Method for operating electric machine, control device, inverter circuit, stator, electric machine and motor vehicle

Abstract

The invention relates to a method for operating an electric machine of a motor vehicle, comprising a stator and a rotor which is mounted so as to be rotatable relative to the stator and which has a rotor winding, an inverter circuit being provided on the stator side, by means of which a DC voltage of a voltage source is converted into an AC voltage and output to at least one stator-side transmission coil, the power is transmitted to the rotor by means of the stator-side transmission coil in order to energize the rotor winding, and wherein the inverter circuit comprises a full-bridge circuit, which is connected to a voltage source via a half-bridge circuit and to at least one stator-side transmission coil, a control signal for controlling the transistors of the half-bridge circuit and the full-bridge circuit is generated and output by means of a control device such that the inverter circuit operates in a full-bridge operating mode in which a direct-current voltage at the voltage source side is completely converted into an alternating-current voltage by means of the inverter circuit, or in a half-bridge operating mode in which the direct-current voltage at the voltage source side is completely converted into an alternating-current voltage by means of the inverter circuit. Only the DC voltage on the voltage source side is partially converted into the AC voltage by means of the inverter circuit.

Description

Technical Field

[0001] The present invention relates to a method for operating an electric motor for a motor vehicle, wherein the motor includes a stator and a rotor supported in a rotatable manner relative to the stator, the rotor having rotor windings for generating a rotor magnetic field, wherein an inverter circuit is provided on the stator side to convert a DC voltage from a voltage source into an AC voltage and output it to at least one stator-side transmission coil, wherein power is inductively transmitted to the rotor by means of the stator-side transmission coil to energize the rotor windings. 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] The energy stored in the electric accumulator of a motor vehicle is used to operate the motor. Specifically, the electric accumulator provides a DC voltage, which needs to be converted to an AC voltage on the stator side to transfer energy to the rotor via induction. For this purpose, on the stator side, a voltage source is connected to an inverter circuit, which is provided by or connected to the electric accumulator. The inverter circuit converts the DC voltage present on the voltage source side into an AC voltage. For example, corresponding solutions are known from DE102020119598A1, CN 114 285 285A, and CN 111 817 449A.

[0004] In particular, because the range of current DC voltage values ​​used at the voltage source is quite large, for example, between 350V and 920V, a common problem is that when the DC voltage value is high and the power value to be transferred from the stator to the rotor is low, the effectiveness or efficiency of inversion and power transfer is very low. This is disadvantageous. Summary of the Invention

[0005] The object of this invention is to provide an improvement in motors with inductive power transfer from the stator to the rotor, particularly an improvement in terms of maximizing efficiency.

[0006] According to the present invention, in the method of the type described at the beginning, this objective is achieved by the following means: the inverter circuit includes a full-bridge circuit, which is connected to a voltage source on one hand via a half-bridge circuit and to at least one stator-side transmission coil on the other hand. A control device generates and outputs control signals for controlling transistors in the half-bridge and full-bridge circuits, thereby enabling the inverter circuit to operate in either a full-bridge operating mode or a half-bridge operating mode. In the full-bridge operating mode, the inverter circuit completely converts the DC voltage present on the voltage source side into an AC voltage. In the half-bridge operating mode, the inverter circuit only partially converts the DC voltage present on the voltage source side into an AC voltage.

[0007] This invention is particularly based on the concept that, in cases where the effectiveness or efficiency of inversion and power transmission is poor or low, this problem is overcome by operating the inverter circuit in a half-bridge mode. That is, the conditions under which poor effectiveness is expected are, in particular, a high DC voltage value on the voltage source side and a low power value to be transmitted. To solve or avoid this problem, in half-bridge mode, only a portion of the DC voltage is converted to AC voltage, which results in a significant improvement in effectiveness or efficiency. Therefore, within the scope of this invention, an active inverter circuit, i.e., a controllable inverter circuit, is provided that selectively enters either a half-bridge mode or a full-bridge mode by means of a corresponding control signal.

[0008] The motor may include a housing arranged in a motor vehicle in a manner fixed to the vehicle body, wherein the stator components are fixedly mounted in the housing. The rotor may be connected to the stator, specifically the housing, via at least one rotary bearing (which may be a ball bearing or a roller bearing). For this purpose, the rotor shaft may be rotatably arranged on both sides in corresponding rotary bearings.

[0009] The transmission coil can have or be made of windings of conductive wire, which are energized by an AC voltage generated by an inverter circuit. In the transmission coil, an electromagnetic field forms and dissipates periodically, and this time-varying magnetic field enables power to be transferred to the coil in an inductive manner.

[0010] According to the present invention, the inverter circuit includes a full-bridge circuit and a half-bridge circuit. In terms of the relevant circuit diagram, the full-bridge circuit is H-shaped, wherein two series-connected transistors are arranged in each of the two vertical branches of this shape. The horizontal branch connecting the two vertical branches is often also referred to as the bridge branch. The half-bridge circuit includes two series-connected transistors. The transistors are semiconductor structural elements, preferably metal-oxide-semiconductor field-effect transistors (MOSFETs) and / or insulated-gate bipolar transistors (IGBTs). Therefore, in order to control the circuit state of the transistors, a corresponding gate voltage is applied to the corresponding transistor to cause the transistor, in particular, to enter a conducting state or a blocking state.

[0011] Preferably, the full-bridge circuit comprises two pairs of series-connected full-bridge transistors connected in parallel, wherein a coil node is arranged between each pair of full-bridge transistors, and at least one stator-side transmission coil is connected between the two coil nodes. Each pair of full-bridge transistors can be connected to each other such that the source connection of one full-bridge transistor is connected to the drain connection of the corresponding other full-bridge transistor, with the coil node located between them. A line branching from each of the coil nodes leads to a transmission coil, thereby integrating the transmission coil into the bridge branch.

[0012] A half-bridge circuit may include two half-bridge transistors connected in series, wherein a half-bridge node is arranged between one of the pairs of full-bridge transistors, and the half-bridge circuit is connected to the full-bridge circuit through the half-bridge node. The half-bridge transistors can be interconnected such that the source connection of one half-bridge transistor is connected to the source connection of the other half-bridge transistor.

[0013] Preferably, to achieve the half-bridge operating mode of the inverter circuit, a control signal is generated by a control device such that the half-bridge transistors remain continuously turned on, while the full-bridge transistors with half-bridge nodes arranged between them remain continuously turned off. Therefore, in the half-bridge operating mode, only one pair of full-bridge transistors (including two full-bridge transistors) is used for inversion, thereby supplying only half of the theoretically available voltage to the given sub-side transmission coils.

[0014] It is conceivable that, in order to achieve full-bridge operation of the inverter circuit, a control signal would be generated by a control device to keep the half-bridge transistors in a continuously non-conducting state. In this case, two pairs of full-bridge transistors (each consisting of two full-bridge transistors) would be used for inversion in full-bridge operation, thereby supplying essentially all available voltage to the given transformer-side transmission coils.

[0015] As already mentioned, control signals configured to control the transistors are generated on the control device side. For the relevant control basis, it can be stipulated that control signals are generated by means of the control device based on power information relating to the power currently to be transmitted to the rotor via the stator-side transmission coils and / or voltage information relating to the current DC voltage of the voltage source, such that the inverter circuit is either in half-bridge operating mode or in full-bridge operating mode. The power information may be or includes a digital value (e.g., in watts) indicating the current power to be transmitted. The voltage information may be or includes a digital value (e.g., in volts) indicating the current DC voltage value. The determination of the power information and / or voltage information can be achieved through sensors, i.e., through measurement techniques. Furthermore or alternatively, it is conceivable to provide control commands to a control unit configured to control the operation of the motor, wherein the power information and / or voltage information are determined according to the control commands. The control device may be or includes this control unit.

[0016] Preferably, the control signal is generated by the control device such that if the power information indicates that the power to be transmitted is less than a power threshold / limit, the inverter circuit operates in half-bridge mode; and if the power information indicates that the power to be transmitted is greater than the power threshold, the inverter circuit operates in full-bridge mode. Therefore, the power threshold provides a decision criterion for the corresponding operation. Alternatively, it is conceivable that the control signal is generated by the control device such that if the voltage information indicates that the current DC voltage is less than a voltage threshold, the inverter circuit operates in half-bridge mode; and if the voltage information indicates that the current DC voltage is greater than the voltage threshold, the inverter circuit operates in full-bridge mode. Therefore, the voltage threshold provides a decision criterion for the corresponding operation. It is also conceivable that the power threshold is related to the voltage threshold, and / or vice versa.

[0017] Within the scope of a conceivable improvement scheme, it is specified that, not only for half-bridge operating mode but also for full-bridge operating mode, there exist comprehensive characteristic curves relating to the inverter circuit efficiency and / or to the power transfer efficiency from stator to rotor, where the value at which these comprehensive characteristic curves intersect is used as a power threshold for the current power value to be transmitted. Alternatively, it is conceivable that, not only for half-bridge operating mode but also for full-bridge operating mode, there exist comprehensive characteristic curves relating to the inverter circuit efficiency and / or to the power transfer efficiency from stator to rotor, where the value at which these comprehensive characteristic curves intersect is used as a voltage threshold for the current DC voltage value. If only one of the above two alternatives is implemented, the comprehensive characteristic curve is a single characteristic curve where the obtained efficiency is related to either power or voltage. Particularly preferred is the implementation of both alternatives, so that the obtained efficiency is related to both variables. In this case, the correlation exists in a three-dimensional manner, where for each pair of power and voltage values, the associated obtained efficiency value is known separately. The comprehensive characteristic curves can be stored on the storage device side as a corresponding value table or lookup table, and the storage device can be the storage medium of the control device.

[0018] To specifically check whether to select half-bridge or full-bridge operating mode, it is conceivable to determine the relevant efficiency values ​​for the two modes based on the corresponding (multiple) pieces of information involving power and / or voltage, and then select the operating mode with the larger efficiency value.

[0019] Furthermore, the present invention relates to a control device. In such a control device, according to the invention, the aforementioned objective is achieved by having a computer-readable storage medium storing executable instructions, which, when executed by means of a control device designed as a computer, cause a processing unit of the control device to generate and output a control signal that triggers the execution of at least one of the steps of the method described above. All features, advantages, 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.

[0020] In the control device according to the invention, it is conceivable that the control device is adapted to generate and output control signals for controlling the transistors of the half-bridge circuit and the full-bridge circuit, the control signals representing, for example, the corresponding gate voltages, so that the inverter circuit can operate in a low-voltage operating mode and in a full-bridge operating mode, in which the voltage present on the voltage source side is fully applied to the full-bridge circuit, and in the half-bridge operating mode, the voltage present on the voltage source side is only partially applied to the full-bridge circuit.

[0021] Furthermore, the present invention relates to an inverter circuit. Here, according to the invention, the aforementioned objective is achieved by means of an inverter circuit that can be used in the method described above, wherein a DC voltage from a voltage source can be converted to an AC voltage by means of the inverter circuit and output to at least one stator-side transmission coil, wherein the inverter circuit includes a full-bridge circuit, which is connected to or may be connected to a voltage source via a half-bridge circuit on one hand, and to or may be connected to at least one stator-side transmission coil on the other hand. All features, advantages, and aspects explained in conjunction with the method according to the invention and the control device according to the invention can be similarly transferred to the inverter circuit according to the invention, and vice versa.

[0022] Furthermore, the present invention relates to a stator for an electric motor used in a motor vehicle. Here, according to the invention, the object is achieved by the stator including the inverter circuit described in the foregoing description. Preferably, the stator also includes a control device described in the foregoing description. Alternatively, the control device may be a component of the electric motor or the motor vehicle. All features, advantages, and aspects explained in conjunction with the method according to the invention, the control device according to the invention, and the inverter circuit according to the invention can be equally transferred to the stator according to the invention, and vice versa.

[0023] Furthermore, the present invention relates to an electric motor for motor vehicles. In this motor, according to the invention, the aforementioned objective is achieved by comprising a stator as described above and a rotor supported in a manner rotatable relative to the stator, the rotor having rotor windings for generating a rotor magnetic field. All features, advantages, and aspects of the method according to the invention, the control device according to the invention, the inverter circuit according to the invention, and the stator explanation according to the invention can be similarly transferred to the motor according to the invention, and vice versa.

[0024] Preferably, the motor according to the invention has an induction-type rotary transformer, which includes at least one rotor-side transmission coil present on the rotor side and at least one stator-side transmission coil present on the stator side, wherein power can be inductively transmitted to at least one rotor-side transmission coil for energizing the rotor windings by means of at least one stator-side transmission coil. The induction-type rotary transformer enables contactless and therefore low-wear or wear-free power transmission from the stator to the rotor. The rotor-side transmission coil and the stator-side transmission coil move past each other during rotor rotation, wherein the magnetic field generated at the stator-side transmission coil ends induces a voltage at the rotor-side transmission coil ends by means of electromagnetic induction. Therefore, the rotor-side transmission coil serves as a voltage source, wherein the generated voltage is in the form of an alternating current voltage. Preferably, a plurality of transmission coils are arranged concentrically about the rotor's axis of rotation and thus circumferentially.

[0025] It is conceivable that at least one rotor-side transmission coil is connected to the rotor winding via a rectifier circuit, wherein the AC voltage present on the side of at least one rotor-side transmission coil can be converted into the DC voltage required to generate the rotor magnetic field by means of the rectifier circuit. Preferably, the rectifier circuit includes electrical components, such as transistors. Here, the rectifier circuit can be manipulated by means of a control signal, which is generated, for example, by means of a control device, wherein the control signal is intended to control the operation of the rectifier circuit, i.e., to perform rectification. Therefore, preferably, the rectifier circuit is an active rectifier circuit, which, compared to a passive rectifier circuit, not only has passive structural elements (such as semiconductor diodes) but also controllable components (such as transistors). The AC voltage present on the output side of the rectifier circuit is supplied to the rotor winding to generate the rotor magnetic field.

[0026] Preferably, bidirectional power transfer is achieved using a rotary transformer. This demagnetization of the rotor windings, i.e., elimination of the rotor magnetic field present on the rotor winding side, is accomplished by converting the DC voltage present on the rotor winding side into an AC voltage using a rectifier circuit. Energy stored in the rotor windings is then transferred from the rotor-side transmission coil to the stator-side transmission coil via induction. For this purpose, the rectifier circuit is brought into a state by a corresponding control signal, in which the DC voltage present on the rotor winding side is converted into an AC voltage, which is then applied to the rotor-side transmission coil. Accordingly, power is directed to the stator-side transmission coil, and the power is then supplied to the vehicle's energy storage unit via an inverter circuit that functions as the rectifier circuit in this case.

[0027] Since the control device is typically located at a different position than the rotor, but the control signals from the control device are also used to control the rectifier circuit on the rotor side, it is necessary to transmit control commands from the stationary section of the motor, particularly 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 and at least one stator-side communication coil. Control commands generated by the control device for controlling the operation of the rectifier circuit can be inductively transmitted 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] Preferably, the motor according to the invention is connected to or can be connected to the powertrain of a motor vehicle, wherein, in the connected state, traction torque can be generated by means of the motor and transmitted to the wheels of the motor vehicle through 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 particularly non-rotatable mechanical connection 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 may include a drive shaft and / or a transmission, particularly a shift transmission and / or a differential and / or a clutch.

[0029] Finally, the present invention relates to a motor vehicle including a traction motor. In this motor vehicle, according to the invention, the aforementioned objective is achieved by the traction motor being a motor as described in the foregoing descriptive paragraphs. All features, advantages, and aspects explained in conjunction with the method according to the invention, the control device according to the invention, the inverter circuit according to the invention, the stator according to the invention, and the motor according to the invention can be similarly transferred to the motor vehicle according to the invention, and vice versa.

[0030] Preferably, the motor vehicle according to the invention includes an electric energy storage device in which energy usable for towing the motor vehicle can be stored. This energy is in the form of electrical energy and is converted into kinetic energy by means of an electric motor. Conversely, it is conceivable that the electric motor operates in a regeneration mode, in which the kinetic energy of the motor vehicle is converted into electrical energy stored in the energy storage device. A DC voltage source can be provided by means of the energy storage device (which can be, in particular, a lithium-ion battery). Attached Figure Description

[0031] Other advantages and details of the invention are illustrated in the following embodiments and given with reference to the accompanying drawings. Wherein, schematically:

[0032] Figure 1 A schematic diagram of a motor vehicle according to an embodiment of the invention, shown in a side view, is illustrated. The motor vehicle includes a motor according to an embodiment of the invention and a control device according to an embodiment of the invention. The stator has a stator according to an embodiment of the invention. The method according to an embodiment of the invention is explained according to this motor vehicle.

[0033] Figure 2 It shows Figure 1 A schematic, circuit diagram of the height of a motor in a motor vehicle.

[0034] Figure 3 It shows Figure 2 This is a portion of the schematic diagram, showing the rectifier circuit in full-bridge operation mode.

[0035] Figure 4 It shows Figure 2 A portion of the schematic diagram, showing the rectifier circuit in half-bridge operating mode, and

[0036] Figure 5 A coordinate system is shown to illustrate the relationship between efficiency and power. Detailed Implementation

[0037] Figure 1 A motor vehicle 1 according to an embodiment of the invention is shown, comprising a traction motor, which is a motor 2 according to an embodiment of the invention. The motor 2 includes a rotor 3 and a stator 4 according to an embodiment of the invention. The motor 2 is an internal rotor, designed as a separately excited synchronous motor. Therefore, the rotor 3 is arranged in a region further inward in the radial direction of the 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 motor 2, for example by means of ball bearings or roller bearings.

[0038] 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.

[0039] 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 vertically to longitudinal direction 10. Circumferential direction 12 extends vertically to radial direction 11. In other words, the point of rotation about axis 9 moves along circumferential direction 12.

[0040] The following explains the details regarding motor 2. Figure 2A highly schematic circuit diagram of motor 2 is shown, illustrating the distribution of motor 2 components on rotor 3 and stator 4. Therefore, an inverter circuit 13 is provided on the stator 4 side, by means of which the DC voltage supplied at the energy storage terminal 7 on or through the voltage source 16 of motor 2 is converted to AC voltage. In this example, inverter circuit 13 includes a printed circuit board on which electronic components of inverter circuit 13 are arranged, and in particular soldered. To control the operation of inverter circuit 13, a control device 14 according to one embodiment of the invention is provided, adapted to generate control signals or corresponding control voltages for controlling the operation of inverter circuit 13 and output them to the inverter circuit. Although control device 14 is shown as a component of motor 2 in this example, it could also be located outside motor 2 and thus be a component of motor vehicle 1. By means of the AC voltage generated by inverter circuit 13, the stator windings of stator 4 (not shown in detail in the figure) and rotor windings 15 of rotor 3 (in...) can be controlled. 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.

[0041] The details regarding the transfer of electrical energy or power from the energy storage unit 7 or voltage source 16 to the stator winding 15 will now be explained. First, the DC voltage supplied at the energy storage unit 7 or present at the voltage source 16 is converted to AC voltage using the inverter circuit 13. This AC voltage is then transmitted to the stator-side transmission coil 17 located on the stator 4 side, through which energy is inductively transferred to the rotor-side transmission coil 18 located on the rotor 3 side. Therefore, the excitation coils 17 and 18 form an inductive rotary transformer 19, through which contactless energy transfer from the fixed section of the stator 4 or motor 2 to its rotor 3 is achieved.

[0042] The excitation coil 18 on the rotor side realizes a voltage source present on the rotor 3 side, on which an AC voltage exists. This AC voltage is supplied to the rectifier circuit 20 of the rotor 3, and the rectifier current converts the AC voltage into a DC voltage. The rectifier circuit 20 connects the rotor-side transmission coil 18 to the rotor winding 15, thereby supplying the voltage provided by the rotor-side transmission coil 18 and converted into a DC voltage by means of the rectifier circuit 20 to the rotor winding 15 to generate a rotor magnetic field. The active rectifier circuit 20 includes multiple, i.e., four transistors, which are not all labeled in the figure for visibility reasons, and in this example are metal-oxide-semiconductor field-effect transistors. The rectification of the AC voltage provided by the rotor-side excitation coil 18 is performed according to a control voltage generated at the control device 14, which is applied to one of the field-effect transistors of the rectifier circuit 20.

[0043] Therefore, in addition to generating the control signals set for the inverter circuit 13, the control device 14 is also adapted to generate the control signals mentioned above for controlling the operation of the active rectifier circuit 20, and output them to the active rectifier circuit via an inductive communication rotary transformer (not shown in detail). The communication rotary transformer includes a stator-side communication coil located on the stator 4 side and a rotor-side communication coil located on the rotor 3 side. The control signals from the control device 14, set for the operation of the rectifier circuit 20, are transmitted inductively from the stator-side communication coil to the rotor-side communication coil, and then immediately to the transistors of the rectifier circuit 20. The operating principle of the communication rotary transformer is essentially the same as that of the rotary transformer 19.

[0044] To implement the method according to one embodiment of the invention as explained below, control device 14 is adapted to generate corresponding control signals intended to perform the method. For this purpose, control device 14 includes a computer-readable storage medium 21 storing executable instructions 22, which, when executed by a processing device 23 of control device 14, cause the processing device to perform steps defined in the context of this method. Specifically, control signals are generated by means of control device 14 and applied as gate voltages to transistors 25-28, 31, and 32 of inverter circuit 13. For clarity, the corresponding connection lines are not shown in the figures.

[0045] However, we will first provide a further explanation of the details of the inverter circuit 13. Specifically, the inverter circuit includes a full-bridge circuit 24, which in turn includes two pairs of series-connected full-bridge transistors 25-28 connected in parallel. Between each pair of full-bridge transistors 25-28, a coil node 29 is provided, through which the stator-side transmission coil 17 is connected. Furthermore, the inverter circuit 13 includes a half-bridge circuit 30 connected to the full-bridge circuit 24, which includes two series-connected half-bridge transistors 31 and 32. Between one pair of full-bridge transistors 25 and 26, a half-bridge node 33 is arranged, through which the half-bridge circuit 30 is connected to the full-bridge circuit 24.

[0046] In the first step of this method, voltage information relating to the current DC voltage value on the voltage source 16 is acquired. Additionally, power information relating to the power value that should currently be transmitted to the rotor-side transmission coil 18 via the stator-side transmission coil 17 is acquired. The voltage and power information are determined based on control commands generated by the control device 14 for controlling the operation of the motor 2. Alternatively, the information can also be acquired via sensors.

[0047] In the next step of the method, based on the voltage and power information, it is determined whether the rectifier circuit 13 should operate in half-bridge or full-bridge mode. For this purpose, the expected efficiency value associated with the inversion performed by the inverter circuit 13 and the power value transmitted by the resolver 19 are determined. These values ​​are then compared, with the inverter circuit 13 operating in the mode with the higher expected efficiency.

[0048] The specific operational procedures related to the comparison of efficiency values ​​are explained below. Two composite characteristic curves, 35 and 36, are known, representing the correlation between expected efficiency and voltage and power values ​​(i.e., voltage and power information) in each of the two operating modes. In this example, composite characteristic curves 35 and 36 form three-dimensional data sets. The known composite characteristic curves 35 and 36 are stored on the control device 14 in the form of a lookup table—Table 34—and have already been determined during measurement and / or calculation and / or modeling. In this example, it is assumed that the voltage information indicates a current voltage value of 920V at the voltage source 16. Figure 5 A coordinate system is shown relating the constant voltage value of 920V to the intersection of two composite characteristic curves 35 and 36. Therefore, the intersection of composite characteristic curves 35 and 36 generates two characteristic lines, where the characteristic line obtained from composite characteristic curve 35 corresponds to the full-bridge operating mode, and the characteristic line obtained from composite characteristic curve 36 corresponds to the half-bridge operating mode.

[0049] Figure 5The coordinate system comprises a horizontal axis 37 relating to power values ​​and a vertical axis 38 relating to efficiency values, wherein the characteristic lines intersect at a specific power value (hereinafter referred to as power threshold 39). Below power threshold 39, the efficiency value in half-bridge operating mode is higher than that in full-bridge operating mode. Above power threshold 39, the efficiency value in full-bridge operating mode is higher than that in half-bridge operating mode. It should be noted that the operational procedure already explained regarding the intersection of the comprehensive characteristic curves 35 and 36 can also be applied to constant values ​​of voltage information, where, similarly, the corresponding voltage threshold is obtained. In this case, vertical axis 38 relates to voltage values ​​rather than power values.

[0050] Subsequently, control signals or gate voltages are generated by means of control device 14 and output to inverter circuit 13, specifically transistors 25-28, 31, and 32, such that if the power information indicates that the power to be transmitted is less than the power threshold 39, inverter circuit 13 is in half-bridge operating mode, and if the power information indicates that the power to be transmitted is greater than the power threshold 39, inverter circuit 13 is in full-bridge operating mode.

[0051] The following is for reference. Figure 3 and Figure 4 ,in, Figure 3 The circuit diagram of inverter circuit 13 in full-bridge operating mode is shown, while Figure 4 The circuit diagram of inverter circuit 13 in half-bridge operation mode is shown. In full-bridge operation mode, a control signal is generated by control device 14 such that the two half-bridge transistors 31 and 32 are continuously in a blocking state, thus forming a high resistance 40 that prevents current from flowing through the half-bridge transistors 31 and 32. For the four full-bridge transistors 25-29, a control signal is generated such that the full-bridge transistors are continuously in a conducting state except for the blocking state required during inversion. Therefore, in full-bridge operation mode, inverter circuit 13 completely converts the DC voltage present on the voltage source 16 side into an AC voltage that should be returned to the stator side transmission coil 17.

[0052] In half-bridge operation mode, control signals are generated by control device 14 such that the two half-bridge transistors 31 and 32 remain continuously conducting, while the two full-bridge transistors 25 and 26, with half-bridge node 33 between them, remain continuously blocking, thus forming a high resistance 40 that prevents current from flowing through the full-bridge transistors 25 and 26. For the other two full-bridge transistors 27 and 28, control signals are generated such that these two full-bridge transistors remain continuously conducting except for the blocking state required during inversion. Clearly, in half-bridge operation mode, inversion is performed such that the inverter circuit 13 converts only a portion (i.e., half in this example) of the DC voltage present on the voltage source 16 side into an AC voltage that should be returned to the stator-side transmission coil 17.

Claims

1. A method for operating 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 field, wherein an inverter circuit (13) is provided on the stator (4) side, by means of which a direct voltage of a voltage source (16) is converted into an alternating voltage and output onto at least one stator-side transmission coil (17), wherein power is inductively transferred to the rotor (3) by means of the stator-side transmission coil (17) for energizing the rotor winding (15), characterized in that the inverter circuit (13) comprises a full-bridge circuit (24), which is connected to the voltage source (16) on the one hand by means of a half-bridge circuit (30) and to the at least one stator-side transmission coil (17) on the other hand, wherein control signals for controlling the transistors (25-28, 31, 32) of the half-bridge circuit (30) and of the full-bridge circuit (24) are generated and output by means of a control device (14) in order to operate the inverter circuit (13) either in a full-bridge operating mode, in which the direct voltage present on the voltage source (16) side is completely converted into an alternating voltage by means of the inverter circuit (13), or in a half-bridge operating mode, in which the direct voltage present on the voltage source (16) side is only partially converted into an alternating voltage by means of the inverter circuit (13).

2. The method of claim 1, wherein, The full-bridge circuit (24) comprises two pairs of full-bridge transistors (25-28) connected in series, which are connected in parallel, wherein a coil node (29) is arranged between the full-bridge transistors (25-28) of each pair, wherein the at least one stator-side transmission coil (17) is connected between two coil nodes (29).

3. The method of claim 2, wherein, The half-bridge circuit (30) comprises two half-bridge transistors (31, 32) connected in series, wherein a half-bridge node (33) is arranged between one pair of the full-bridge transistors (25, 26), the half-bridge circuit (30) being connected to the full-bridge circuit (24) via the half-bridge node.

4. The method of claim 3, wherein, In order to realize the half-bridge operating mode of the inverter circuit (13), the control signals are generated by means of the control device (14) such that the half-bridge transistors (31, 32) are continuously in a conducting state and the full-bridge transistors (25-28) between which the half-bridge node (33) is arranged are continuously in a non-conducting state.

5. The method according to claim 3 or 4, characterized in that, In order to realize the full-bridge operating mode of the inverter circuit (13), the control signals are generated by means of the control device (14) such that the half-bridge transistors (31, 32) are continuously in a non-conducting state.

6. The method according to any of the preceding claims, characterized in that, The control signals are generated by means of the control device (14) depending on power information relating to the power which is currently to be transferred to the rotor (3) by means of the stator-side transmission coil (17) and / or voltage information relating to the current direct voltage of the voltage source (16) such that the inverter circuit (13) is either in the half-bridge operating mode or in the full-bridge operating mode.

7. The method of claim 6, wherein, The control signals are generated by means of the control device (14) such that - the inverter circuit (13) is brought into the half-bridge mode of operation if the power information indicates that the power to be transmitted at present is less than a power threshold value (39), and into the full-bridge mode of operation if the power information indicates that the power to be transmitted at present is greater than the power threshold value (39), and / or - the inverter circuit (13) is brought into the half-bridge mode of operation if the voltage information indicates that the direct voltage present at present is less than a voltage threshold value, and into the full-bridge mode of operation if the voltage information indicates that the direct voltage present at present is greater than the voltage threshold value.

8. The method as claimed in claim 7, characterized in that - there is a combined characteristic curve (35, 36) relating to the efficiency of the inverter circuit (13) and / or to the efficiency of the power transmission from the stator (4) to the rotor (3) in relation to the power to be transmitted at present, not only for the half-bridge mode of operation but also for the full-bridge mode of operation, wherein the value at which the combined characteristic curves (35, 36) intersect here is used as the power threshold value (39) for the power value to be transmitted at present, and / or - there is a combined characteristic curve (35, 36) relating to the efficiency of the inverter circuit (13) and / or to the efficiency of the power transmission from the stator (4) to the rotor (3) in relation to the direct voltage present at present, not only for the half-bridge mode of operation but also for the full-bridge mode of operation, wherein the value at which the combined characteristic curves (35, 36) intersect here is used as the voltage threshold value for the direct voltage value present at present.

9. A control device (14) having a computer-readable storage medium (21) on which instructions (22) are stored, which, in the case of execution of the instructions by means of the control device (14) designed as a computer, prompt a processing device (23) of the control device (14) to generate and output control signals which initiate the implementation of at least one of the steps of the method according to any of the preceding claims.

10. An inverter circuit (13) for use in the method according to any one of claims 1 to 8, wherein By means of the inverter circuit (13), the direct voltage of the voltage source (16) can be converted into an alternating voltage, and this alternating voltage can be output to the at least one stator-side transmission coil (17), wherein the inverter circuit (13) comprises a full-bridge circuit (24) which is connected or connectable to the voltage source (16) on the one hand by means of a half-bridge circuit (30) and to the at least one stator-side transmission coil (17) on the other hand.

11. A stator (4) for an electric machine (2) of a motor vehicle (1), comprising an inverter circuit (13) according to claim 10, and preferably a control device (14) according to claim 9.

12. An electric machine (2) for a motor vehicle (1), comprising a stator (4) according to claim 11 and a rotor (3) which is rotatably supported relative to the stator (4) and has rotor windings (15) for generating a rotor magnetic field.

13. The electric machine (2) according to claim 12, characterized in that Having an inductive resolver (19) comprising at least one rotor-side transmission coil (18) present on the rotor (3) side and at least one stator-side transmission coil (17) present on the stator (4) side, wherein power can be transferred inductively by means of the at least one stator-side transmission coil (17) to the at least one rotor-side transmission coil (18) for energizing the rotor winding (15).

14. The electric machine (2) according to claim 13, characterized in that The at least one rotor-side transmission coil (18) is connected to the rotor winding (15) by means of a rectifier circuit (20), wherein an alternating voltage present at the at least one rotor-side transmission coil (18) can be converted by means of the rectifier circuit (20) into a direct voltage required for generating a rotor magnetic field.

15. Motor vehicle (1) comprising a traction electric machine, said traction electric machine being an electric machine (2) according to any one of claims 12 to 14.

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