Method for operating an inductive transmission device

Abstract

The invention relates to a method for operating an inductive transmission device (5) of an electric machine (3), in particular of a motor vehicle (1), comprising an inductive excitation device, in particular a stationary primary side (7), and a secondary side (8), in particular connected to a rotor of the electric machine (3), the inductive excitation device being operated at a defined switching frequency, an inductive excitation device is provided for inductively transmitting an electrical signal from the primary side (7) to the secondary side (8) by means of the inductive excitation device, the switching frequency of the inductive excitation device being varied, in particular during operation of the electric machine (3).

Description

Technical Field

[0001] The invention relates to a method for operating an inductive transmission device, in particular of an electric machine of a motor vehicle, comprising a primary side, in particular stationary, with 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 inductively transmit an electrical signal from the primary side to the secondary side by means of the inductive excitation device. Background Art

[0002] Inductive transmission devices and their methods of operation are basically known in the prior art. Usually, an electrical signal is generated, for example, at 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 by a converter, in particular a rectifier, which can be transmitted to the rotor coil of an electric motor of a motor vehicle in order to generate a defined magnetic field at the rotor via the rotor coil.

[0003] When generating the electrical signal on the primary side, the control device, for example an inverter, operates at a predetermined clock frequency or switching frequency. It is known that, depending on the load range of the electric machine or on how much power is to be transmitted by the inductive transmission device, certain losses occur. For example, frequency-dependent losses occur in the control device, in particular at the semiconductor components, which changes approximately proportionally to the switching frequency. In contrast, in full-load operation or operation in a high-load range of the electric machine, a relatively high clock frequency is advantageous for reducing the losses occurring there. Therefore, a compromise is usually made by predetermining a switching frequency that keeps the losses occurring over the entire operating range of the electric machine or the inductive transmission device as low as possible. Summary of the invention

[0004] The object of the present invention is to specify an improved method for operating an inductive transmission device compared to this, wherein in particular the efficiency is improved.

[0005] This object is achieved by a method having the features of claim 1. Advantageous embodiments are the subject matter of the dependent claims.

[0006] As described, the invention relates to a method for operating an inductive transmission device, in particular an electric motor of a motor vehicle. The electric motor of the motor vehicle can be designed, for example, as a traction drive or a drive. The electric motor can be designed, for example, as a separately excited motor. As also described above, the inductive transmission device has an inductive excitation device assigned to a primary side. The primary side is stationary, in particular with respect to the 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 can be moved relative to the primary side. Thus, an electrical signal can be inductively transmitted to the secondary side by means of the inductive excitation device.

[0007] The invention is based on the recognition that the switching frequency of an inductive excitation device can be varied, in particular during operation of an electric machine. The inductive excitation device can be connected to a control device, such as an inverter, or can be connected to a control device, or can have a control device which is designed to generate the electrical signal to be transmitted inductively at a defined switching frequency.

[0008] The switching frequency may be variable or can be varied. In contrast to the prior art described above, in which the switching frequency is usually set to be fixed and used in all operating states of the inductive transfer device, the present invention provides for varying the switching frequency. For example, different switching frequencies can be used for different situations in which the inductive transfer device is used. The switching frequency may be within different ranges, for example from a first range of the order of magnitude of about 10 kHz to a second range of up to 150 kHz. In principle, the switching frequency can be selected or varied arbitrarily.

[0009] Advantageously, the inductive excitation device can be operated at a first switching frequency in at least one first operating state and can be operated at a second switching frequency in at least one second operating state. The different operating states can differ, for example, in terms of the power demand or the power to be transmitted. For example, in the first operating state there can be a first power demand or a first power to be transmitted, and in the second operating state there can be a second power demand or a second power to be transmitted. The power to be transmitted can be, for example, the electrical power called up or required by the motor 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 be different from the second switching frequency used in the second operating state. The first switching frequency may, for example, be lower than the second switching frequency, or the first switching frequency may be higher than the second switching frequency. An equally arbitrary number of switching frequencies may be determined for an arbitrary number of operating states, so that in the respective operating state, a switching frequency corresponding thereto may be set or selected.

[0011] According to a refinement of the described method, the switching frequency can be set according to the electrical power transmitted or to be transmitted, in particular according to at least one power limit value. As described, different switching frequencies can be used for different operating states. Different operating states can differ, for example, in the electrical power to be transmitted or transmitted in the corresponding operating state. For example, a power limit value or at least one power limit value can be defined.

[0012] The power limit value or the plurality of power limit values ​​may delimit different operating states from one another. In other words, a first power limit value may be located between a first power range and a second power range. If the required or output power is below the power limit value, a first operating state may be assumed and a first switching frequency may therefore be used. If the power is above the first power limit value, a second operating state may be assumed and a second switching frequency may therefore be used. This description may be transferred accordingly to any number of operating states, power ranges and power limit values.

[0013] The described embodiment enables in particular a “block-by-block” or “step-by-step” change in the switching frequency. If a power limit value is exceeded or undershot, a corresponding change in the switching frequency to the relevant value is brought about.

[0014] The switching frequency can also be set continuously depending on the electrical power delivered or to be delivered. Unlike the "block-by-block" change described above, this design proposes to change the switching frequency continuously. This makes it possible to determine the best possible switching frequency for the specific power demand that exists, which can be used to deliver electrical power or inductively deliver electrical signals. It is thus not necessary to form a "block" and use it for a specific range of operating states or power values. Instead, a specific switching frequency can be determined and applied for each power value.

[0015] In principle, the relationship between the switching frequency and the power can be set or determined arbitrarily. For example, the switching frequency can be set linearly or based on at least one function. In this case, any functional relationship between the switching frequency and the power to be transmitted or the electrical signal to be transmitted can be set so that the switching frequency used enables the most efficient operation of the inductive transmission device. In this case, different functional relationships can also be achieved in different power ranges or different operating states, i.e., for example, 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 based on 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 measured in advance and stored, for example, in a table, in particular a so-called "lookup table". It can thus be determined in advance in which operating state or in which power range which switching frequency enables efficient operation. The switching frequency can then be set in this operating state or in this power range. A model can also be used, which models or simulates the switching frequency to be used. The model can, for example, be a model of an electric motor of a motor vehicle, so that various input values, such as the power to be called or the torque to be set at the electric motor, the speed of the electric motor and other parameters, are input or provided, and if necessary, the switching frequency to be set of the inductive transmission device can be output and the switching frequency can be set accordingly.

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

[0018] Here, the switching frequency can be set according to the described power requirements. For example, a lower switching frequency can be set for a relatively low load of the motor, and a relatively high switching frequency can be set for a relatively high load. For example, a first switching frequency can be used for a first power requirement, and a second switching frequency can be used 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, the minimum losses can be determined for the current or upcoming operating point and the switching frequency can be set as a function of the determined minimum losses. As described above, in principle, the operation of the inductive transmission device or the operation of the electrical component to which the inductive transmission device belongs can be simulated. For this purpose, the current or upcoming operating point can be simulated and it can be determined for which switching frequency of the inductive transmission device what losses are to be expected or what losses occur during such operation. This allows the determination of the switching frequency for which the minimum losses occur. The switching frequency can then be set at this operating point in order to achieve the most efficient operation possible.

[0020] In addition to the method, the invention also relates to an inductive transmission device, in particular for an electric motor of a motor vehicle, comprising a primary side, in particular stationary, with an inductive excitation device, and a secondary side, in particular connectable to or already connected to the rotor of the electric motor, wherein the inductive excitation device is designed to inductively transmit electrical signals from the primary side to the secondary side, wherein the inductive transmission device has a control device, which in particular includes a converter, which is designed to change the switching frequency of the inductive excitation device, in particular during operation of the electric motor. The invention also relates to an electric drive assembly, which comprises an electric motor and the inductive transmission device described above. The invention also relates to an axle drive, which comprises the described inductive transmission device and / or the described electric drive assembly. The invention also relates to a motor vehicle, which has the described inductive transmission device and / or the described electric drive assembly and / or the described axle drive.

[0021] All advantages, details and features described for the method can be fully transferred to the inductive transmission device, the electric drive assembly, the axle drive and the motor vehicle. The inductive transmission device has in particular all devices required for carrying out the method. In particular, the inductive transmission device has a control device which is designed to change or set the switching frequency of the inductive excitation device or the method can be carried out on this control device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be explained below according to embodiments with reference to the accompanying drawings. These drawings are schematic diagrams and:

[0023] Figure 1 A schematic diagram of a motor vehicle including an electric machine and an inductive transmission device is shown; and

[0024] Figure 2 A flow chart of a method for operating an inductive transmission device is shown. DETAILED DESCRIPTION

[0025] Figure 1 A purely schematic diagram of a motor vehicle 1 is shown, which has an electric drive assembly 2, which can be designed, for example, as an electric axle drive or as a component thereof. The electric drive assembly 2 has an electric motor 3, which is designed, for example, as a traction drive or drive for the motor vehicle 1. The electric motor 3 is supplied with electrical energy from an electrical energy storage device 4 or an arbitrary power source. The electrical energy is transmitted from the electrical energy storage device 4 to the electric motor 3 in the form of an electrical signal by means of an inductive transmission device 5.

[0026] In this embodiment, the inductive transmission device 5 is controlled by a control device 6. The control device 6 may be a central control device 6 or may be a separate control device 6 of the inductive transmission device 5. The control device 6 may be integrated into the inductive transmission device 5 or may be connectable thereto or already connected thereto.

[0027] 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 comprises, for example, a transmitter coil. The secondary side 8 is ultimately designed as a receiver side and has, for example, a receiver coil. The secondary side 8 can be connected to a component of the electric machine 3, in particular the rotor of the electric machine 3. For example, the secondary side 8 is supported in a rotatable manner relative to the primary side 7. Thus, the primary side 7 is stationary, while the secondary side 8 is movable relative thereto.

[0028] Depending on the actuation, the electrical signal can be inductively transmitted from the primary side 7, for example, via an air gap to the secondary side 8. To this end, the control device 6 controls the primary side 7 so that an electrical signal is generated as an alternating voltage or an alternating current, thereby achieving inductive transmission between the primary side 7 and the secondary side 8. As is known, a converter, in particular a rectifier, is provided on the secondary side 8, which forms a rectified electrical signal from the transmitted electrical signal, and the electrical signal is supplied to the motor 3, for example, to the rotor coil of the rotor of the motor 3.

[0029] In the embodiment shown, the inductive transmission device 5 is designed so that the switching frequency for operating the inductive transmission device 5, i.e., the switching frequency for generating the electrical signal in particular, is variable, i.e., can be changed. Different switching frequencies can thus be set. For example, as described below, different switching frequencies can be set for different operating states.

[0030] For example, the method starts in a block 9 in which an operating state of the motor vehicle 1 or of the electric drive assembly 2 or of the inductive transmission device 5 is determined. In this case, the operating state can be characterized, for example, by a power range, which is determined by the electrical power transmitted or to be transmitted by the inductive transmission device 5. For example, different operating states can be determined, in particular, as a function of at least one electrical power limit value. Depending on the value assumed by the electrical power to be transmitted or transmitted, one of the predefined operating states is assumed. It is also possible to characterize the operating state by the power to be transmitted or transmitted, without having to determine the operating state as a function of a power limit value.

[0031] The operating state can also be defined by further parameters, in particular the mechanical power requirement. For example, it can be determined how much mechanical power, for example in the form of torque, the electric machine 3 must provide in a specific operating state that is currently or may soon occur. Depending on which operating state is determined in block 9, the corresponding operating state value is transmitted to block 10.

[0032] In block 10, a switching frequency can then be determined, for example, at the control device 6, with which the primary side 7 is operated or with which an electrical signal for the primary side 7 is generated. For example, as described above, the switching frequency can be determined depending on the operating state that is present. In this case, different switching frequencies can be predetermined for different operating states, which, as described, can be delimited from one another by power limit values. Thus, if the operation is in a first operating state, a first switching frequency predetermined for this can be used. If the operation is in a second operating state, which is above or below the power limit value that delimits the first operating state from the second operating state, a predetermined second switching frequency can be used.

[0033] The switching frequency to be set or to be used can also be determined or calculated in block 10. Various functions, in particular continuous functions, can be stored here. Thus, the switching frequency can be calculated as a function of the power to be transmitted or the power required at the electric machine 3. For example, a model or simulation can also be performed on the control device 6. Here, a suitable switching frequency can be determined for the current or upcoming operating point.

[0034] If the switching frequency is determined in block 10, it can be transferred to block 11. In block 11, the switching frequency is set, in particular, at the control device 6 and an electrical signal for the primary side 7 is generated based on the set switching frequency.

[0035] The advantages, details and features described in the exemplary embodiments shown can be combined with one another in any desired manner, can be interchanged with one another and can be transferred to one another. The method described here can be carried out in particular on a motor vehicle 1 which in particular has an inductive transmission device 5 .

[0036] Reference numerals list

[0037] 1 Motor Vehicle

[0038] 2 Electric drive components

[0039] 3 Motor

[0040] 4 Energy storage

[0041] 5 Inductive transmission device

[0042] 6 Control device

[0043] 7 Primary side

[0044] 8 Secondary side

[0045] 9-11 box.

Claims

1. A method for operating an inductive transmission device (5) of an electric machine (3), in particular of a motor vehicle (1), comprising a primary side (7) with an inductive excitation device, in particular a stationary primary side (7) 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 inductively transfer an electrical signal from the primary side (7) to the secondary side (8) by means of the inductive excitation device, characterized in that the switching frequency of the inductive excitation device is varied, in particular during operation of the electric machine (3).

2. The method according to claim 1, characterized in that The inductive excitation device is operated at a first switching frequency in at least one first operating state and at a second switching frequency in at least one second operating state.

3. The method according to claim 1 or 2, characterized in that: The switching frequency is set as a function of the electrical power delivered or to be delivered, in particular as a function of at least one power limit value.

4. The method according to any one of the preceding claims, characterized in that The switching frequency is set continuously as a function of the electrical power delivered or to be delivered.

5. The method according to claim 4, characterized in that The switching frequency is set linearly or based on at least one function.

6. The method according to any one of the preceding claims, characterized in that The switching frequency is set as a function of at least one measurement and / or at least one model, in particular a simulation.

7. The method according to any one of the preceding claims, characterized in that The switching frequency is set as a function of at least one power component of the electric machine (3), in particular a torque requirement.

8. The method according to any one of the preceding claims, characterized in that Minimum losses are determined for a current or upcoming operating point, and the switching frequency is set as a function of the determined minimum losses.

9. An inductive transmission device (5), in particular for an electric machine (3) of a motor vehicle (1), comprising a primary side (7), in particular stationary, with an inductive excitation device, and a secondary side (8), in particular connectable or already connected to a rotor of the electric machine (3), wherein: The inductive excitation device is configured to inductively transfer an electrical signal from the primary side (7) to the secondary side (8), and is characterized in that: The inductive transmission device has a control device (6), which in particular comprises a converter and is designed to change a switching frequency of the inductive excitation device, in particular during operation of the electric machine (3).

10. An electrodynamic drive assembly (2) comprising an electric motor (3) and an inductive transmission device (5) according to claim 9.

11. Axle drive comprising an inductive transmission device (5) according to claim 9 and / or an electromotive drive assembly (2) according to claim 10.

12. Motor vehicle (1) comprising an inductive transmission device (5) according to claim 9 and / or an electric drive assembly (2) according to claim 10 and / or an axle drive according to claim 11.

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