Rotor, separately excited synchronous machine and motor vehicle

Abstract

Rotor for a separately excited synchronous machine (2), comprising a rotor winding (3), a converter circuit (4) and a secondary winding (5), wherein the converter circuit (4) comprises a first and second secondary winding contact (6, 7) and a first and second rotor winding contact (8, 9) and is configured to convert an alternating voltage induced in the secondary winding (5) into a direct voltage in a first operating mode in order to supply the rotor winding (3) with this direct voltage via the rotor winding terminals (8, 9), wherein the first and second secondary winding contacts (6, 7) are each 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), wherein the respective first and second line branches (10-13) comprise a first and a second switching means (14-21) which are connected in series with each other between the respective secondary winding contacts (6,7) and the respective rotor winding contact (8, 9) are switched, wherein the respective switching means (14-21) has a semiconductor switch (22, 23) comprising an intrinsic diode (24, 25) and / or to which a diode (24, 25) is connected in parallel, wherein the diode (24) of the first switching means (14-17) and the diode (25) of the second switching means (18-21) of the respective line branch (10-13) have opposite forward directions.

Description

[0001] The invention relates to a rotor for a separately excited synchronous machine, comprising a rotor winding, a converter circuit and a secondary coil, wherein the converter circuit comprises a first and second secondary coil contact which are electrically connected to the secondary coil, and a first and second rotor winding contact which are electrically connected to the rotor winding and is configured to convert an alternating voltage induced in the secondary coil and supplied via the secondary coil terminals into a direct voltage in a first operating mode, in order to supply the rotor winding with this direct voltage via the rotor winding terminals for the purpose of establishing and / or maintaining the rotor magnetic field, wherein the first and second secondary coil contact are each 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 addition, the invention relates to a separately excited synchronous machine and a motor vehicle.

[0002] Externally excited synchronous machines, unlike permanent magnet synchronous machines, do not use magnetic materials in the rotor. They generate the rotor magnetic field by energizing a rotor winding. This results in additional degrees of freedom in the control and design of the electric machine, leading to improvements in efficiency and performance. This can be particularly relevant when the electric machine is intended to power a motor vehicle, as in this case, high power output with low weight and compact design is often required.

[0003] According to current technology, the rotor winding is energized either via slip ring contacts or contactlessly via a power transmission system with an inductive rotary transformer. In the latter case, a stator-side inverter, an inductive rotary transformer comprising a stator-side primary coil and a rotor-side secondary coil, a rotor-side rectifier, and optionally a filter for smoothing the excitation current are typically used to energize the rotor winding.

[0004] For efficiency reasons, it is often advantageous to set a high rotor magnetic field by means of high excitation currents, since with increasing rotor magnetic field lower alternating currents are required in the stator coils to achieve the same torques of the synchronous machine.

[0005] Due to the typically high inductance of the rotor winding and the preferably high excitation current used, large amounts of energy accumulate in the rotor during operation. It is therefore advantageous to implement a "rapid de-energizing" mechanism for the rotor winding in certain operating situations, such as in the event of an accident. However, this requires additional circuitry on the rotor side for energy dissipation.

[0006] The invention is therefore based on the objective of providing an improved externally excited synchronous machine, or an improved rotor for such a synchronous machine, in contrast, particularly with regard to a targeted reduction of the rotor magnetic field.

[0007] The task is accomplished by a rotor of the type mentioned above, wherein the respective first and second conduction branch comprises a first and a second switching means which are connected in series with each other between the respective secondary coil contact and the respective rotor winding contact, wherein the respective switching means has a semiconductor switch which includes an intrinsic diode and / or to which a diode is connected in parallel, wherein the diode of the first switching means and the diode of the second switching means of the respective conduction branch have opposite forward directions to each other.

[0008] If both semiconductor switches of a circuit branch are reverse-biased, current flow through the branch is blocked in both directions. Conversely, if both semiconductor switches are conducting, current flow through the branch is possible in both directions, particularly with low resistance. In switching states where only one of the semiconductor switches of the respective circuit path is reverse-biased, the diode connected in parallel or intrinsically linked to this diode allows current flow through the power branch only in the forward direction of this diode.

[0009] The inventive design allows the power converter circuit to be used not only to receive energy via the secondary coil for building up the rotor magnetic field in the first operating mode, but also in a second operating mode to actively reduce the rotor magnetic field of the rotor winding and radiate the energy extracted from the rotor magnetic field via the secondary coil or transfer it to the stator-side primary coil. This enables a rapid reduction of the rotor magnetic field and thus a rapid reduction of the current flowing through the rotor winding, which can be advantageous, for example, in accident situations, without requiring a special rotor-side protection circuit, such as a clamping network.On the other hand, the return transfer of energy to a stator-side primary coil enabled the recuperation of the energy used to build up the rotor magnetic field, thereby increasing the efficiency of a synchronous machine encompassing this rotor.

[0010] In contrast to the design according to the invention, conventional active rectifiers for supplying current to a rotor winding use only a single semiconductor switch with an intrinsic or parallel-connected diode in the respective line branch. When the rotor winding is energized to build up or maintain the rotor magnetic field, this diode is subjected to a reverse voltage. However, if active field decay is desired in such a design to achieve particularly rapid field decay and / or recuperation, the rotor winding, and thus also the diode, would have to be subjected to a reverse voltage.However, once the diode reaches its freewheeling voltage, it carries current at a low resistance, so that when using a conventional rotor-side converter, only very low voltages below this freewheeling voltage can be used to actively reduce the current through the rotor winding.

[0011] By using series-connected semiconductor switches with parallel-connected or intrinsic diodes with opposite forward direction according to the invention, this problem is avoided, since in this case, as already explained above, forward or free-running can be controlled separately for the individual current directions.

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

[0013] The semiconductor switch in question can be a MOSFET, which includes the intrinsic diode. A metal-oxide-semiconductor field-effect transistor (MOSFET) is a transistor with an insulated gate and is therefore well-suited for switching high currents or voltages. The presence of an intrinsic diode eliminates the need for a separate freewheeling diode, preventing voltage spikes when switching high inductor currents. MOSFETs also enable short switching times, thus minimizing switching losses, which is particularly relevant in power converters that typically require high-frequency switching of the semiconductor switches.

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

[0015] The power supply device can in particular be an inverter which is supplied by a DC voltage source, for example a battery, which can in particular be arranged outside the synchronous machine, i.e. for example in a motor vehicle comprising the synchronous machine.

[0016] Each pair consisting of one of the first conductor branches and one of the second conductor branches can form a half-bridge between the first and second rotor winding contacts, wherein the forward direction of the diodes of the first switching devices in the respective half-bridge is directed from the second rotor winding contact to the first rotor winding contact. The synchronous machine can include a control device configured to continuously switch the semiconductor switches of all second switching devices and intermittently switch the semiconductor switches of the first switching devices in order to rectify the alternating voltage supplied via the secondary coil terminals. Intermittent switching, as used here, means alternating conducting and blocking, particularly with a periodic switching pattern.

[0017] Since the forward directions of the first and second switching devices are opposite to each other, the forward direction of the diodes of the second switching devices in the respective half-bridge in the above case is directed from the first to the second rotor winding contact.

[0018] In the first operating mode, the converter circuit can thus provide a more positive potential at the first rotor winding contact compared to the potential at the second rotor winding contact, thereby increasing the current flow through the rotor winding from the first to the second rotor winding contact and compensating for line losses. The direction of current flow is considered to be the conventional current direction here, as well as in the preceding and following descriptions.

[0019] The control device can also be configured to continuously switch the semiconductor switches of all first switching devices and intermittently switch the semiconductor switches of the second switching devices in a second operating mode, in order to convert at least part of a direct current carried through the rotor winding from the first rotor winding contact to the second rotor winding contact into an alternating current supplied to the secondary coil, in order to carry energy from the rotor winding via the secondary coil and the primary coil to the current supply device or another component of the separately excited synchronous machine.

[0020] During energy transfer from the rotor winding back to the stator, the current flowing through the rotor winding is actively reduced. To achieve this, starting from the current flow caused or maintained by the first operating mode, the potential at the second rotor winding contact should be more positive than the potential at the first rotor winding contact. Since the diodes connected in parallel to the semiconductor switches that are intermittently switched in the second operating mode block current flow in the conventional direction from the second rotor winding contact to the first rotor winding contact through the respective half-bridge when these semiconductors are switched off, the inverter circuit can provide high counter-potentials, thus rapidly reducing or recuperating the current in the rotor winding.

[0021] The invention also relates to a motor vehicle comprising a separately excited synchronous machine according to the invention. As already explained at the outset, high power densities for electrical machines are frequently required in motor vehicles, making the additional degrees of freedom in machine design through the use of a separately excited synchronous machine particularly advantageous. Since high rotor magnetic field strengths can also be advantageous in this context, the rapid reduction of rotor winding currents made possible by the inventive design of the rotor or the synchronous machine is particularly relevant.

[0022] The synchronous motor can be mechanically coupled to at least one wheel of the vehicle in at least one operating state, such that the synchronous motor drives the wheel as a drive motor. The respective wheel can be permanently coupled to the synchronous motor, for example, in the case of individual wheel drive. However, it is also possible for the synchronous motor to drive several wheels of the vehicle via a transmission and / or a differential, or to be decoupled from them.

[0023] The motor vehicle may include a DC electrical system, wherein the control device is configured to operate the power supply unit, designed as a further power converter, as an inverter in the first operating mode to inductively transfer energy to the rotor, and in the second operating mode, in which the rotor magnetic field of the rotor winding is actively reduced, as a rectifier to rectify an alternating voltage induced in the primary coil and thereby feed energy into the DC electrical system.

[0024] In particular, in the second operating mode, the energy recovered during the reduction of the rotor magnetic field can be used to charge a battery in the DC electrical system and / or to operate another component located there.

[0025] In particular, the control unit can control the rotor-side converter circuit or its semiconductor switches in the second operating mode, as explained above, to actively reduce the rotor current. If the control unit is part of the stator or generally located outside the rotor, control signals for the rotor-side converter circuit can be transmitted inductively. The semiconductor switches of the rotor-side converter circuit and / or semiconductor switches of the stator-side converter can be controlled via a galvanically isolated gate driver.

[0026] The control device can be configured to switch from the first to the second operating mode when a tripping condition is met, in order to actively reduce the rotor magnetic field generated by the rotor winding. Preferably, the fulfillment of the tripping condition can depend on whether an accident and / or a shutdown of the synchronous machine has occurred.

[0027] An accident can be detected, for example, by collision sensors or when a distance threshold, measured by distance sensors, is breached. A signal indicating an accident can also be provided by other vehicle systems, such as safety systems like an airbag control unit, a seatbelt pretensioner, or similar components. In the event of an accident, components carrying potentially high voltages should be de-energized quickly. For coils with high inductance, such as the rotor winding, active de-energization of the coil is advantageous, as enabled by the inventive design of the rotor, the synchronous machine, or the vehicle.

[0028] When the synchronous machine is switched off, the rotor magnetic field should typically be reduced to zero, which is why active coil current reduction, especially in conjunction with energy recuperation from the rotor magnetic field, is particularly advantageous in this case.

[0029] Further advantages and details of the invention will become apparent from the following exemplary embodiments and the accompanying drawings. These schematically illustrate: Fig. 1 a detailed view of an embodiment of the motor vehicle according to the invention, comprising an embodiment of the synchronous machine according to the invention, which in turn comprises an embodiment of the rotor according to the invention, and Fig. 2 a detailed view of the rotor according to Fig. 1 used power converter circuit.

[0030] Fig. Figure 1 shows a detailed view of a motor vehicle 33, in which one of the wheels 34 of the motor vehicle 33 and a separately excited synchronous machine 2 assigned to the wheel 34 as a drive motor are shown. The direct coupling of the rotor 1 of the synchronous machine 2 to the wheel 34 shown is purely exemplary. Alternatively, the synchronous machine 2 could drive the wheel 34 or even several wheels, for example via a gearbox and / or a differential.

[0031] The synchronous machine 2 is powered by a DC electrical system 35 of the motor vehicle 33, which includes a battery 37 and other DC components 38. For clarity, in Fig. Figure 1 shows only that part of the motor electronics which serves to supply current to the rotor winding 3. The intermittent supply of current to the stator coils 40 for applying torque to the rotor about the axis of rotation 27 can be achieved, for example, by the stator-side converter 36 or by a separate converter not shown.

[0032] In a first operating mode of the synchronous machine 2, energy is transferred contactlessly from the stator 26 to the rotor 1 in order to increase the rotor magnetic field by increasing the current carried through the rotor winding 3 or to compensate for line losses and thus maintain the current through the rotor winding 3.

[0033] For this purpose, the stator-side primary coil 29 is supplied with an alternating current by the power supply unit 28. In this example, the power supply unit 28 is formed by a power converter 36, which, or rather its semiconductor switches (not shown), is controlled in the first operating mode by the control unit 32 to operate the power converter 36 as an inverter that converts the direct current supplied by the DC electrical system 35. This results in an alternating current in the primary coil 29, which in turn creates an alternating electromagnetic field in the area of ​​the secondary coil 5, thereby inducing an alternating voltage in the secondary coil 5.

[0034] In the first operating mode, a rotor-side converter circuit 4 is used to rectify the induced AC voltage and thus apply a DC voltage to the rotor coil 3, thereby increasing or maintaining the current flowing through the rotor coil 3. The corresponding control of the rotor-side converter circuit 4 can also be carried out by the control unit 32. For this purpose, control signals from the control unit 32 can be transmitted contactlessly to the rotor 1, for example, via another pair (not shown) consisting of a primary and a secondary coil. Alternatively, a separate rotor-side control unit could be provided, or the control signals could be transmitted via at least one slip ring.

[0035] Through a following discussion with reference to Fig. In a second operating mode, as further explained in section 2, the rotor-side converter circuit 4 can also be used to actively reduce the rotor magnetic field of the rotor winding 3 and to feed the recovered energy back to the power supply unit 28 and via this unit into the DC electrical system 35. Thus, the recovered energy can, for example, be used to charge the battery 37 or to operate another DC component 38 in the DC electrical system 35. In this case, the stator-side converter 36 is operated as a rectifier to rectify the AC voltage induced in the primary coil 29 by the inductive energy transfer.

[0036] A detailed view of the rotor-side power converter circuit 4 is shown in Fig. Figure 2 shows the power converter circuit 4. The converter circuit is electrically connected to the secondary coil 5 via a first and second secondary coil contact 6, 7 and to the rotor winding 3 via a first and second rotor winding contact 8, 9. The first and second secondary coil contacts 6, 7 are each connected to the first rotor winding contact 8 via a first branch 10, 11 and to the second rotor winding contact 9 via a second branch 12, 13.

[0037] To enable both an increase or maintenance of the current flowing through the rotor winding 3 and an active reduction of this current, thus actively reducing the rotor magnetic field, the converter circuit 4 is configured to provide DC voltages with opposite polarities at the rotor winding contacts 8 and 9 in the first and second operating modes. In the first operating mode, a higher potential is applied to the first rotor winding contact 8 than to the second rotor winding contact 9 to build up or maintain the rotor magnetic field. In the second operating mode, however, the potential at the second rotor winding contact 9 is higher than the potential at the first rotor winding contact 8 to provide a counter-voltage for field reduction.

[0038] To enable this, the conductor branches 10-13 each comprise a first and a second switching element 14-21, which are connected in series with each other between the respective secondary coil contacts 6, 7 and the respective rotor winding contacts 8, 9. Each switching element 14-21 has a semiconductor switch 22, 23, to which a respective diode 24, 25 is connected in parallel. In order to enable selective blocking of the current flow in both directions through the respective conductor branch 10-13 or through the respective half-bridge 30, 31 formed by two conductor branches 10-13 by appropriately switching the semiconductor switches 22, 23, the respective diode 24 of the respective first switching element 14-21 has a forward direction that is opposite to the forward direction of the respective diode 25 of the respective second switching element 18-21.

[0039] In the example according to Fig.For clarity, diodes 24 and 25 are used in Figure 2, which are separate from the respective semiconductor switches 22 and 23. However, it may be advantageous to use semiconductor switches with an intrinsic diode instead, since in this case a separate, parallel-split diode is not necessary. In particular, the respective semiconductor switch 22 and 23 can be a MOSFET that incorporates the respective diode 24 and 25 as its intrinsic diode.

[0040] In the first operating mode, the control unit 32 can continuously switch the semiconductor switches 23 of all secondary switching devices 18-21 and intermittently switch the semiconductor switches 22 of the first switching devices 14-17 in order to rectify the alternating voltage supplied via the secondary coil terminals 6, 7. In the first operating mode, this results in essentially the same function as that provided by known rotor-side active rectifiers, which have only a single semiconductor switch per line branch.

[0041] In the second operating mode, the control device can continuously switch the semiconductor switches 22 of all first switching devices 14-17 and intermittently switch the semiconductor switches 23 of the second switching devices 18-21 in order to convert at least part of a direct current carried through the rotor winding 3 from the first rotor winding contact 8 to the second rotor winding contact 9 into an alternating current supplied to the secondary coil 5.Since the diodes 25 of the semiconductor switches 23, which are intermittently switched in the second operating mode, block current flow from the second rotor winding contact 9 to the first rotor winding contact 8 via the half-bridge 30, 31 in the respective half-bridge, the current direction in the second operating mode can be such that the potential at the second rotor winding contact 9 is more positive than the potential at the first rotor winding contact 8. This reduces the current flow 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. As a result, energy is transferred from the rotor winding 3 via the secondary coil 5 and the primary coil 29 to the current supply device 28 and from there into the DC network 35.

[0042] During normal operation of the vehicle 33, the synchronous machine 2 in this example operates in the first operating mode to build up and maintain the rotor magnetic field, thus enabling torque generation by the synchronous machine 2. A switch to the second operating mode only occurs when a trigger condition is met.

[0043] The triggering condition is met in the example on the one hand when the synchronous machine 2 is deactivated, for example when the vehicle is switched off or when no drive torque is expected to be required for an extended period of time. On the other hand, the triggering condition is met when an accident involving the vehicle 33 is detected, for example by means of a collision sensor 39, or when other safety systems, such as an airbag and / or a seatbelt pretensioner, are triggered.

[0044] Extending the example described, the triggering condition could also be met in other cases, for example when the synchronous machine 2 switches from a high-performance mode to a mode in which it provides lower power, for example for operating the motor vehicle 33 in an economy mode or when the battery 37 has a low charge level.

Claims

[1] Rotor for a separately excited synchronous machine (2), comprising a rotor winding (3), a converter circuit (4) and a secondary coil (5), wherein the converter circuit (4) comprises a first and second secondary coil contact (6, 7) electrically connected to the secondary coil (5) and a first and second rotor winding contact (8, 9) electrically connected to the rotor winding (3) and is configured to convert, in a first operating mode, an alternating voltage induced in the secondary coil (5) and supplied via the secondary coil terminals (6, 7) into a direct voltage in order to supply the rotor winding (3) via the rotor winding terminals (8, 9) with this direct voltage for the purpose of establishing and / or maintaining the rotor magnetic field, wherein the first and second secondary coil contact (6, 7) are each connected to the first rotor winding contact (8) via a first line branch (10, 11) and to the second line branch (12, 11) via a second line branch (12, 11)13) are connected to the second rotor winding contact (9), , characterized by , that the respective first and second conduction branch (10-13) comprise a first and a second switching means (14-21) which are connected in series with each other between the respective secondary coil contact (6, 7) and the respective rotor winding contact (8, 9), wherein the respective switching means (14-21) has a semiconductor switch (22, 23) which includes an intrinsic diode (24, 25) and / or to which a diode (24, 25) is connected in parallel, wherein the diode (24) of the first switching means (14-17) and the diode (25) of the second switching means (18-21) of the respective conduction branch (10-13) have opposite forward directions to each other. [2] Rotor according to claim 1, characterized by , that the respective semiconductor switch (22, 23) is a MOSFET comprising the intrinsic diode (24, 25). [3] Externally excited synchronous machine, characterized by, that it comprises the rotor (1) according to claim 1 or 2, wherein the rotor (1) is rotatably mounted on a stator (26), wherein the synchronous machine (2) comprises a current supply device (28) which is configured to supply an alternating current to a primary coil (29) of the stator (26), thereby inducing the alternating voltage in the secondary coil (29) of the rotor (1). [4] Externally excited synchronous machine according to claim 3, characterized by, that each pair consisting of one of the first conductor branches (10, 11) and one of the second conductor branches (12, 13) forms a respective half-bridge (30, 31) between the first and the second rotor winding contact (8, 9), wherein the forward direction of the diodes (24) of the first switching means (14-17) in the respective half-bridge (30, 31) is directed 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 configured to continuously switch the semiconductor switches (23) of all second switching means (18-21) in the first operating mode and to intermittently switch the semiconductor switches (22) of the first switching means (14-17) in order to rectify the alternating voltage supplied via the secondary coil terminals (6, 7). [5] Externally excited synchronous machine according to claim 4, characterized by, that the control device is configured to continuously switch the semiconductor switches (22) of all first switching means (14-17) and intermittently switch the semiconductor switches (23) of the second switching means (18-21) in a second operating mode, in order to convert at least part of a direct current carried through the rotor winding (3) from the first rotor winding contact (8) to the second rotor winding contact (9) into an alternating current supplied to the secondary coil (5) in order to carry energy from the rotor winding (3) via the secondary coil (5) and the primary coil (29) to the current supply device (28) or another component of the separately excited synchronous machine (2). [6] motor vehicle, characterized by , that it comprises a separately excited synchronous machine (2) according to one of claims 3 to 5. [7] Motor vehicle according to claim 6, characterized by, that the synchronous machine (2) is mechanically coupled to at least one wheel (34) of the motor vehicle (33) in at least one operating state of the motor vehicle (33) such that the synchronous machine (2) drives the wheel (34) as a drive motor. [8] Motor vehicle according to claim 6 or 7, characterized by , that the motor vehicle (33) comprises a DC electrical system (35), wherein the or a control device (32) is configured to operate the current supply device (28) designed as a current converter (36) as an inverter in the first operating mode to inductively transfer energy to the rotor (1), and in the or a second operating mode in which the rotor magnetic field of the rotor winding (3) is actively reduced, as a rectifier to rectify an alternating voltage induced in the primary coil (29) and thereby feed energy into the DC electrical system (35). [9] Motor vehicle according to claim 8, characterized by, that the control device (32) is configured to switch from the first to the second operating mode when a tripping condition is met, in order to actively reduce the rotor magnetic field generated by the rotor winding (3), wherein the fulfillment of the tripping condition depends on whether an accident and / or a shutdown process of the synchronous machine (2) has occurred.

Images