shown Figure 2 The motor shown illustrates this method.

[0037] Figure 4 It shows Figure 2 A partial schematic diagram showing the rectifier during rotor deexcitation of the motor, and...

[0038] Figure 5 The diagram illustrates the relationship between the values ​​of the drive control voltage and... Figure 2 A coordinate system relating the ohmic resistance values ​​of a motor's field-effect transistor at different temperatures during linear operation. Detailed Implementation

[0039] Figure 1 A motor vehicle 1 according to an embodiment of the invention is shown, which includes an electric motor 2 according to an embodiment of the invention. The electric motor 2 includes a rotor 3 and a stator 4. The electric motor 2 is an internal rotor and is designed as a separately excited synchronous motor. Therefore, the rotor 3 is arranged in a region further inward in the radial direction of the electric motor 2 than the region where the stator 4 is arranged. The rotor shaft 5 of the rotor 3 is rotatably supported on the housing 6 of the electric motor 2, for example by means of ball bearings or roller bearings.

[0040] The motor 2 is configured to operate in drive mode, in which it converts electrical energy stored in the electric energy storage tank 7 of the vehicle 1 into kinetic energy of the vehicle 1. The resulting driving torque for propelling the vehicle 1 can be transmitted from the motor 2 to the powertrain 8 of the vehicle 1. The driving torque can only be transmitted to the rear wheels, but additionally or alternatively, it can also be transmitted to the front wheels. Furthermore, the motor 2 can operate in regeneration mode, in which it converts the kinetic energy of the vehicle 1 into electrical energy, which can be used, for example, to charge the electric energy storage tank 7.

[0041] The following defines the relevant spatial directions for motor 2. Specifically, rotor shaft 5 is supported in a manner that allows it to rotate about axis 9, which extends along the longitudinal direction 10 of motor 2. Radial direction 11 extends perpendicular to longitudinal direction 10. Circumferential direction 12 extends perpendicular to radial direction 11. In other words, the point of rotation about axis 9 moves along circumferential direction 12.

[0042] The following explains the details regarding motor 2. Figure 2 A schematic diagram of the height of motor 2 is shown, illustrating the distribution of motor 2 components on rotor 3 and stator 4. A power electronics unit 13 is thus provided on the stator 4 side, by means of which the DC voltage supplied at the energy storage terminal 7 is converted to AC voltage. For this purpose, a control device 14 according to one embodiment of the invention is provided, adapted to generate control signals or corresponding drive voltages for controlling the operation of the power electronics unit 13, and outputting them to the power electronics unit. Although the control device 14 is shown as a component of motor 2 in this example, it could also be located outside of motor 2, and thus be a component of motor vehicle 1. The AC voltage generated by the power electronics unit 13 allows control of the stator windings of stator 4 (not shown in detail in the figure) and the rotor windings 15 of rotor 3 (in... Figure 2 (Only one of them is schematically shown in the diagram) is energized. The stator winding and rotor winding 15, which are composed of conductor wires respectively, generate magnetic fields due to the energization, that is, generate rotor magnetic field and stator magnetic field. These two magnetic fields interact in the process of generating driving torque or recovery torque.

[0043] The following explains the details of the transfer of electrical energy or power from the energy storage unit 7 to the stator winding 15. First, the DC voltage supplied at the energy storage unit 7 is converted to AC voltage using the power electronics unit 13. This AC voltage is then transmitted to the stator-side excitation coil 16 located on the stator 4 side. Through this excitation coil, energy is inductively transferred to the rotor-side excitation coil 17 located on the rotor 3 side. Therefore, the excitation coils 16 and 17 form an inductive rotary transformer, enabling contactless energy transfer from the fixed section of the stator 4 or motor 2 to its rotor 3.

[0044] The rotor-side excitation coil 17 provides a voltage source on the rotor 3 side, where an AC voltage exists. This AC voltage is supplied to the rectifier 19 of the rotor 3, which converts the AC voltage to a DC voltage. Therefore, the rectifier 19 connects the rotor-side excitation coil 17 to the rotor winding 15, thereby supplying the voltage provided by the rotor-side excitation coil 17 and converted to DC voltage by means of the rectifier 19 to the rotor winding 15 to generate a rotor magnetic field. The active rectifier 19 includes multiple, i.e., eight, field-effect transistors 23, wherein, for clarity, in Figure 2Only one of them is provided with a corresponding reference numeral, and in this example, the field-effect transistor is a metal-oxide-semiconductor field-effect transistor. The rectification of the AC voltage provided by the rotor-side excitation coil 17 is performed according to the drive control voltage generated on the control device 14 side, which is applied to one of the field-effect transistors 23.

[0045] Therefore, in addition to generating the control signal set for the power electronics unit 13, the control device 14 is also adapted to generate the control signal or drive voltage mentioned above for controlling the operation of the active rectifier 19, and output it to the active rectifier via the inductive communication rotary transformer 20. The communication rotary transformer 20 includes a stator-side communication coil 21 located on the stator 4 side and a rotor-side communication coil 22 located on the rotor 3 side, wherein the control signal of the control device 14 for operating the active rectifier 19 is transmitted inductively from the stator-side communication coil 21 to the rotor-side communication coil 22, and then immediately to the field-effect transistor 23. The operating principle of the communication rotary transformer 20 is substantially the same as that of the rotary transformer 18.

[0046] The normal operation of rectifier 19 is described below. During normal operation, rectifier 19 converts the AC voltage present on the excitation winding 17 side of the rotor side into a DC voltage. Therefore, rectifier 19 in this example includes eight field-effect transistors 23. Figure 2 In the schematic diagram shown, these field-effect transistors are arranged in a four-row, two-column configuration. During normal operation in which the rotor winding 15 is energized, a drive voltage is generated such that the four field-effect transistors 23 shown in the second and third rows are continuously turned on, while the other four field-effect transistors 23 operate in clock mode.

[0047] The following is for reference. Figure 3 , Figure 3 A flowchart of a method according to the invention based on one embodiment is shown. Figure 1 Motor vehicles and Figure 2 The method is explained using motor 2. The method includes steps 24-27. The processing and evaluation steps performed during the execution of this method, as well as the generation of the drive control voltage, are all completed at the control device 14. For this purpose, the control device 14 includes a computer-readable storage medium 28 storing executable instructions 29, which, when executed by the processing device 30 of the control device 14, cause the processing device to perform the steps specified in the context of this method.

[0048] For the first step 24, the initial condition is assumed to be that the rotor winding 15 should be de-energized. In step 24, the dissipation condition is checked by means of the control device 14, and the satisfaction of the dissipation condition depends on the presence of safety information 31. Safety information 31 exists only under specific conditions.

[0049] For example, the condition for the existence of safety information 31 is that the state of charge (SOC) of the electric accumulator 7 and / or, if necessary, the SOC of an intermediate circuit sensor of the motor (not shown in detail) exceeds a preset threshold. The preset threshold is selected such that it is exceeded when the electric accumulator 7 is fully charged. The corresponding safety information 31 is determined based on information related to the current SOC of the electric accumulator 7 present during vehicle control, wherein, additionally or alternatively, it is conceivable that the SOC can be detected by measurement techniques. Furthermore, safety information 31 exists in the event of a fault in the drive unit of the vehicle 1, such as the power electronics unit 13. This could be in the event of an accident. In this case, for example, if a control signal is present to trigger, for example, the airbag of the vehicle 1, safety information 31 is generated.

[0050] If one or more safety messages 31 exist, the dissipation condition is met; otherwise, the method continues in the next step 25. If the dissipation condition is not met, the rotor winding 15 is de-energized as described below. In this regard, by means of the rectifier 19, not only can the AC power present on the rotor-side excitation coil 17 be converted to the DC voltage present on the rotor winding 15, but the reverse conversion is also possible, thus enabling bidirectional energy transfer by means of the rotary transformer 18. During de-energization in step 25, a drive voltage is generated by means of the control device 14 and output to the field-effect transistor 23, causing the DC voltage present on the rotor winding 15 to be converted to an AC voltage, which in turn induces energy transfer from the rotor-side excitation coil 17 to the stator-side excitation coil 16. At this time, refer to... Figure 2 This turns on the four field-effect transistors 23 shown in the first and fourth rows, while the other four field-effect transistors 23 are in clock operation mode.

[0051] The following explains the case where the dissipation condition is met during step 24, i.e., at least one piece of safety information 31 exists. In this case, the method continues in steps 26 and 27, wherein step 26 is executed periodically in parallel with step 27. That is, in step 26, temperature information 32 related to the current temperature of the field-effect transistor 23 is determined. For this purpose, a temperature sensor, not shown in detail in the figure, is provided in the region of the rectifier 19. During data integration, the temperature information 32 is determined according to a model and a lookup table, which are stored, for example, at the control device 14. With the aid of the model, the correlation of the physical or electrical parameters of the field-effect transistor 23 is determined according to the specific structural design of the field-effect transistor, wherein the results can also be used within the scope of the lookup table.

[0052] In step 27, a drive voltage is thus generated on the control device 14 side, causing the field-effect transistors 23 to enter a linear operating state, in which each of the field-effect transistors 23 forms an ohmic resistor 33. This state is based on... Figure 4 It was pointed out that Figure 4 A rectifier 19 is shown, in which the field-effect transistor 23 is represented as a voltage-controllable resistor. For clarity, in Figure 4 Only one of the resistors 33 shown is provided with a corresponding reference numeral. Here, the value of the corresponding resistor 33 is related to the corresponding drive control voltage. Resistors 33 are formed by field-effect transistors 23. Due to power loss in resistors 33, field-effect transistors 23 heat up, which ultimately leads to demagnetization of the rotor coil 15. The current flowing through the field-effect transistor 23 or resistor 33 at this time... Figure 4 The dotted line is used to indicate this.

[0053] This generates a drive voltage on the control device 14 side, causing the corresponding field-effect transistor 23 to form an ohmic resistor 33 with a specific preset resistance value. For this purpose, the previously mentioned temperature information 32 is considered. Therefore, Figure 5A coordinate system 34 is shown relating the resistance value of the ohmic resistor 33 (plotted along the vertical axis 35) in milliohms to the corresponding drive voltage value in volts, which in this example forms the gate-source voltage and is plotted along the horizontal axis 36. Several curves are shown, each corresponding to a temperature value present in the field-effect transistor 23. Specifically, the temperature is 150°C on the line containing an unfilled circle, 125°C on the line containing a filled circle, 100°C on the line containing a star symbol, 75°C on the line containing a square symbol, 50°C on the line containing a triangle symbol, and 25°C on the line containing a diamond symbol. It can be seen that, with the temperature remaining constant, the resistance value decreases as the drive voltage value increases. In linear operating conditions (which involve...), Figure 5 In the steep section on the left side of the curve shown, the resistance value is highly correlated with temperature when the gate-source voltage remains constant. Therefore, as the temperature increases, the resistance decreases, which in turn leads to a larger current flowing through the field-effect transistor 23, causing the temperature to rise further. Without countermeasures, this vicious cycle could end with the field-effect transistor 23 burning out and becoming damaged. To address this, temperature information 32 is continuously and cyclically acquired during step 26, wherein the drive voltage is correspondingly reduced when the temperature rises, thereby increasing the resistance value and reducing the current, and thus suppressing the temperature rise.

[0054] Heat is generated in the region of the rectifier 19 as the energy present on the rotor winding 15 side is dissipated through the ohmic resistor 33. This is also true in principle for the normal operation of the rectifier 19. This heat generation necessitates targeted cooling in the region of the rectifier 19, the details of which are described below. Therefore, the vehicle 1 includes a cooling system (not shown in detail in the figures) that forms a cooling loop in which a cooling fluid circulates. To cool the cooling fluid, the cooling system also includes a cooling device, specifically a heat exchanger.

[0055] The rectifier 19 is arranged on the cooling section 37 of the rotor 3, which forms a heat sink. The cooling section is integrated into the cooling system 23 and is traversed by cooling fluid. The cooling section 37... Figure 3 The cooling fluid is shown in dashed lines. It enters from the conveying device into the cooling channel of the cooling section 37 (not shown in detail), reaches the cooling device, and then returns to the conveying device. The cooling channel, extending through the cooling section 37, is arranged directly below the rectifier 19. To achieve the most efficient heat transfer possible from the rectifier 19 to the cooling fluid, the material (metal in this example) of the rotor 3, left between the cooling channel and the rectifier 19, is as thin as possible, preferably only a few millimeters.

[0056] In the cooling channel, a deflection structure is provided on the channel wall that defines the cooling channel. This deflection structure causes the cooling fluid flowing through the cooling channel to be deflected and form a vortex. This achieves more efficient heat transfer from the rectifier 19 to the cooling fluid. The deflection structure includes multiple slender, bridge-shaped structures arranged sequentially perpendicular to the flow direction. These structures can also be referred to as cooling fins or cooling ribs.

Claims

1. A method for de-excitation of a rotor winding (15) of a rotor (3) of an electric machine (2) of a motor vehicle (1), wherein, The electric machine (2) comprises a stator (4) and a rotor (3) which is supported in a rotatable manner relative to the stator (4) and has a rotor winding (15) for generating a rotor magnetic field, wherein a voltage source is present on the rotor (3) side, which voltage source comprises at least one field effect transistor (23) which can be actuated by means of an actuation voltage, wherein the voltage source present on the rotor (3) side is electrically connected to the rotor winding (15) by means of the rectifier (19) and an alternating voltage provided by the voltage source can be converted into a direct voltage by means of the rectifier (19), wherein, in order to de-energize the rotor winding (15), the field effect transistor (23) or at least one of the field effect transistors (23) is brought into a state of operation by means of the actuation voltage in which the respective field effect transistor (23) forms an ohmic resistance (33), wherein the energy stored in the rotor winding (15) causes a current to flow through the at least one field effect transistor (23) which forms an ohmic resistance (33), such that at least a portion of the energy is converted into heat energy.

2. The method of claim 1, wherein, The field effect transistor (23) or at least one of the field effect transistors (23) is a metal-oxide-semiconductor field effect transistor.

3. The method of claim 2, wherein, In order to de-energize the rotor winding (15), the field effect transistor (23) or at least one of the field effect transistors (23) is brought into a state of operation by means of the actuation voltage in which the respective field effect transistor (23) forms an ohmic resistance (33) having a predefined resistance value.

4. The method of claim 3, wherein, The temperature dependency is taken into account when bringing the respective field effect transistor (23) into the state of operation in which the field effect transistor (23) forms an ohmic resistance (33) having a predefined resistance value.

5. The method of claim 4, wherein, The temperature dependency is taken into account in the case of a determination of a current temperature of the respective field effect transistor (23), wherein the determination of the current temperature is carried out in particular by means of measurement technology and / or according to a model and / or according to a look-up table.

6. The method according to any of the preceding claims, characterized in that, The field effect transistor (23) or at least one of the field effect transistors (23) is arranged on or in a cooling section (37) of the rotor (3), which cooling section forms a heat sink.

7. The method of claim 6, wherein, The cooling section (37) has at least one cooling channel which can be traversed by a cooling fluid.

8. The method according to any of the preceding claims, characterized in that, The electric machine (2) has an inductive resolver (18) which comprises at least one rotor-side field winding (17) which is present on the rotor (3) side and forms a voltage source, and at least one stator-side field winding (16) which is present on the stator (4) side, wherein electrical energy is transferred from the stator-side field winding (16) to the rotor-side field winding (17) in an inductive manner.

9. The method of claim 8, wherein, As an alternative to de-energizing the rotor winding (15) by means of the rectifier (19), a direct voltage present on the rotor winding (15) side is converted into an alternating voltage, wherein the energy stored in the rotor winding (15) is transferred from the rotor-side field winding (17) to the stator-side field winding (16) in an inductive manner.

10. The method of claim 9, wherein, checking whether a dissipation condition is fulfilled, wherein the dissipation condition is fulfilled or can be fulfilled only if at least one piece of safety information (31) is present, which indicates an operating state of the electric machine (2) and / or of the motor vehicle (1) in which an energy transfer from the rotor-side field winding to the stator-side field winding is disadvantageous, wherein, in the case of a non-fulfillment of the dissipation condition, de-excitation of the rotor winding (15) is effected by means of an energy transfer from the rotor winding (15) stored in the rotor-side field winding to the stator-side field winding, and, in the case of a fulfillment of the dissipation condition, de-excitation of the rotor winding (15) is effected by means of a conversion of the energy stored in the rotor winding (15) into heat energy by means of the at least one field effect transistor (23) forming an ohmic resistance (33).

11. The method of claim 10, wherein, The safety information (31) or at least one piece of the safety information (31) indicates that the state of charge of an electric energy store (7) of the motor vehicle (1) exceeds a predefined threshold value, the electric energy store providing electric energy for operating the electric machine (2).

12. The method according to claim 10 or 11, characterized in that, The safety information (31) or at least one piece of the safety information (31) indicates that a fault state is present on the drive unit side of the motor vehicle (1).

13. Control device (14) having a computer-readable storage medium (28) on which executable instructions (29) are stored, which, in the case of an execution of the instructions by means of a processing device (30) of the control device (14), cause the processing device to carry out at least one of the steps of the method according to any one of the preceding claims.

14. An electric machine (2) comprising: Control device (14), in particular according to claim 13; Stator (4) and rotor (3) supported in a rotatable manner relative to the stator (4), the rotor having a rotor winding (15) for generating a rotor field, wherein a source-side rectifier (19) is provided on the rotor (3) side, the rectifier comprising at least one field effect transistor (23) which can be controlled by means of a control voltage which can be generated by means of the control device (14), wherein the rectifier (19) electrically connects a voltage source present on the rotor (3) side to the rotor winding (15), by means of which an alternating voltage provided by the voltage source can be converted into a direct voltage, wherein, for de-excitation of the rotor winding (15), the field effect transistor (23) or at least one of the field effect transistors (23) is brought into an operating state by means of the control voltage, in which operating state the respective field effect transistor (23) forms an ohmic resistance (33), wherein the energy stored in the rotor winding (15) causes a current flow through the at least one field effect transistor (23) forming an ohmic resistance (33), so that at least a portion of the energy is converted into heat energy.

15. A motor vehicle (1) comprising: Electric machine (2) forming a traction electric machine, in particular according to claim 14; and a control device (14), in particular according to claim 13, wherein the electric machine (2) comprises a stator (4) and a rotor (3) which is supported in a rotatable manner relative to the stator (4), the rotor having a rotor winding (15) for generating a rotor field, wherein a source-sided rectifier (19) is provided on the rotor (3) side, the rectifier comprising at least one field effect transistor (23) which can be controlled by means of a control voltage which can be generated on the control device (14) side, wherein the rectifier (19) electrically connects a voltage source present on the rotor (3) side to the rotor winding (15), by means of which an alternating voltage provided by the voltage source can be converted into a direct voltage, wherein, in order to de-excite the rotor winding (15), the field effect transistor (23) or at least one of the field effect transistors (23) is brought into an operating state by means of the control voltage, in which operating state the respective field effect transistor (23) forms an ohmic resistance (33), wherein the energy stored in the rotor winding (15) causes a current to flow through the at least one field effect transistor (23) which forms an ohmic resistance (33), such that at least a portion of the energy is converted into heat energy.

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