Method for operating an inductive transmission device

Abstract

Method for operating an inductive transmission device (5), in particular an electric machine (3) of a motor vehicle (1), comprising a primary side (7) having an inductive excitation device, in particular stationary, and a secondary side (8) connected in particular to a rotor of the electric machine (3), wherein the inductive excitation device is operated at a defined switching frequency in order to transmit an electrical signal inductively from the primary side (7) to the secondary side (8) by means of the inductive excitation device, wherein the switching frequency of the inductive excitation device is changed, in particular during operation of the electric machine (3).

Description

[0001] The invention relates to a method for operating an inductive transmission device, in particular an electric machine of a motor vehicle, comprising a primary side, in particular a stationary one, having an inductive excitation device and a secondary side, in particular connected to a rotor of the electric machine, wherein the inductive excitation device is operated at a defined switching frequency in order to transmit an electrical signal inductively from the primary side to the secondary side by means of the inductive excitation device.

[0002] Inductive transmission devices and methods for operating them are generally known from the prior art. Typically, an electrical signal is generated, for example, by a primary-side control device, which is transmitted from the primary side, for example, a transmitter coil, to the secondary side, for example, a receiver coil. On the secondary side, an electrical signal is generated via a power converter, in particular a rectifier, which can be passed to the rotor coils of the motor vehicle's electric machine in order to generate a defined magnetic field via the rotor coils.

[0003] When generating the electrical signal for the primary side, the control device, for example an inverter, operates at a specified clock frequency or switching frequency. It is known that a certain loss occurs depending on the load range of the electrical machine or how much power is to be transmitted via the inductive transmission device. For example, frequency-dependent losses occur in the control device, particularly in semiconductor components, and these scale approximately proportionally with the switching frequency. On the other hand, when the electrical machine is operating at full load or in a high load range, a comparatively high clock frequency is advantageous in order to reduce the losses that occur there. A compromise is therefore usually made by specifying a switching frequency that covers the losses that occur over the entire operating range of the electrical machine orthe inductive transmission device as low as possible.

[0004] The invention is based on the object of providing an improved method for operating an inductive transmission device, in which in particular the efficiency is improved.

[0005] The object is achieved by a method having the features of claim 1. Advantageous embodiments are the subject of the subclaims.

[0006] As described, the invention relates to a method for operating an inductive transmission device, in particular for an electric machine of a motor vehicle. The electric machine of the motor vehicle can be designed, for example, as a traction drive or drive device. For example, the electric machine can be constructed as an externally excited electric machine. As also described above, the inductive transmission device has an inductive excitation device assigned to the primary side. The primary side is, in particular, stationary with respect to a rotational movement performed by the rotor of the electric machine. The transmission device has a secondary side that can be coupled to the rotor, i.e. the secondary side is movable relative to the primary side. By means of the inductive excitation device, an electrical signal can thus be transmitted inductively to the secondary side.

[0007] The invention is based on the finding that the switching frequency of the inductive excitation device is changed, particularly during operation of the electrical machine. The inductive excitation device can be connected to a control device, for example, an inverter, or can have such a control device, which is designed to generate the electrical signal, which is to be transmitted inductively, at a defined switching frequency.

[0008] The switching frequency can be variable or can be changed. In contrast to the previously described prior art, in which a fixed switching frequency is usually used in all operating states of the inductive transmission device, the present invention proposes changing the switching frequency. For example, different switching frequencies can be used for different situations in which the inductive transmission device is used. The switching frequencies can lie in different ranges, for example, in a first range on the order of approximately 10 kHz up to a second range of up to 150 kHz. In principle, the switching frequency can be freely selected or changed.

[0009] Advantageously, the inductive excitation device can be operated in at least one first operating state with a first switching frequency and in at least one second operating state with a second switching frequency. The various operating states can differ, for example, with respect to power requirements or power to be transmitted. For example, a first power requirement or first power to be transmitted can exist in a first operating state, and a second power requirement or second power to be transmitted can exist in a second operating state. The power to be transmitted can be, for example, the electrical power retrieved or requested from the electrical machine or the electrical power transmitted or to be transmitted by means of the inductive transmission device.

[0010] For example, in the first operating state, the first switching frequency may differ from the second switching frequency used in the second operating state. For example, the first switching frequency may be lower than the second switching frequency, or the first switching frequency may be higher than the second switching frequency. Any number of switching frequencies can be specified for any number of operating states, so that the corresponding switching frequency can be set or selected upon entering the respective operating state.

[0011] According to a further development of the described method, the switching frequency can be adjusted depending on the electrical power being transmitted or to be transmitted, in particular depending on at least one power limit. As described, different switching frequencies can be used for different operating states. The different operating states can differ, for example, in the electrical power being transmitted or to be transmitted in the respective operating state. For example, power limit values ​​or at least one power limit value can be defined.

[0012] The power limit or multiple power limits can differentiate between different operating states. In other words, a first power limit can lie between a first power range and a second power range. If the requested or output power is below the power limit, the first operating state can be present, and thus the first switching frequency can be used. If the power is above the first power limit, the second operating state can be present, and thus the second switching frequency can be used. The description can be applied accordingly to any number of operating states, power ranges, and power limits.

[0013] The described design enables, in particular, a "block-by-block" or "step-by-step" change in the switching frequency. If a power limit is exceeded or undershot, the switching frequency is adjusted accordingly to the corresponding value.

[0014] It is also possible for the switching frequency to be continuously adjusted depending on the electrical power being transmitted or to be transmitted. In contrast to the previously described "block-by-block" variation, the design proposes a continuous variation of the switching frequency. This makes it possible to determine the most optimal switching frequency for a specific power requirement, which can then be used for the transmission of the electrical power or the inductive transmission of the electrical signal. This eliminates the need to create "blocks" and use them for a specific range of operating states or power values. Instead, a specific switching frequency can be determined and used for each power value.

[0015] In principle, the relationship between the switching frequency and the power can be set or determined as desired. For example, the switching frequency can be set linearly or based on at least one function. Any functional relationship can be set between the switching frequency and the power to be transmitted or the electrical signal to be transmitted, so that the switching frequency used enables the most efficient operation of the inductive transmission device possible. Different functional relationships can also be implemented in different power ranges or different operating states, e.g. in a first operating state the switching frequency can be set based on a first function and in a second operating state the switching frequency can be set based on a second function.

[0016] The switching frequency can also be set as a function of at least one measurement and / or at least one model, in particular a simulation. For example, different switching frequencies for the operation of the inductive transmission device in different operating states can be pre-measured and stored, for example, in a table, in particular a so-called “lookup table”. This makes it possible to determine in advance which switching frequency enables efficient operation in which operating state or power range. The switching frequency can then be set when the operating state or power range is reached. It is also possible to use a model that models or simulates the switching frequency to be used. The model can, for example, be a model of the electric machine of the motor vehicle, so that different input values, for example the power called up ora torque to be set by the electrical machine, the speed and other parameters of the electrical machine are entered or supplied, and, if necessary, among other things, the switching frequency to be set of the inductive transmission device is output and the switching frequency can be set accordingly.

[0017] As described, the switching frequency is set to be variable, in particular so that, depending on the existing power requirement, a suitable switching frequency can be set that ensures the most efficient operation possible. The switching frequency can be set, for example, depending on at least one mechanical power requirement, in particular a torque requirement, of the electric machine. As described, the power requirement, for example, the torque to be provided by the electric machine in a driving state, can be determined or output, for example, by a control device or a central control device.

[0018] The switching frequency can be adjusted depending on the described power requirement. For example, lower switching frequencies can be set for comparatively low loads of the electrical machine, and comparatively high switching frequencies can be set for comparatively high loads. For example, a first switching frequency can be used for a first power requirement and a second switching frequency for a second power requirement, wherein the first switching frequency is different from the second switching frequency and the first power requirement is different from the second power requirement.

[0019] Furthermore, it is possible to determine a loss minimum for a current or future operating point and to adjust the switching frequency depending on the determined loss minimum. As previously described, it is fundamentally possible to simulate the operation of the inductive transmission device or the operation of the electrical arrangement to which the inductive transmission device is assigned. To do this, a current or future operating point can be simulated and it can be determined for which switching frequency of the inductive transmission device which losses are to be expected or which losses arise in such operation. This makes it possible to determine for which switching frequency a loss minimum occurs. The switching frequency that achieves the most efficient operation can then be set at the operating point.

[0020] In addition to the method, the invention relates to an inductive transmission device, in particular for an electric machine of a motor vehicle, comprising a primary side, in particular a stationary one, having an inductive excitation device, and a secondary side, in particular connectable or connected to a rotor of the electric machine, wherein the inductive excitation device is designed to inductively transmit an electrical signal from the primary side to the secondary side, wherein a control device, in particular comprising a power converter, is designed to change the switching frequency of the inductive excitation device, in particular during operation of the electric machine. Furthermore, the invention relates to an electric drive arrangement, comprising an electric machine and a previously described inductive transmission device.The invention further relates to an axle drive comprising a described inductive transmission device and / or a described electric drive arrangement. Furthermore, the invention relates to a motor vehicle having a described inductive transmission device and / or a described electric drive arrangement and / or a described axle drive.

[0021] All advantages, details, and features described with regard to the method are fully applicable to the inductive transmission device, the electric drive arrangement, the axle drive, and the motor vehicle. The inductive transmission device comprises, in particular, all devices required for implementing the method. In particular, the inductive transmission device comprises a control device designed to change or adjust the switching frequency of the inductive excitation device or on which the method can be implemented.

[0022] The invention is explained below using exemplary embodiments with reference to the figures. The figures are schematic representations and show: Fig. 1 shows a schematic diagram of a motor vehicle comprising an electric machine and an inductive transmission device; and Fig. 2 a flowchart of a method for operating an inductive transmission device.

[0023] Fig. 1 shows a purely schematic diagram of a motor vehicle 1 having an electric drive arrangement 2, which can be designed, for example, as an electric axle drive or a component thereof. The electric drive arrangement 2 has an electric machine 3, which is designed, for example, as a traction drive or drive device for the motor vehicle 1. The electric machine 3 is supplied with electrical energy by an electrical energy storage device 4 or any electrical energy source. The electrical energy is transmitted in the form of an electrical signal by means of an inductive transmission device 5 from the electrical energy storage device 4 to the electric machine 3.

[0024] In this exemplary embodiment, the inductive transmission device 5 is controlled by a control device 6. The control device 6 can be a central control device 6 or a separate control device 6 of the inductive transmission device 5. The control device 6 can be integrated into the inductive transmission device 5 or can be connected to it.

[0025] The inductive transmission device 5 has a primary side 7 and a secondary side 8. The primary side 5 has an inductive excitation device, which includes, for example, a transmitting coil. The secondary side 8 is ultimately designed as the receiving side and includes, for example, a receiving coil. The secondary side 8 can be connected to a component of the electrical machine 3, in particular the rotor of the electrical machine 3. The secondary side 8 is rotatably mounted relative to the primary side 7, for example. The primary side 7 is thus stationary, while the secondary side 8 is movable relative to it.

[0026] Depending on the control, an electrical signal can be transmitted inductively from the primary side 7, for example, via an air gap, to the secondary side 8. For this purpose, the control device 6 controls the primary side 7 such that the electrical signal is established as an alternating voltage or alternating current, thus enabling inductive transmission between the primary side 7 and the secondary side 8. As is known, a power converter, in particular a rectifier, is provided on the secondary side 8, which converts the transmitted electrical signal into a rectified electrical signal, which is fed to the electrical machine 3, for example, to the rotor coils of the rotor of the electrical machine 3.

[0027] In the illustrated embodiment, the inductive transmission device 5 is designed so that the switching frequency at which the inductive transmission device 5 is operated, ie, in particular, the switching frequency at which the electrical signal is generated, is variable, ie, can be changed. This results in different switching frequencies being able to be set. For example, as described below, a different switching frequency can be set for different operating states.

[0028] For example, the method starts in a block 9 in which the operating state of the motor vehicle 1 or of the electric drive arrangement 2 or of the inductive transmission device 5 is determined. The operating state can be characterized, for example, by a power range determined by the electrical power transmitted or to be transmitted by the inductive transmission device 5. For example, different operating states can be defined, in particular depending on at least one electrical power limit value. Depending on the value of the electrical power to be transmitted or being transmitted, one of the predefined operating states is thus present. It is also possible to characterize the operating state by the power to be transmitted or being transmitted, without this having to be defined depending on power limit values.

[0029] It is also possible to define the operating state using additional parameters, in particular a mechanical power requirement. For example, it can be determined what mechanical power the electric machine 3 must provide, for example in the form of torque, in a specific operating state, which may be current or future. Depending on which operating state was determined in block 9, a corresponding operating state value is transmitted to block 10.

[0030] In block 10, a switching frequency can then be determined, for example by the control device 6, by means of which the primary side 7 is operated or by means of which the electrical signal for the primary side 7 is generated. The switching frequency can, for example, be determined as a function of the specific operating state present, as described above. Different switching frequencies can be specified for different operating states, which, as described, can be differentiated from one another by power limit values. If operation is in a first operating state, a predetermined first switching frequency can be used for this purpose. If operation is in a second operating state which lies above or below a power limit value which differentiates the first from the second operating state, a predetermined second switching frequency can be used.

[0031] It is also possible to determine or calculate the switching frequency to be set or used in block 10. Various functions, particularly continuous functions, can be stored here. The switching frequency can thus be calculated depending on the power to be transmitted or the power requested by the electric machine 3. It is also possible, for example, to run a model or simulation on the control device 6. Suitable switching frequencies can be determined for current or future operating points.

[0032] Once the switching frequency has been determined in block 10, it can be transmitted to block 11. In block 11, the switching frequency is set, in particular by the control device 6, and the electrical signal for the primary side 7 is generated based on the set switching frequency.

[0033] The advantages, details, and features described in the exemplary embodiments shown can be combined with one another as desired, are interchangeable, and are transferable to one another. The method described herein can be implemented in particular on the motor vehicle 1, specifically with the inductive transmission device 5. Reference symbol 1 motor vehicle 2 electric drive arrangement 3 electric machine 4 electrical energy storage units 5 inductive transmission device 6 Control device 7 Primary page 8 Secondary side 9-11 Block

Claims

[1] Method for operating an inductive transmission device (5), in particular an electrical machine (3) of a motor vehicle (1), comprising a primary side (7) having an inductive excitation device, in particular a stationary one, and a secondary side (8), in particular connected to a rotor of the electrical machine (3), wherein the inductive excitation device is operated at a defined switching frequency in order to transmit an electrical signal inductively from the primary side (7) to the secondary side (8) by means of the inductive excitation device, characterized by that the switching frequency of the inductive excitation device is changed, in particular during operation of the electrical machine (3). [2] Method according to claim 1, characterized bythat the inductive excitation device is operated in at least one first operating state with a first switching frequency and in at least one second operating state with a second switching frequency. [3] Method according to claim 1 or 2, characterized by that the switching frequency is set as a function of an electrical power transmitted or to be transmitted, in particular as a function of at least one power limit value. [4] Method according to one of the preceding claims, characterized by that the switching frequency is continuously adjusted depending on the electrical power transmitted or to be transmitted. [5] Method according to claim 4, characterized by that the switching frequency is set linearly or based on at least one function. [6] Method according to one of the preceding claims, characterized bythat the switching frequency is set as a function of at least one measurement and / or at least one model, in particular a simulation. [7] Method according to one of the preceding claims, characterized by that the switching frequency is set as a function of at least one power arrangement, in particular a torque requirement, of the electrical machine (3). [8] Method according to one of the preceding claims, characterized by that a loss minimum is determined for a current or future operating point and the switching frequency is set depending on the determined loss minimum. [9] Inductive transmission device (5), in particular for an electrical machine (3) of a motor vehicle (1), comprising a primary side (7) having an inductive excitation device, in particular a stationary one, and a secondary side (8), in particular connectable or connected to a rotor of the electrical machine (3), wherein the inductive excitation device is designed to transmit an electrical signal inductively from the primary side (7) to the secondary side (8), characterized by a control device (6), in particular comprising a power converter, which is designed to change the switching frequency of the inductive excitation device, in particular during operation of the electrical machine (3). [10] Electric drive arrangement (2) comprising an electric machine (3) and an inductive transmission device (5) according to the preceding claim. [11] Axle drive comprising an inductive transmission device (5) according to claim 9 and / or an electric drive arrangement (2) according to the preceding claim. [12] Motor vehicle (1) comprising an inductive transmission device (5) according to claim 9 and / or an electric drive arrangement (2) according to claim 10 and / or an axle drive according to the preceding claim.

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