Rotor, separately excited synchronous motor and motor vehicle

Abstract

The invention relates to a rotor for a separately excited synchronous machine, comprising a rotor winding, a converter circuit and a secondary coil, the converter circuit comprising a first and a second secondary coil contact and a first and a second rotor winding contact and being designed to convert an alternating voltage induced in the secondary coil into a direct voltage in a first operating mode, the first and second secondary coil contacts are connected to the first rotor winding contact via a first line branch and to the second rotor winding contact via a second line branch in each case, the respective first and second line branches comprising a first and a second switching device, the switching devices are connected in series between the respective secondary coil contact and the respective rotor winding contact, each switching device comprises a semiconductor switch which comprises a body diode and / or a diode connected in parallel, and the diodes of the first switching device and the second switching device of the respective line branch have opposite conduction directions.

Description

Technical Field

[0001] This invention relates to a rotor for a separately excited synchronous motor, the rotor comprising rotor windings, a converter circuit, and a secondary coil. The converter circuit includes: a first secondary coil contact and a second secondary coil contact electrically connected to the secondary coil; a first rotor winding contact and a second rotor winding contact electrically connected to the rotor windings. The converter circuit is configured to, in a first operating mode, convert an AC voltage induced in the secondary coil and supplied via a secondary coil connection into a DC voltage, so as to apply a DC voltage to the rotor windings via the rotor winding connection to establish and / or maintain the rotor magnetic field. The first and second secondary coil contacts are respectively connected to the first rotor winding contact via a first line branch and to the second rotor winding contact via a second line branch. Furthermore, this invention relates to a separately excited synchronous motor and a motor vehicle. Background Technology

[0002] Compared to permanent magnet synchronous motors, separately excited synchronous motors contain no magnetic material in the rotor and generate their magnetic field by energizing the rotor windings. This provides additional degrees of freedom in motor adjustment and design, thereby improving efficiency and performance. This can be particularly important in situations where the motor is intended to drive motor vehicles, where high power is typically required while maintaining light weight and limited structural space.

[0003] Energization of the rotor windings is achieved, according to current technology, either via slip ring contacts or in a contactless manner via a power transmission system with an inductive rotary transformer. In the latter case, a stator-side inverter, an inductive rotary transformer comprising a primary winding on the stator side and a secondary winding on the rotor side, a rotor-side rectifier, and an optional filter for smoothing the excitation current are typically used to energize the rotor windings.

[0004] For efficiency reasons, it is usually appropriate to establish a high rotor magnetic field by using a high excitation current, because as the rotor magnetic field increases, a smaller alternating current is required in the stator coils to achieve the same torque as a synchronous motor.

[0005] Due to the typically high inductance of the rotor windings and the preferred high excitation current used, a large amount of energy is generated in the rotor during operation. Therefore, under certain operating conditions, such as in the event of an accident, it is appropriate to perform "rapid demagnetization" of the rotor windings; however, this requires additional circuitry on the rotor side to dissipate the energy. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a separately excited synchronous motor or an improved rotor for such a synchronous motor, which is particularly improved in terms of targeted elimination of the rotor magnetic field.

[0007] This objective is achieved by a rotor of the type described at the beginning, wherein the corresponding first and second line branches include a first switching device and a second switching device connected in series between corresponding secondary coil contacts and corresponding rotor winding contacts, wherein each switching device has a semiconductor switch comprising a body diode / parasitic diode, and / or a diode connected in parallel to the semiconductor switch, wherein the diodes of the first and second switching devices of the corresponding line branches have opposite conduction directions.

[0008] If both semiconductor switches in a line branch are switched to block, current flow through the line branch is thus blocked in both possible current flow directions. Conversely, if both semiconductor switches are switched to conduct, current can flow through the line branch, particularly with less resistance, in both current flow directions. In a switching state where only one of the semiconductor switches in the corresponding line branch is switched to block, a diode connected in parallel with that semiconductor switch, or the body diode, allows current to flow through the line branch only in the conduction direction of that diode.

[0009] According to the design scheme of the present invention, the converter circuit can not only be used in a first operating mode to receive energy through the secondary coil to establish a rotor magnetic field, but also in a second operating mode to actively eliminate the rotor magnetic field of the rotor winding and output or transfer the energy obtained from the rotor magnetic field through the secondary coil to the primary coil on the stator side. Thus, on the one hand, the rotor magnetic field can be eliminated quickly, and therefore the current flowing through the rotor winding can be reduced rapidly, which is suitable, for example, in the event of an accident, without requiring a dedicated rotor-side protection circuit, such as a clamping network. On the other hand, "returning energy to the primary coil on the stator side" enables the recovery of energy used to establish the rotor magnetic field, thereby improving the efficiency of the synchronous motor including the rotor.

[0010] Unlike the design according to the invention, in conventional active rectifiers used to supply current to the rotor windings, only a single semiconductor switch with a body diode or a parallel diode is used in the corresponding line branch. When a potential is applied to the rotor windings to establish or obtain the rotor magnetic field, a voltage is applied to this diode in the blocking direction. However, if active magnetic field elimination is to be achieved in this design, in order to achieve particularly rapid magnetic field elimination and / or recovery, the rotor windings and consequently the diodes must be energized in the opposite direction. However, as the reverse recovery voltage of the diode is reached, the diode carries current with low impedance, thus, in order to actively eliminate the magnetic field using conventional rotor-side converters to date, only a low voltage far below this reverse recovery voltage can be used to actively reduce the current flowing through the rotor windings.

[0011] The problem is avoided by using a series semiconductor switch according to the invention, which has parallel diodes or body diodes with opposite conduction directions, because, as mentioned above, the conduction or freewheeling path for each current direction can be controlled individually in this case.

[0012] The electrical connection between the secondary coil connection and the secondary coil, and the electrical connection between the rotor winding connection and the rotor winding, can be implemented directly or through other electrical components. For example, the rotor winding connection can be additionally connected via a buffer capacitor to reduce the ripple of the DC voltage applied to the rotor winding.

[0013] The corresponding semiconductor switch can be a MOSFET, which includes a body diode. A metal-oxide-semiconductor field-effect transistor (MOSFET) is a transistor with an insulated gate, and is therefore well-suited for high-current or high-voltage switching control. Because of the body diode, a separate freewheeling diode can be omitted, thus preventing voltage spikes when switching large winding currents. Furthermore, MOSFETs enable short switching times, minimizing switching losses, which is particularly important in converters that typically require high-frequency switching of semiconductor switches.

[0014] Furthermore, the present invention relates to a separately excited synchronous motor comprising a rotor according to the invention, wherein the rotor is rotatably supported on a stator, wherein the synchronous motor includes a power supply device configured to apply alternating current to the primary coil of the stator, thereby inducing an alternating voltage in the secondary coil of the rotor.

[0015] The power supply device may in particular be an inverter, which is powered by a DC voltage source, such as a battery, and may be located outside the synchronous motor, i.e., in a motor vehicle that includes a synchronous motor.

[0016] A pair of line branches, including one of the first line branches and one of the second line branches, can form a corresponding half-bridge between the first rotor winding contact and the second rotor winding contact. In the corresponding half-bridge, the conduction direction of the diode of the first switching device is from the second rotor winding contact to the first rotor winding contact. The synchronous motor may include a control device configured to, in a first operating mode, switch all semiconductor switches of the second switching devices to continuous conduction and switch the semiconductor switches of the first switching devices to intermittent conduction to rectify the AC voltage delivered via the secondary coil connection. Here, switching to intermittent conduction is understood as switching to alternating conduction and blocking, particularly switching in a periodic switching mode.

[0017] Because the conduction directions of the first switching device and the second switching device are opposite to each other, the conduction direction of the diode of the second switching device in the corresponding half-bridge is from the first rotor winding contact to the second rotor winding contact in the above case.

[0018] Therefore, in the first operating mode, the converter circuit can provide a positive potential at the first rotor winding contact relative to the potential applied at the second rotor winding contact, thereby increasing the current flowing through the rotor winding from the first rotor winding contact to the second rotor winding contact, or compensating for line losses. In the preceding and following description, the technical current direction is considered to be the direction of current flow.

[0019] Furthermore, the control device can be configured to, in the second operating mode, switch the semiconductor switches of all first switching devices to continuous conduction and switch the semiconductor switches of the second switching devices to intermittent conduction, so as to convert at least a portion of the DC current guided from the first rotor winding contacts to the second rotor winding contacts via the rotor windings into AC current supplied to the secondary coil, so as to guide energy from the rotor windings via the secondary and primary coils to the power supply device or to other components of the separately excited synchronous motor.

[0020] When energy is returned from the rotor windings to the stator, the current flowing through the rotor windings is actively reduced. Therefore, based on the current caused or maintained by the first operating mode, the potential applied to the second rotor winding contacts should be more positive than the potential applied to the first rotor winding contacts. Because the diodes connected in parallel with the semiconductor switches that are intermittently switched in the second operating mode block the current from the second rotor winding contacts to the first rotor winding contacts through the corresponding half-bridge in the technical current flow direction during the off-state of these semiconductors, a high reverse potential can be provided by the inverter circuitry used, and thus the current in the rotor windings is rapidly reduced or recovered.

[0021] The present invention also relates to a motor vehicle comprising a separately excited synchronous motor according to the invention. As already stated at the outset, high power density for motors is generally desirable in motor vehicles, and the additional degrees of freedom gained in motor design through the use of a separately excited synchronous motor are particularly advantageous. Furthermore, since a high rotor magnetic field strength can be advantageous in this case, the rapid reduction of rotor winding current achieved by the rotor or synchronous motor according to the invention is particularly important.

[0022] In at least one operating state of the motor vehicle, the synchronous motor can be mechanically connected to at least one wheel of the motor vehicle in such a way that the synchronous motor drives the wheel as a power device. Here, the corresponding wheel can be permanently connected to the synchronous motor, for example, in a single-wheel drive configuration. However, the synchronous motor can also drive multiple wheels of the motor vehicle via a transmission and / or differential, or it can be disengaged from these wheels.

[0023] The motor vehicle may include a DC on-board electrical grid, wherein the control device or a control device is configured to operate the power supply device, designed as another converter, as an inverter in a first operating mode to transfer energy to the rotor in an inductive manner, and to operate the power supply device as a rectifier in a second operating mode in which the rotor magnetic field of the rotor winding is actively eliminated to rectify the AC voltage induced in the primary coil and thereby feed energy into the DC on-board electrical grid.

[0024] Therefore, in particular, in the second operating mode, the energy recovered during the elimination of the rotor magnetic field can be used to charge the battery in the DC on-board grid and / or operate other components arranged there.

[0025] Specifically, in the second operating mode, the control device can manipulate the rotor-side converter circuit or its semiconductor switches as described above to actively reduce the rotor current. If the control device is part of the stator or is typically located outside the rotor, control signals for the rotor-side converter circuit can be transmitted inductively. Control of the semiconductor switches of the rotor-side converter circuit and / or the semiconductor switches of the stator-side converter can be achieved through electrically isolated gate drivers.

[0026] The control device can be configured to switch from a first operating mode to a second operating mode when a trigger condition is met, in order to actively eliminate the rotor magnetic field generated by the rotor windings. Preferably, the fulfillment of the trigger condition can depend on the presence of an accident and / or the presence of a synchronous motor shutdown process.

[0027] For example, an accident can be identified by a collision sensor or when the distance is below a limit detected by a distance sensor. Signals indicating an accident can also be provided by other vehicle systems, such as safety systems like airbag controls and seatbelt tensioners. In the event of an accident, components that may generate high voltage should be quickly switched to voltage-free conditions. In the case of coils with high inductance, i.e., for example, in rotor windings, active demagnetization of the coils is suitable, as can be achieved by means of a rotor, synchronous motor, or the design of the vehicle according to the invention.

[0028] When a synchronous motor is shut off, the rotor magnetic field should typically be reduced to zero. Therefore, in this case, "active reduction of coil current" is particularly suitable, especially in cases related to rotor magnetic field energy recovery. Attached Figure Description

[0029] Other advantages and details of the invention will become apparent from the following embodiments and the accompanying drawings. The drawings schematically illustrate:

[0030] Figure 1 Detailed diagrams are shown of an embodiment of a motor vehicle according to the present invention, the motor vehicle including an embodiment of a synchronous motor according to the present invention, the synchronous motor further including an embodiment of a rotor according to the present invention.

[0031] Figure 2 Shown in accordance with Figure 1 A detailed diagram of the converter circuit used in the rotor. Detailed Implementation

[0032] Figure 1A detailed view of a motor vehicle 33 is shown, in which one of the wheels 34 of the motor vehicle 33 and a separately excited synchronous motor 2 associated with the wheel 34 as a power device are shown. The direct connection between the rotor 1 of the synchronous motor 2 and the wheel 34 shown is purely exemplary. Alternatively, the synchronous motor 2 may drive the wheel 34 or more wheels, for example, through a transmission and / or a differential.

[0033] The synchronous motor 2 is powered by the DC on-board power grid 35 of the vehicle 33, which includes a battery 37 and additional DC components 38. For clarity, in... Figure 1 Only the part of the motor electronics used to energize the rotor winding 3 is shown. "Intermittently energizing the stator winding 40 to distribute torque to the rotor around the axis of rotation 27" can be achieved, for example, by a converter 36 on the stator side or a separate converter, not shown.

[0034] In the first operating mode of the synchronous motor 2, energy is transferred from the stator 26 to the rotor 1 in a contactless manner to enhance the rotor magnetic field by increasing the current guided through the rotor winding 3, or to compensate for line losses and thus maintain the current through the rotor winding 3.

[0035] For this purpose, alternating current is applied to the primary coil 29 on the stator side via a power supply device 28. In this example, the power supply device 28 is formed by a converter 36, which, or its semiconductor switch (not shown), is controlled by a control device 32 in the first operating mode so that the converter 36 operates as an inverter, inverting the direct current supplied by the DC on-board power grid 35. Thus, alternating current is generated in the primary coil 29, thereby generating an alternating electromagnetic field in the region of the secondary coil 5, thereby inducing an alternating voltage in the secondary coil 5.

[0036] In the first operating mode, the induced AC voltage is then rectified using the rotor-side converter circuit 4, thus applying a DC voltage to the rotor coil 3 and thereby increasing or maintaining the current flowing through the rotor coil 3. Similarly, the rotor-side converter circuit 4 can be controlled accordingly by the control device 32. For this purpose, in particular, the control signal from the control device 32 can be transmitted to the rotor 1 in a contactless manner, for example, through another pair of primary and secondary coils (not shown). Alternatively, for example, a separate rotor-side control device can be provided, or the control signal can be transmitted via at least one slip ring.

[0037] The following reference is made to the second operating mode via the rotor-side converter circuit 4. Figure 2In more detail, the converter circuit can also be used to actively eliminate the rotor magnetic field of the rotor winding 3 and guide the recovered energy back to the power supply unit 28 and then to the DC vehicle power grid 35. Thus, the recovered energy can be used, for example, to charge the battery 37, or to power another DC component 38 in the DC vehicle power grid 35. In this case, the stator-side converter 36 operates as a rectifier to rectify the AC voltage induced in the primary coil 29 through inductive energy transfer.

[0038] exist Figure 2 The diagram shows a detailed view of the converter circuit 4 on the rotor side. The converter circuit 4 is electrically connected to the secondary coil 5 via the first-stage coil contact 6 and the second-stage coil contact 7, and is electrically connected to the rotor winding 3 via the first rotor winding contact 8 and the second rotor winding contact 9. The first-stage coil contact 6 and the second-stage coil contact 7 are connected to the first rotor winding contact 8 via first line branches 10 and 11, and to the second rotor winding contact 9 via second line branches 12 and 13, respectively.

[0039] To both increase or maintain the current guided through rotor winding 3 and actively decrease this current, thereby actively eliminating the rotor magnetic field, converter circuit 4 is configured to provide DC voltages of different polarities to rotor winding contacts 8 and 9 in both a first operating mode and a second operating mode. In this example, in the first operating mode, to establish or maintain the rotor magnetic field, the potential applied to the first rotor winding contact 8 should be higher than the potential applied to the second rotor winding contact 9. Conversely, in the second operating mode, the potential at the second rotor winding contact 9 should be higher than the potential at the first rotor winding contact 8, in order to provide a reverse voltage for weakening the magnetic field.

[0040] To achieve this, line branches 10-13 each include a first switching device and a second switching device 14-21, which are connected in series between corresponding secondary coil contacts 6, 7 and corresponding rotor winding contacts 8, 9. Each switching device 14-21 has a semiconductor switch 22, 23, with corresponding diodes 24, 25 connected in parallel with the semiconductor switch. In order to selectively block the flow of current in two current flow directions through the corresponding line branch 10-13 or the corresponding half-bridges 30, 31 formed by the two line branches 10-13 by appropriately switching the semiconductor switches 22, 23, the conduction direction of the corresponding diode 24 of the corresponding first switching device 14-17 is opposite to the conduction direction of the corresponding diode 25 of the corresponding second switching device 18-21.

[0041] According to Figure 2In the example, diodes 24 and 25, constructed separately from the corresponding semiconductor switches 22 and 23, are used for clarity. However, it is advantageous to use semiconductor switches with body diodes instead, since separate, parallel diodes are unnecessary in this case. In particular, the corresponding semiconductor switches 22 and 23 can be MOSFETs, which include corresponding diodes 24 and 25 as body diodes 24 and 25.

[0042] In the first operating mode, the control device 32 can switch the semiconductor switches 23 of all the second switching devices 18-21 to continuous conduction and switch the semiconductor switches 22 of the first switching devices 14-17 to intermittent conduction in order to rectify the AC voltage delivered via the secondary coil connections 6, 7. Therefore, the function achieved in the first operating mode is essentially the same as that provided by a known rotor-side active rectifier, which has only one semiconductor switch for each line branch.

[0043] In the second operating mode, the control device can switch all semiconductor switches 22 of the first switching devices 14-17 to continuous conduction and switch semiconductor switches 23 of the second switching devices 18-21 to intermittent conduction, so as to convert at least a portion of the DC current guided from the first rotor winding contact 8 to the second rotor winding contact 9 via the rotor winding 3 into AC current supplied to the secondary coil 5. Because the diodes 25 of the intermittently switched semiconductor switches 23 in the corresponding half-bridges block the current flowing from the second rotor winding contact 9 to the first rotor winding contact 8 through the half-bridges 30 and 31, the current direction can be achieved in the second operating mode such that the potential at the second rotor winding contact 9 is more positive than the potential at the first rotor winding contact 8, thereby reducing the current flowing from the first rotor winding contact 8 to the second rotor winding contact 9 through the rotor winding 3, which generates the rotor magnetic field. Thus, energy is directed from the rotor winding 3 via the secondary coil 5 and the primary coil 29 to the power supply unit 28 and then via the power supply unit to the DC vehicle power grid 35.

[0044] During normal operation of the vehicle 33, the synchronous motor 2 operates in a first operating mode in this example to establish or maintain the rotor magnetic field and thus provide torque. It switches to a second operating mode only when triggering conditions are met.

[0045] In this example, the triggering condition is met under the following circumstances: for example, when the vehicle stops or when driving torque is not expected to be needed for a long period of time, the synchronous motor 2 is deactivated. On the other hand, the triggering condition is met under the following circumstances: for example, when an accident involving the vehicle 33 is detected by means of the collision sensor 39 or when other safety systems, such as airbags and / or seat belt tensioners, are triggered.

[0046] In an extended version of the illustrated example, the triggering condition may also be met in other circumstances, such as when the synchronous motor 2 changes from a high-power mode to a mode in which the synchronous motor provides less power, for example, when the vehicle 33 is operating in an energy-saving mode or when the state of charge of the battery 37 is low.

Claims

1. A rotor for a separately excited synchronous machine (2), the rotor comprising a rotor winding (3), a current transformer circuit (4) and a secondary coil (5), wherein, The converter circuit (4) comprises: a first secondary winding contact (6) and a second secondary winding contact (7), which are electrically connected to the secondary winding (5), a first rotor winding contact (8) and a second rotor winding contact (9), which are electrically connected to the rotor winding (3), the converter circuit is designed to convert, in the first operating mode, an alternating voltage induced in the secondary winding (5) and delivered via the secondary winding connection (6, 7) into a direct voltage in order to load the rotor winding (3) via the rotor winding connection (8, 9) with a direct voltage in order to establish and / or maintain the rotor field, wherein the first secondary winding contact (6) and the second secondary winding contact (7) are connected to the first rotor winding contact (8) via a first line branch (10, 11) and to the second rotor winding contact (9) via a second line branch (12, 13), respectively, characterized in that the respective first and second line branches (10-13) comprise a first and a second switching device (14-21) which are connected in series with one another between the respective secondary winding contact (6, 7) and the respective rotor winding contact (8, 9), wherein the switching devices (14-21) each have a semiconductor switch (22, 23) which comprises a body diode (24, 25) and / or to which a diode (24, 25) is connected in parallel, wherein the diodes (24) of the first switching devices (14-17) and the diodes (25) of the second switching devices (18-21) of the respective line branch (10-13) have mutually opposite conduction directions.

2. The rotor according to claim 1, characterized in that the respective semiconductor switch (22, 23) is a MOSFET which comprises a body diode (24, 25).

3. A separately excited synchronous machine, characterized in that the separately excited synchronous machine comprises a rotor (1) according to claim 1 or 2, wherein the rotor (1) is rotatably supported on a stator (26), wherein the synchronous machine (2) comprises a supply device (28) which is designed to load an alternating voltage to a primary winding (29) of the stator (26), as a result of which an alternating voltage is induced in the secondary winding (29) of the rotor (1).

4. The separately excited synchronous machine according to claim 3, characterized in that A respective line branch pair comprising one of the first line branches (10, 11) and one of the second line branches (12, 13) forms a respective half bridge (30, 31) between the first rotor winding contact (8) and the second rotor winding contact (9), wherein the conducting direction of the diodes (24) of the first switching devices (14-17) in the respective half bridge (30, 31) points from the second rotor winding contact (9) to the first rotor winding contact (8), wherein the synchronous machine (2) comprises a control device (32) which is designed to switch the semiconductor switches (23) of all second switching devices (18-21) permanently on and to switch the semiconductor switches (22) of the first switching devices (14-17) intermittently on in a first operating mode in order to rectify an alternating voltage which is delivered via the secondary winding connections (6, 7).

5. The separately excited synchronous machine according to claim 4, characterized in that the control device is designed to switch the semiconductor switches (22) of all first switching devices (14-17) permanently on and to switch the semiconductor switches (23) of the second switching devices (18-21) intermittently on in a second operating mode in order to convert at least a portion of a direct current which is conducted via the rotor winding (3) from the first rotor winding contact (8) to the second rotor winding contact (9) into an alternating current which is delivered to the secondary winding (5) in order to guide energy from the rotor winding (3) via the secondary winding (5) and the primary winding (29) to the power supply device (28) or to a further component of the separately excited synchronous machine (2).

6. A motor vehicle, characterized in that the motor vehicle comprises a separately excited synchronous machine (2) according to any one of claims 3 to 5.

7. The motor vehicle according to claim 6, characterized in that in at least one operating state of the motor vehicle (33), the synchronous machine (2) is mechanically coupled to at least one wheel (34) of the motor vehicle (33) in such a way that the synchronous machine (2) drives the wheel (34) as a power device.

8. The motor vehicle according to claim 6 or 7, characterized in that the motor vehicle (33) comprises a direct current on-board power supply network (35), wherein the control device (32) or a control device is designed to operate a power supply device (28) which is designed as a converter (36) as an inverter in a first operating mode in order to inductively transfer energy to the rotor (1) and as a rectifier in a second operating mode in which the rotor field of the rotor winding (3) is actively eliminated in order to rectify an alternating voltage which is induced in the primary winding (29) and thereby to feed energy into the direct current on-board power supply network (35).

9. The motor vehicle according to claim 8, characterized in that The control device (32) is designed to change from the first operating mode to the second operating mode in order to actively eliminate the rotor field generated by the rotor winding (3) when a triggering condition is fulfilled, wherein the fulfillment of the triggering condition depends on whether an incident is present and / or whether a shutdown process of the synchronous machine (2) is present.

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