Externally excited synchronous machine and motor vehicle

Abstract

Externally excited synchronous machine with a stator (2) and a rotor (3) rotatably mounted on the stator (2), wherein the rotor (3) comprises a rotor winding (4) for providing a rotor magnetic field when the rotor winding (4) is energized, an active power converter (5) for energizing the rotor winding (4) and control electronics (6) for controlling the power converter (5), characterized in that the rotor (2) has an internal power supply means (7) which is electrically connected to both ends of the rotor winding (4) and is configured to reduce a rotor winding current flowing through the rotor winding (4), at least in a fallback operating mode of the synchronous machine (1), in order to energize the control electronics (6) via an operating voltage input (8) of the control electronics (6).

Description

[0001] The invention relates to a separately excited synchronous machine with a stator and a rotor rotatably mounted on the stator, wherein the rotor comprises a rotor winding for providing a rotor magnetic field when the rotor winding is energized, an active power converter for energizing the rotor winding, and control electronics for controlling the power converter. The invention also relates to 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. Such an inductive power transmission system to the rotor is disclosed, for example, in German patent application DE 10 2017 214 776 A1. With inductive power transmission, it is advantageous to use an active converter on the rotor side to minimize rectification losses.

[0004] The generic publication DE 10 2014 224 701 A1 discloses a device with an inductive coupler for the bidirectional transmission of energy and data between a primary winding of the inductive coupler and a secondary winding of the inductive coupler inductively coupled to the primary winding. The device can be used in an electrically excited synchronous machine to supply energy to a rotatable excitation winding.

[0005] A synchronous machine in which an inductive supply of electrical energy to the respective rotor coil is used is also known from publication DE 10 2021 212 549 A1.

[0006] When using an active converter to power the rotor winding, a failure or malfunction of stator-side components can lead to the converter's control electronics no longer receiving power. This can result in the gate drivers of the converter's semiconductor switches being de-energized. This can lead to an undefined state of the rotor-side converter, potentially causing, for example, an unplanned short circuit of the rotor winding or a very low-impedance freewheeling condition. This is particularly problematic in the event of an accident, as a rapid reduction of current flow is typically required in such cases. Another example of an undesirable state that can potentially occur with de-energized control electronics is the application of an intermediate voltage to at least one of the semiconductor switches, leading to a conductive state with high resistance.In this case, the energy of the rotor field is dissipated via the appropriately set semiconductor switch(es), which can result in high waste heat and thus strong heating and potentially damage to the respective semiconductor switch.

[0007] The invention is therefore based on the objective of providing an improved externally excited synchronous machine in which, in particular, the effect of a failure of stator-side components can be reduced.

[0008] The object is achieved according to the invention by a separately excited synchronous machine of the type mentioned above, wherein the rotor has a rotor-internal energy supply means which is electrically connected to both ends of the rotor winding and is configured to reduce a rotor winding current flowing through the rotor winding, at least in a fallback operating mode of the synchronous machine, in order to power the control electronics via an operating voltage input of the control electronics.

[0009] The rotor's internal power supply can ensure a current supply to the control electronics in all rotor operating states where a sufficient rotor winding current flows. This allows the converter to be controlled by the control electronics in these operating states, independent of potential defects and / or malfunctions of stator-side components or, more generally, of components external to the rotor. The design according to the invention particularly helps to reliably avoid undefined switching states of semiconductor switches in the converter.

[0010] It was recognized that the aforementioned problems, which can result from undefined states of the power converter, are primarily problematic in operating situations where a rotor field is present and thus current is flowing through the rotor winding. Therefore, the design of the rotor according to the invention, or of a separately excited synchronous machine encompassing it, can significantly reduce the negative effects of stator-side faults or defects.

[0011] The power supply can be connected directly or via at least one other electronic component to the respective end of the rotor winding. Thus, the power supply is connected in parallel to the coil and, in particular, to a circuit section connected to the coil that forms a freewheel for the coil. A portion of the current that would otherwise be supplied to the coil can therefore be diverted, at least in fallback mode, and used instead, especially after suitable voltage regulation or stabilization, to power the control electronics.

[0012] If the freewheeling circuit includes at least one diode, then when current flows through the coil and the freewheeling circuit, at least the diode's forward voltage, which can be approximately 0.2 V to 0.4 V, is present across the diode and thus across the coil. The power supply can then be, in particular, a power converter, especially a DC / DC converter, which can convert the aforementioned voltage drop into the desired operating voltage for the control electronics.

[0013] A freewheeling circuit across at least one diode results, for example, if the freewheeling circuit is formed by the converter and uses this semiconductor switch with parallel-connected or intrinsic diodes for current direction, and if at least one semiconductor switch of the respective half-bridge is closed.

[0014] Regardless of the specific design of the freewheel, a lower limit for the voltage drop across the rotor winding results due to the ohmic resistance of the rotor winding, so that the above-explained approach to current supply can be used even with a very low resistance freewheel of the rotor winding, for example if all semiconductor switches of the converter are temporarily open.

[0015] The synchronous machine may additionally have a stator-side power supply means which is connected to the control electronics via a power transmission means designed to transmit electrical energy from the stator to the rotor and is designed to power the control electronics at least in a normal operating mode of the synchronous machine.

[0016] Using a stator-side power supply to power the rotor-side control electronics is advantageous because the rotor's internal power supply can only energize the control unit once sufficient current is flowing through the rotor winding and a certain rotor field has been established. While it would theoretically be possible, through suitable circuit design, for the active converter to act as a passive converter for the initial energizing of the rotor winding during inductive energy transfer from the stator to the rotor when the control electronics are de-energized (e.g., by closing all semiconductor switches), and active rectification could then only occur once a predetermined minimum current through the rotor winding or a predetermined rotor field has been reached, this is not the preferred approach.However, this would result in additional losses during the construction of the specified rotor field, which is why it is advisable to also use the stator-side power supply.

[0017] It is particularly possible that the rotor-internal energy supply is only intended as a fallback solution in case not enough energy is transferred via the energy transmission means to operate the control electronics, for example because the energy transmission means and / or the stator-side energy supply means and / or a component upstream of it, for example in the vehicle electrical system of a motor vehicle containing the synchronous machine, malfunction or fail.

[0018] The power supply means can be, for example, a battery or a connection to a DC power grid. However, it can also be, for example, a converter, or include one that converts a DC voltage supplied by the DC power grid into an AC voltage. The power transmission means can, in particular, be an inductive power transmission means with a stator-side primary coil, a rotor-side secondary coil, and, in particular, a rotor-side rectifier for rectifying the AC voltage supplied by the secondary coil. Alternatively, sliding contacts, for example, can be used as the power transmission means.

[0019] The stator-side power supply can also be combined with a power converter to provide currents for the stator coils. For example, such a power converter can provide not only alternating currents for the various phase windings of the stator, but also an excitation current, which is inductively transferred to the rotor, and an operating current for the control electronics.

[0020] A DC voltage connection of the power transmission device can be connected to the operating voltage input of the control electronics via a first diode.

[0021] The first diode prevents current supplied by the rotor's internal power supply from flowing to the power transmission medium for the control electronics. This allows, for example, the control electronics to continue receiving power even if a short circuit occurs in the power transmission medium.

[0022] The rotor-internal power supply means can be a voltage regulator or include a voltage regulator, wherein the voltage regulator is configured to regulate the voltage at a regulator output of the voltage regulator, which is connected to the operating voltage input of the control electronics, to a predetermined setpoint, at least when a voltage drop across the rotor winding or the magnitude of this voltage exceeds a predetermined voltage limit.

[0023] Voltage drop across the rotor winding can vary considerably. Using a voltage regulator can at least largely compensate for these variations, thus providing a stable operating voltage for the control electronics.

[0024] Regardless of whether voltage regulation is used to stabilize the operating voltage, a voltage regulator, for example when using a suitable switching regulator, also allows an operating voltage for the control electronics to be provided that is greater than the voltage drop across the rotor winding or its magnitude. As mentioned above, the voltage drop across the rotor winding can be less than 1.0 V, while for digital control electronics, for example, it is common to use operating voltages in the range of 2.0 V to 5.0 V.

[0025] The regulator output of the voltage regulator can be connected to the operating voltage input of the control electronics via a second diode.

[0026] If the operating voltage input of the control electronics is additionally connected to another power supply, for example, as explained above, via the power transmission means to the stator-side power supply, this only results in a current flow from the rotor-internal power supply to the operating voltage input if a voltage provided by the additional power supply or the power transmission means is sufficiently much smaller, namely by the gate voltage of the second diode, than the voltage at the regulator output.

[0027] Thus, the second diode allows for an automatic switch from normal operating mode, in which the control electronics are powered by the stator-side power supply, to fallback operating mode, in which the control electronics are powered by the rotor's internal power supply, if the stator-side power supply or the associated power transmission medium does not provide a sufficient operating voltage for the control device. Simultaneously, the second diode ensures an automatic switch back to normal operating mode as soon as a sufficient operating voltage for the control electronics is achieved, even without the rotor's internal power supply. This simple measure prevents the rotor winding current from being unnecessarily reduced to power the control device.

[0028] The designation of the second diode as such serves solely to distinguish it from the first diode mentioned above. The designation as a second diode does not necessarily require the presence of the first diode. It is possible for the first diode to be present while the second diode is not, or for the second diode to be present while the first diode is not, or for both the first and second diodes to be present. Regardless of whether the first and second diodes described above are present, the separately excited synchronous machine may contain additional diodes, for example, as part of the power converter and / or the voltage regulator.

[0029] The control electronics can include at least one gate driver for each semiconductor switch of the power converter, with each gate driver being energized by the rotor's internal power supply, at least in the fallback operating mode. This robustly prevents the semiconductor switch from being subjected to a gate voltage that would lead to a conductive state with high resistance for an extended period, provided sufficient current is present in the rotor winding. As explained earlier, such a state can lead to significant heating and potentially damage to the semiconductor switch when high currents are passed through it.

[0030] The control electronics can additionally include a processing unit configured to determine a specific control signal for each gate driver based on at least one input signal, with the control electronics being powered by the rotor's internal power supply, at least in the fallback operating mode. This can, for example, enable rectification of inductively transmitted alternating currents by the converter or, for example, a controlled field reduction of the rotor field in the event of an accident. In particular, the continued operation of the control electronics can prevent unwanted short circuits or an unwanted freewheeling operation.

[0031] The control signal can be specified, for example, by control electronics located on the stator side or outside the synchronous machine.

[0032] Alternatively or additionally, a respective sensor of the control electronics can be configured to provide the control signal or at least one of the control signals, whereby the respective sensor is powered by the rotor's internal power supply at least in the fallback operating mode.

[0033] Such a sensor can, for example, detect currents or voltages on the AC side of the converter to ensure continued rectification even if stator-side control signals are lost or not used. Alternatively or additionally, a sensor, such as an accelerometer, can be used to detect a vehicle accident and, if so, initiate a rapid shutdown of the rotor field.

[0034] In addition to the separately excited synchronous machine according to the invention, the invention relates to a motor vehicle comprising a separately excited synchronous machine according to the invention.

[0035] The stator-side power supply can, for example, be a connection or include a connection that is connected to the vehicle's DC electrical system. In vehicles with a high-voltage electrical system, this connection can be directly connected to the high-voltage system and also to a separate low-voltage system of the vehicle.

[0036] The synchronous machine can be mechanically coupled to at least one wheel of the motor vehicle in at least one operating state such that the synchronous machine drives the wheel as a drive motor. When used as a drive motor in a motor vehicle, particularly high power densities are typically desired, which is why high rotor winding currents are preferably also used in the rotor winding. As already explained above, the inventive design of the separately excited synchronous machine is particularly relevant in this case.

[0037] 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 a motor vehicle according to the invention, comprising an embodiment of a separately excited synchronous machine according to the invention, and Fig. 2 a schematic representation of relevant electronic component groups of the in Fig. 1 used externally excited synchronous machine.

[0038] Fig. Figure 1 shows a detailed view of a motor vehicle 20, which includes a separately excited synchronous machine 1, which in the example is mechanically coupled to the wheel 21 of the motor vehicle 20 and serves as a drive motor for this wheel 21.

[0039] The synchronous machine 1 comprises a stator 2 and a rotor 3 rotatably mounted on the stator 2. The rotor 3 has a rotor winding 4, the energizing of which generates a rotor magnetic field during operation of the synchronous machine 1. The rotor magnetic field interacts with an alternating field from stator coils 26 to impart a torque to the rotor 3.

[0040] The rotor winding 4 is energized as described below with additional reference to Fig. 2 will be explained in detail, through an inductive energy transfer from the stator 2 to the rotor 3. In Fig. Line 32 separates the components arranged in the stator 2 and the rotor 3, respectively.

[0041] An inverter 30, powered by the DC electrical system 22 or by a battery 23 located therein, is used to supply alternating current to a first primary coil 24 of the stator 2. This induces an alternating voltage in a first secondary coil 25 of the rotor 3, which is rectified by an active converter 5 on the rotor side to energize the rotor winding 4.

[0042] The active power converter 5, or rather its semiconductor switches 17, are controlled by control electronics 6. In this example, the control electronics include gate drivers 16 for the individual semiconductor switches 17 and a processing unit 18. This processing unit is configured to determine a control signal for each gate driver 16 based on an input signal from a sensor 19. The sensor can, for example, measure the AC voltage drop across the first secondary coil 25 so that it can be rectified even without synchronization to the stator-side inverter 30. Alternatively, the sensor 19 could be, for example, an accelerometer that can detect a vehicle accident and, in this case, rapidly reduce the current flowing through the rotor winding 4, for example, by controlling a clamping network (not shown).

[0043] In a normal operating mode of the synchronous machine 1, the control electronics 6 are powered by a stator-side power supply 9, which is designed as an inverter and is also powered via the vehicle electrical system 22 or the battery 23. For contactless energy transfer to the rotor 3, an inductive power transfer device 10 is used in this example. This device consists of a second stator-side primary coil 27, a second rotor-side secondary coil 28, and a rectifier 29. This provides galvanic isolation between the control electronics 6 and the power supply 9. In this example, the power supply 9 is also used to power a galvanically isolated gate driver 31 for the inverter 30.

[0044] If only the previously described power supply path for the control electronics 6 were available, a malfunction or failure of a component of the power transmission means 10, the power supply means 9, or even a component of the on-board power supply 22 would result in the control electronics 6 no longer receiving power, which in this case would lead to an undefined state of the power converter 5. As already explained in the general section, this can be particularly problematic if the rotor field is already erected or if high currents are already flowing through the rotor winding 4.

[0045] Therefore, the synchronous machine 1 has an internal rotor power supply 7, which is electrically connected to both ends of the rotor winding 4 and can thus, in a fallback operating mode of the synchronous machine 1, reduce the rotor winding current flowing through the rotor winding 4 in order to power the control electronics 6 via the operating voltage input 8 of the control electronics 6. In other words, in fallback operating mode, the internal rotor power supply 7 can recover some of the energy stored in the rotor field to maintain the operation of the control electronics, for example, until the rotor current has been reduced sufficiently.

[0046] In this example, the rotor's internal power supply 7 is designed as a voltage regulator 13, which operates as a DC / DC converter to convert the voltage drop across the rotor winding 4 into an output voltage at the regulator output 14, which is regulated to a predetermined setpoint. In particular, the voltage regulator 13 can operate as a boost regulator to convert a relatively low voltage drop across the rotor winding 4 into an operating voltage for the control electronics 6 that is higher than this voltage.

[0047] To enable automatic switching between normal operating mode and fallback operating mode, the regulator output 14 of the voltage regulator 13 is connected to the operating voltage input 8 of the control electronics 6 via a diode 15. Current flow from the voltage regulator 13 to the control electronics 6, and thus a reduction in the rotor winding current, only occurs when the stator-side power supply 9 and the power transmission 10 do not provide a sufficient operating voltage for the control electronics 6 at the operating voltage input 8.

[0048] In addition, in the example another diode 12 is used between the DC voltage connection 11 of the energy transmission device 10 and the operating voltage input 8 of the control electronics 6 in order to ensure that the current supply to the control electronics 6 is protected against disturbances, for example in the event of a short circuit in the energy transmission device 10.

Claims

[1] Externally excited synchronous machine with a stator (2) and a rotor (3) rotatably mounted on the stator (2), wherein the rotor (3) comprises a rotor winding (4) for providing a rotor magnetic field when the rotor winding (4) is energized, an active power converter (5) for energizing the rotor winding (4) and control electronics (6) for controlling the power converter (5), characterized by , that the rotor (2) has a rotor-internal power supply means (7) which is electrically connected to both ends of the rotor winding (4) and is configured to reduce, at least in a fallback operating mode of the synchronous machine (1), a rotor winding current flowing through the rotor winding (4) in order to power the control electronics (6) via an operating voltage input (8) of the control electronics (6). [2] Externally excited synchronous machine according to claim 1, characterized by, that the synchronous machine (1) additionally has a stator-side power supply means (9) which is connected to the control electronics (6) via a power transmission means (10) which is designed to transmit electrical energy from the stator (2) to the rotor (3) and is designed to supply power to the control electronics (6) at least in a normal operating mode of the synchronous machine (1). [3] Externally excited synchronous machine according to claim 2, characterized by , that a DC voltage connection (11) of the power transmission means (10) is connected via a first diode (12) to the operating voltage input (8) of the control electronics (6). [4] Externally excited synchronous machine according to any of the preceding claims, characterized by, that the rotor internal power supply means (7) is a voltage regulator (13) or comprises a voltage regulator (13), wherein the voltage regulator (13) is configured to regulate the voltage at a regulator output (14) of the voltage regulator (13), which is connected to the operating voltage input (8) of the control electronics (6), to a predetermined setpoint, at least when a voltage drop across the rotor winding (4) or the magnitude of this voltage exceeds a predetermined voltage limit. [5] Externally excited synchronous machine according to claim 4, characterized by , that the regulator output (14) of the voltage regulator (13) is connected to the operating voltage input (8) of the control electronics (6) via a second diode (15). [6] Externally excited synchronous machine according to any of the preceding claims, characterized by, that the control electronics (6) includes at least one gate driver (16) for a respective semiconductor switch (17) of the power converter (5), wherein the respective gate driver (16) is powered by the rotor internal power supply means (7) at least in the fallback operating mode. [7] Externally excited synchronous machine according to claim 6, characterized by , that the control electronics (6) additionally includes a processing unit (18) which is configured to determine a respective control signal for the respective gate driver (16) depending on at least one input signal, wherein the control electronics (6) is powered at least in the fallback operating mode by the rotor-internal power supply means (7). [8] Externally excited synchronous machine according to claim 7, characterized by, that a respective sensor (19) of the control electronics (6) is configured to provide the control signal or at least one of the control signals, wherein the respective sensor (6) is powered by the rotor internal power supply means (7) at least in the fallback operating mode. [9] motor vehicle, characterized by , that it comprises a separately excited synchronous machine (2) according to one of the preceding claims. [10] Motor vehicle according to claim 9, characterized by , that the synchronous machine (1) is mechanically coupled to at least one wheel (21) of the motor vehicle (20) in at least one operating state of the motor vehicle (20) in such a way that the synchronous machine (1) drives the wheel (21) as a drive motor.

Images