Fault detection for excitation feed with an asymmetrical half-bridge, by monitoring switching transients

Abstract

The invention relates to an assembly (12) for a converter (13) of a drive unit (10), and to a converter (13). The assembly (12) comprises a control and evaluation unit (38) and an excitation circuit (34). The excitation circuit (34) comprises an asymmetrical half-bridge (48), which has at least a first power switch (54A) and a second power switch (54B). The excitation circuit (34) has a first excitation line (60A) and a second excitation line (60B) for the drive unit (10). The first power switch (54A) is associated with the first excitation line (60A), and the second power switch (54B) is associated with the second excitation line (60B). The excitation circuit (34) has an excitation filter (62), which has a first RC element (70A) coupled to the first excitation line (60A) and a second RC element (70B) coupled to the second excitation line (60B). The control and evaluation unit (38) is connected to the RC elements (70A, 70B) in such a way that a switch-on transient and / or a switch-off transient of the power switch (54A, 54B) associated with the respective excitation line (60A, 60B) can be tapped. The control and evaluation unit (38) is designed to detect a fault state on the basis of the tapped switch-on transient and / or switch-off transient.

Description

[0001] Fault detection for pathogen feeder with asymmetric half-bridge using switching transient monitoring

[0002] The invention relates to an assembly for a converter of a drive unit and a converter.

[0003] Electrically powered vehicles increasingly use separately excited electric motors. This means that the rotor does not have permanent magnets, but rather a rotor winding that is energized with a rotor current to generate a magnetic field. An excitation circuit is used to provide this rotor current, converting energy from a high-voltage storage device into a direct current for rotor excitation.

[0004] Typically, such excitation circuits feature an asymmetrical half-bridge with at least two power transistors. The power transistors are used to drive an excitation current into respective excitation lines that are coupled to the rotor winding.

[0005] Due to aging processes or specific operating conditions, such as an unexpected loss of coolant, a fault can occur, causing one of the power transistors to fail. In this situation, the excitation circuit can initially continue to operate using the complementary second power transistor. However, the second power transistor and other components of the excitation circuit, such as freewheeling diodes, then experience significantly higher load conditions. This greatly increases the load on the remaining, undamaged components. Consequently, after the failure of the first power transistor, typically within a relatively short period, other components or the remaining power transistor of the excitation circuit will also fail.For example, defects can occur within such a short timeframe that a temperature sensor fails to detect the excessively high load conditions that would otherwise cause a corresponding temperature increase. As a result, the entire excitation circuit becomes unusable or can generate excessively high excitation currents, potentially damaging other components, such as the stator of the electric motor. Current approaches only address fault detection mechanisms capable of identifying a complete failure of the excitation circuit. For instance, overcurrent detection can be used to identify excessively high excitation currents. However, in certain fault scenarios, such as the simultaneous shorting of both power transistors in the excitation circuit, it is then no longer possible to interrupt the current flow in the inverter.

[0006] The invention is therefore based on the objective of eliminating or at least reducing the disadvantages of the prior art. In particular, it is desirable to be able to detect faults in an excitation circuit earlier than before, so that appropriate countermeasures can be taken to prevent damage to other components.

[0007] The problem is solved by the subject matter of the independent claims. Advantageous embodiments are specified in the dependent claims and the following description, each of which, individually or in (sub-)combination, can represent aspects of the invention. Some features are explained with regard to assemblies, others with regard to inverters. However, the aspects are interchangeable.

[0008] According to one aspect of the invention, an assembly for a drive unit's converter is provided. The assembly comprises a control and evaluation unit and an excitation circuit. The excitation circuit includes an asymmetrical half-bridge with at least one first circuit breaker and one second circuit breaker. The excitation circuit has a first excitation line and a second excitation line for the drive unit. The first circuit breaker is connected to the first excitation line, and the second circuit breaker is connected to the second excitation line. The excitation circuit includes an excitation filter comprising a first RC element coupled to the first excitation line and a second RC element coupled to the second excitation line.The control and evaluation unit is connected to the RC elements in such a way that a switch-on transient and / or a switch-off transient of the circuit breaker assigned to the respective excitation line can be tapped. The control and evaluation unit is configured to detect a fault condition based on the tapped switch-on and / or switch-off transient. The invention is based on the finding that, using an excitation filter that has separate RC elements for the different excitation lines, the supply signals of the excitation lines can be tapped independently of one another. Since the excitation lines are each individually assigned to a circuit breaker of the excitation circuit, the switch-on and / or switch-off transients of the corresponding circuit breakers can be detected independently of one another.This allows for an evaluation of the recorded switch-on and / or switch-off transients to determine whether fault conditions occur or exist with respect to a single circuit breaker. This fundamentally differs from previously known approaches, as previous methods could only detect a total failure of the excitation circuit. In contrast, this module makes it possible to detect fault conditions where initially only a single circuit breaker is affected.

[0009] This creates the possibility to take countermeasures to prevent a possible total failure of the excitation circuit and / or impermissibly high excitation currents and / or effects on other components, for example the stator of the electric motor of the drive unit.

[0010] In addition, the design of the assembly enables the continuous monitoring of the switch-on and / or switch-off transients for each individual circuit breaker. This allows for particularly rapid detection of fault conditions, enabling continuous fault detection without any significant time delay. As a result, the fault detection mechanism operates with less time delay compared to previous approaches, such as a temperature sensor that detects a temperature increase due to increased excitation currents or load conditions. Temperature-based fault detection, as described here, is time-delayed because the heat conduction paths are complex and the heat capacities of individual components are relatively high.This means that a certain time interval is required before the temperature rise at the location of the temperature sensor is sufficient to exceed a corresponding temperature threshold, and a fault condition is detected based on this temperature increase. In contrast, the assembly enables quasi-instantaneous fault detection, since each individual switch-on and / or switch-off transient of the circuit breakers can be captured and evaluated.

[0011] The term "drive unit" can be understood to mean, in particular, a combination of at least one electric motor and an associated inverter. Naturally, the drive unit may also include other components.

[0012] The electric motor of the drive unit comprises a rotor and a stator. Preferably, the electric motor is designed as a separately excited electric motor, for example, as a separately excited synchronous machine. In this case, the rotor has a rotor winding for which supply signals are provided by the assembly and, in particular, the excitation circuit. In this sense, the rotor winding is at least indirectly coupled to the excitation lines of the excitation circuit.

[0013] The excitation lines represent signal lines by means of which the output signals of the asymmetrical half-bridge of the excitation circuit are provided to downstream components, for example the rotor winding of the rotor.

[0014] Preferably, each power switch comprises a transistor, most preferably a bipolar transistor with an insulated gate electrode. Of course, other transistor types, such as metal-oxide-semiconductor field-effect transistors, can also be used.

[0015] An RC circuit is understood to be a combination of electrical components that includes at least one electrical resistor and one capacitor.

[0016] The turn-on transient refers to an impulse response to a change in the switching state of a power switch from off to on. Because the turn-on process of the power switch, based on a corresponding control signal to the gate electrode, occurs particularly quickly, the resulting output signal of the respective power switch exhibits a significant transient response, at least for a period of time, before the output signal stabilizes. This transient response is the turn-on transient.

[0017] Similarly, the switch-off transient describes an impulse response to a change in the switching state of the power switch from conducting to blocking, which also results in an oscillation of the output signal.

[0018] Since the turn-on and turn-off transients are characteristic of the operating state of the respective circuit breaker, they can be reliably used to determine the operating state and / or a possible fault state of the corresponding circuit breaker. This fundamentally enables fault detection with regard to the entire excitation circuit and assembly.

[0019] Optionally, the circuit breakers are controlled in such a way that they drive a direct current between the first and second excitation lines. This allows, for example, a desired direct current to be driven between the excitation lines, which can then be used as rotor current to power the rotor winding of the electric motor in the drive unit.

[0020] Preferably, the control of the circuit breakers is also carried out by the control and evaluation unit. In this case, the control and evaluation unit can output corresponding control signals, for example, to a gate driver circuit. The gate driver circuit ultimately outputs corresponding gate control signals, such as gate voltage signals, for the gate electrodes of the circuit breakers. Based on these gate control signals, the switching states of the circuit breakers can thus be influenced as required in order to drive a desired current between the excitation lines. In other words, the control and evaluation unit is optionally configured to output control signals for controlling the switching states of the circuit breakers.

[0021] Preferably, the control and evaluation unit for outputting the control signals can include a pulse width modulator (PWM) to tailor the output control signals. For example, signals output by the PWM can be adjusted with respect to frequency and / or duty cycle to influence the switching states of the circuit breakers as desired.

[0022] In some embodiments, the excitation filter for the excitation lines includes a sensor capacitor, which is coupled to a central node between a resistor and a capacitor of the respective RC network. The sensor capacitors allow the signals present in the respective excitation lines to be reliably detected over wide voltage ranges, for example, over a voltage range of 60 V to 900 V, thus covering the typical voltage range of commonly used high-voltage storage devices (approx. 800 V). This makes the application range of the assembly broad.

[0023] Optionally, the excitation circuit for each excitation line includes a balancing circuit. This balancing circuit is designed to output a signal with a specified amplitude in the low-voltage range, specifically 24 V or less, based on the excitation signal present in the respective excitation line. The balancing circuits allow the tapped signals from the excitation lines to be divided down to a predetermined voltage amplitude without losing the characteristic signal features that reflect the switch-on and / or switch-off transients of the circuit breakers. This reduces the voltage amplitude, simplifying the further processing and evaluation of the corresponding signals.

[0024] The respective balancing circuits can be implemented downstream of the excitation filter in the signal processing circuitry. Alternatively, the balancing circuits can also be considered part of the excitation filter.

[0025] Optionally, the control and evaluation unit has at least several digital inputs to which the output signals of the balancing circuits are at least indirectly applied. This allows the output signals provided by the balancing circuits to be digitally acquired and evaluated by the control and evaluation unit. This enables a particularly high signal-to-noise ratio. Furthermore, known digital evaluation mechanisms can be used. In some embodiments, the control and evaluation unit has a digital Schmitt trigger circuit for each RC element of the excitation filter. This incorporates a comparator circuit in which the turn-on and turn-off transients do not coincide but are offset from each other by the switching hysteresis.As a result, the switch-on and switch-off transients can be reliably distinguished from each other, so that each individual switch-on and switch-off transient of a corresponding circuit breaker can be recorded individually.

[0026] The Schmitt trigger circuits can each be arranged, in particular, between the outputs of the balancing circuits and the digital inputs of the control and evaluation unit.

[0027] Preferably, the excitation filter includes at least one common-mode choke that acts between different filter lines of the excitation filter, wherein the different filter lines are coupled to different excitation lines. The common-mode choke attenuates and, in particular, reduces electromagnetic interference, especially common-mode interference. This improves the signal quality in the filter lines.

[0028] Optionally, the common-mode choke can be placed upstream of the sensor capacitors in the signal path. This means that the common-mode choke is located between the excitation circuit and the RC circuits.

[0029] In some embodiments, the time required for the control and evaluation unit to detect switch-on and / or switch-off transients is shorter than a switching period of the asymmetric half-bridge. This ensures that the switch-on and / or switch-off transients are detected before a switching period has elapsed. This makes the detection of a potential fault condition particularly fast. As a result, if a fault condition occurs in the first circuit breaker, the complementary second circuit breaker is only subjected to a high load condition for such a short period that a subsequent fault in the second circuit breaker caused by the load condition can be ruled out, at least if countermeasures are initiated to compensate for the fault condition.This enables the control and evaluation unit to detect, either in hardware or software, every single switching operation of the circuit breakers in the excitation circuit. Should a circuit breaker fail, this would be detected within the same PWM cycle.

[0030] The time required for the control and evaluation unit to detect the switch-on and / or switch-off transients can be, in particular, 400 ps or less, preferably 350 ps or less, more preferably 300 ps or less, more preferably 250 ps or less, and especially 10 ps or more. Since it can be assumed that at least one, or typically several, PWM periods lie between a first fault of a first circuit breaker and a subsequent fault of the complementary second circuit breaker, the still-intact circuit breaker could be used to interrupt the generation of an excitation current driven in the excitation lines, based on a corresponding control signal. This can prevent the risk of a subsequent fault. For example, damage to other components can be prevented.

[0031] Optionally, the time required for the control and evaluation unit to detect the switch-on and / or switch-off transients can even be shorter than the duration of the respective switching state of the circuit breaker. This means that the switch-on and switch-off transients can be detected before the switching state of the corresponding circuit breaker changes again, or should change in the event of a fault. This makes the fault detection mechanism even faster, thus reducing the impact on the assembly and other components.

[0032] Preferably, the control and evaluation unit is configured to detect a fault in the circuit breaker and / or the excitation circuit based on a comparison of the detected turn-on and / or turn-off transients tapped from different RC circuits. This utilizes a particularly efficient and reliable fault detection technique. Since corresponding sensor capacitors and balancing circuits are provided for both excitation lines, the tapped signals should be mutually equivalent. By comparing the respective detection signals, a fault can therefore be identified for a specific circuit breaker or for a part of the electrical circuit associated with a specific circuit breaker.

[0033] Optionally, the control and evaluation unit can also be configured to compare detected switch-on and / or switch-off transients, measured with respect to a specific, individual excitation line, with previous switch-on and / or switch-off transients or a target signal from the same specific excitation lines. This broadens the information base for deciding whether a fault has occurred and allows for an independent decision for each excitation line (and thus for each circuit breaker). This increases the reliability of detecting a fault or its absence.

[0034] In some embodiments, the control and evaluation unit is configured to continue operating the excitation circuit with a fault-free, single circuit breaker at reduced electrical power following a detected fault in one circuit breaker. After a fault occurs in one circuit breaker, the complementary second circuit breaker of the asymmetrical half-bridge would potentially be subjected to an undesirably high load. This would increase the probability of a fault also occurring in the complementary second circuit breaker. Therefore, as an example of a countermeasure, the control and evaluation unit can reduce the electrical power for the fault-free, complementary second circuit breaker so that it can continue operating at the desired reduced electrical power. This reduces the probability of a subsequent fault.Even though the electrical power output is reduced in this case compared to the originally used electrical power, this countermeasure allows the excitation circuit to continue operating and thus supply the rotor with a corresponding rotor current. In this way, the electric motor of the drive unit can still be used without the risk of total failure or damage to other components.

[0035] Preferably, the control and evaluation unit is configured to issue a notification to a user of the assembly via a user interface whenever a fault is detected. This makes it possible to inform the user of the assembly that appropriate maintenance measures are necessary to prevent a total failure of the excitation circuit and thus of the drive unit.

[0036] Preferably, the excitation circuit includes a third power switch arranged between two arms of the asymmetrical half-bridge. The first arm of the asymmetrical half-bridge includes the first power switch and a first freewheeling diode. The second arm of the asymmetrical half-bridge includes the second power switch and a second freewheeling diode. Each excitation line is coupled to a central node between the power switch and the freewheeling diode of the respective arm of the asymmetrical half-bridge.

[0037] This configuration of the excitation circuit allows the first and second power switches to be used to drive current into the excitation lines when the PWM signal is active (high signal amplitude). When the PWM signal is deactivated (low signal amplitude), the previously driven rotor current continues to flow through the third power switch, which has a diode connected in series with it.

[0038] The excitation lines of the excitation control system are balanced against the nominal high-voltage voltage amplitudes (HV+) and HV- to half the HV voltage via balancing resistors. This is called "symmetrical excitation control" and has advantages with regard to EMC interference emissions (EMC: electromagnetic compatibility) via the rotor, whose rotor lines are at least indirectly coupled to the excitation lines.

[0039] Preferably, the excitation circuit for the respective balancing resistors includes a voltage converter configured to generate the output signal. This allows for the evaluation of not only the pure voltage amplitudes and signal characteristics, but also the quality of the balancing implemented by the balancing resistors. This enables the detection of operating conditions where insufficient balancing influences the detection signals, which, without the voltage converter, might be erroneously attributed to other causes. In the event of a fault, the additional freewheeling diodes of the arms of the asymmetric half-bridge can be used to allow the electrical energy stored in the rotor to flow back from the center nodes of the corresponding arms of the asymmetric half-bridge, via the freewheeling diodes, into a high-voltage storage device coupled to the excitation circuit.The freewheeling diodes of the arms of the asymmetrical half-bridge therefore ensure that the rotor coupled to the excitation lines, or rather its rotor winding, and the excitation circuit as a whole can be made power- and torque-free if necessary. This is particularly important, for example, in the event of a collision involving a motor vehicle equipped with the corresponding assembly.

[0040] According to a further aspect, the invention also relates to an inverter for a drive unit of an electric motor vehicle. The drive unit has a separately excited rotor with a rotor winding. The inverter comprises an assembly as described herein. The excitation lines are coupled to the rotor winding. The excitation circuit drives a direct current in the excitation lines, which is used as rotor current to energize the rotor winding of the photograph.

[0041] The advantages achieved by the assembly shown herein are also ensured by the inverter in a corresponding manner.

[0042] According to another aspect, the invention also relates to a motor vehicle with an inverter as described herein or with an assembly as described herein.

[0043] The advantages achieved by the assembly and inverter presented herein are also ensured by the motor vehicle in a corresponding manner.

[0044] For the purposes of the present invention, motor vehicles can include, in particular, land vehicles with an electric machine, namely, among others, three-wheelers, trikes, quads, off-road and on-road vehicles such as passenger cars, buses, trucks, tractors and other commercial vehicles, and rail vehicles (trains) which have at least one electric machine (electric motor) serving to propel the vehicle. Vehicles can be manned or unmanned. In addition to battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs) and fuel cell electric vehicles (FCEVs) can also be included.

[0045] Alternatively, motor vehicles may also include vehicles with internal combustion engines that have at least one electric motor that can be operated with an assembly as described above.

[0046] The invention, as well as further advantageous embodiments and developments thereof, are described and explained in more detail below with reference to the examples shown in the drawings. The features that can be derived from the description and the drawings can be applied individually or in any combination according to the invention. The drawings show:

[0047] Fig. 1 shows a simplified schematic representation of a drive unit with an inverter according to the invention for an electrically powered motor vehicle according to one embodiment.

[0048] Fig. 2 shows a simplified schematic partial representation of an assembly with an excitation circuit according to one embodiment.

[0049] Fig. 3 shows a simplified schematic partial representation of the assembly with an excitation filter and a control and evaluation unit according to one embodiment, and

[0050] Fig. 4 is a schematic representation of a motor vehicle with an assembly according to one embodiment.

[0051] All features disclosed below with reference to the exemplary embodiments and / or the accompanying figures can be combined alone or in any subcombination with features of the aspects of the present disclosure, including features of preferred embodiments, provided that the resulting combination of features is meaningful to a person skilled in the art.

[0052] Fig. 1 shows a simplified schematic representation of a drive unit 10 with an assembly 12 according to the invention, which is part of an inverter 13 according to the invention for an electrically powered motor vehicle according to one embodiment. The inverter 13 is designed as a traction inverter for the electric motor 14, which is also part of the drive unit 10.

[0053] The electric motor 14 is designed here as a separately excited synchronous machine. However, other types of electric motors 14, for example other separately excited machine types, can also be used.

[0054] The electric motor 14 has a stator 16 and a rotor 18.

[0055] Typically, the stator 16 has a three-phase winding set with three stator windings 20.

[0056] In contrast, rotor 18 has only a single rotor winding 22.

[0057] Both the stator 16 and the rotor 18 are connected to the converter 13 via supply lines 24. The converter 13 can provide corresponding supply signals to the stator windings 20 and the rotor winding 22 via these supply lines 24. The currents driven in the supply lines 24 can be detected by current sensors 26.

[0058] Additionally, a rotor position sensor 28 is coupled to the electric motor 14, which can detect the rotor position of the rotor 18 relative to the stator 16. This also allows the rotational speed of the rotor 18 to be determined.

[0059] When the stator windings 20 and the rotor winding 22 are appropriately energized, the rotor 18 is subjected to a torque. This allows the rotor 18 to move relative to the stator 16, provided sufficient torque is generated considering the external mechanical load conditions, so that a torque can be used via an output shaft to drive a driveable component 30.

[0060] To provide the supply signals for the stator windings 20, the converter 13 conventionally includes a sub-converter 32, which can output the corresponding supply signals for the supply lines 24. For example, the sub-converter 32 can be configured as a B6 bridge with three half-bridges. To be able to provide the corresponding supply signals for the rotor winding 22 of the rotor 18, the converter 13 also includes an excitation circuit 34 as part of the assembly 12. Excitation currents can be generated by means of the excitation circuit 34, which are used as rotor current in the rotor 18 for the rotor winding 22.

[0061] The electrical energy is provided by a direct current source, for example a high-voltage storage device 36, which is coupled to both the partial converter 32 and the excitation circuit 34.

[0062] Furthermore, the assembly 12 of the drive unit 10 has a control and evaluation unit 38, which includes at least one data processing device 40.

[0063] According to this embodiment, the control and evaluation unit 38 additionally has a pulse width modulator 42 (PWM) and a current controller 44 coupled to the PWM 42.

[0064] The current controller 44 determines control signals, which are transmitted to the PWM 42, based on a comparison of the target currents of the stator windings 20 and the rotor winding 22 with the actual currents, which can be detected by the current sensors 26, taking the rotor position into account. The rotor position of the rotor 18 relative to the stator 16 can be determined using the rotor position sensor 28.

[0065] The PWM 42 then determines digital control signals for gate driver circuits 46, which are assigned to the respective power switches of the sub-converter 32 and the excitation circuit 34, in order to supply the gate electrodes of the corresponding power switches with the required gate voltages. This allows the switching states of the power switches of the sub-converter 32 and the excitation circuit 34 to be influenced, ultimately enabling the provision of required supply signals for the stator windings 20 and the rotor winding 22.

[0066] Fig. 2 shows a simplified schematic partial representation of an assembly 12 with an excitation circuit 34 according to one embodiment. The excitation circuit 34 comprises an asymmetrical half-bridge 48 with a first arm 50A and a second arm 50B.

[0067] Both arms 50A, 50B are coupled to two supply nodes 52A, 52B, at which the excitation circuit 34 receives high-voltage signals of different polarity, for example from the high-voltage storage 36.

[0068] Starting from the first supply node 52A, the first arm 50A has a first power switch 54A (also called Q1) and a first freewheeling diode 56A (also called D4) arranged in series with it and oriented in reverse direction.

[0069] Starting from the second supply node 52A, the second arm 50B has a reverse-biased second freewheeling diode 56B (also called D5) and a second power switch 54B (also called Q2) arranged in series with it.

[0070] Additionally, the first arm 50A between the first power switch 54A and the first freewheeling diode 56A has a first center node 58A (also called M1), from which, using the first excitation line 60A (also called AC1), a first output signal of the excitation circuit 34 is provided.

[0071] Similarly, the second arm 50B has a second central node 58B (also called M2) between the second freewheeling diode 56B and the second power switch 54B, from which a second output signal of the excitation circuit 34 is provided via the second excitation line 60B (also called AC 2).

[0072] In addition, the excitation circuit 34 has a central arm between the first arm 50A and the second arm 50B, in particular between the first central node 58A and the second central node 58B, which has a third power switch 54C starting from the first arm 50A and a third diode 56C arranged in series with it, designed in reverse direction and assigned to the third power switch 54C.

[0073] Furthermore, the excitation circuit 34 for all power switches 54A to 54C has diodes connected in parallel. According to this embodiment, the power switches 54 are designed as bipolar transistors with an insulated gate electrode.

[0074] Therefore, corresponding gate signals G1 to G3 are provided for the gate electrodes of the power switches 54 by the gate driver circuit 46 in order to influence the switching states of the power switches 54.

[0075] Since the gate control signals for the gate electrodes of the power switches 54 are provided based on the PWM 42 of the control and evaluation unit 38, the first and second power switches 54A and 54B are supplied with gate signals such that, during the active phase of the PWM signal (high amplitude), a current is driven into the excitation lines 60A and 60B. In this case, the first power switch 54A and the second power switch 54B are in the conducting state. The third power switch 54C is permanently switched on (conducting) during operation, so that the third diode 56C is reverse-biased.As a result, a current flows in the excitation circuit 34, starting from the supply node 52A via the first circuit breaker 54A to the first intermediate node 58A, into the first excitation line 60A, through the rotor winding 22 of the rotor 18 and back via the second excitation line 60B, the second intermediate node 58B, the second circuit breaker 54B and from there to the supply node 52B. In this way, an excitation current can be provided which can be used as rotor current for the rotor winding 22 of the rotor 18 of the electric motor 14.

[0076] In the deactivated phase of the PWM signal (low amplitude), the first power switch 54A and the second power switch 54B are off. The third power switch 54C is conducting. The third diode 56C is now energized in the forward direction. This allows the rotor current excited in the rotor winding 22 of the rotor 18, originating from the second excitation line 60B, to flow back into the rotor winding 22 of the rotor 18 via the second center node 58B, the third diode 56C (associated with the third power switch 54C), the third power switch 54C (connected in series with the third diode 56C), the first center node 58A, and the first excitation line 60A. Thus, in this state, the excited rotor current circulates through the third power switch 54C and its associated third diode 56C, remaining largely constant.In specific fault conditions of the excitation circuit 34 or of another component of the power supply of the electric motor 14 or of the electric motor 14 itself, or in the event of another relevant incident (for example, a collision of the underlying vehicle), the excitation circuit 34 must be de-energized. Additionally, in this case, it must be ensured that the electric motor 14 is torque-free. This means that no torque should be generated at the output of the electric motor 14. To achieve this, the rotor current excited in the rotor winding 22 of the rotor 18 must be dissipated, for example, by feeding the corresponding amounts of energy back into the high-voltage storage device 36. For this purpose, in such a fault condition, the circuit breakers 54A to 54C are supplied with gate signals G1 to G3 such that they are switched off.The energy underlying the rotor current, which was excited in the rotor winding 22 of the rotor 18, can then be fed back to the supply nodes 52A, 52B via the freewheeling diodes 56A, 56B, so that the energy can flow into the high-voltage storage device 36. In this way, a power and torque-free state of the rotor 18 can be ensured within a few milliseconds as soon as the rotor current is zero, for example, within 30 ms or less, preferably within 10 ms or less, and more preferably within 5 ms or less.

[0077] Fig. 3 shows a simplified schematic partial representation of the assembly 12 with an excitation filter 62 and a control and evaluation unit 38 according to one embodiment.

[0078] The first excitation line 60A (AC1) is coupled to the positive high-voltage amplitude (HV+) via balancing resistors 61A. The second excitation line 60B (AC2) is coupled to the negative high-voltage amplitude (HV-) via balancing resistors 61B. The balancing resistors 61A and 61B can each be implemented as single resistors or, alternatively, as circuits with multiple resistors. The balancing resistors 61A and 61B ensure that the excitation drive is statically balanced to half the high-voltage amplitude. This is called "symmetrical excitation drive" and offers advantages with regard to EMC emissions. The excitation filter 62 has a first filter line 64A and a second filter line 64B. The first filter line 64A is coupled to the first excitation line 60A. The second filter line 64B is coupled to the second filter line 60B.

[0079] The first filter line 64A is coupled to the second filter line 64B via a common-mode choke 66 of the excitation filter 62. The common-mode choke 66 attenuates common-mode interference between the first filter line 64A and the second filter line 64B. This improves the electromagnetic compatibility of the rotor current ultimately supplied to the rotor winding 22 of the rotor 18.

[0080] Downstream of the common-mode choke 66 are tap nodes 68A, 68B for the respective filter lines 64A, 64B.

[0081] Each tap node 68A, 68B is subsequently coupled to an RC element 70A, 70B, wherein a respective capacitor 72A, 72B is arranged between the respective resistor 74A, 74B of the RC element 70A, 70B and the respective tap nodes 68A, 68B.

[0082] Additionally, the resistors 74A, 74B of the RC elements 70A, 70B are coupled to ground 76 (or alternatively a reference potential).

[0083] The capacitors 72A, 72B of the RC elements 70A, 7B can be considered part of the excitation filter 62.

[0084] Between the capacitors 72A, 72B and the respective resistors 74A, 74B of the RC elements 70A, 70B, additional center nodes 78A, 78B are arranged, each of which is coupled to a sensor capacitor 80A, 80B.

[0085] The sensor capacitors 80A and 80B allow the subsequently evaluated signals to be reliably tapped and evaluated over wide voltage ranges, for example, over a voltage range from 60 V to 900 V. This allows correspondingly different voltage amplitudes to be taken into account, even though the high-voltage storage device 36 typically has a maximum voltage amplitude of 800 V. The sensor capacitors 80A and 80B are coupled oppositely to the center nodes 78A and 78B via respective balancing circuits 82A and 82B.

[0086] The balancing circuits 82A and 82B can be configured in various ways. According to this embodiment, the balancing circuits 82A and 82B include at least several resistors and other electrical components, such as diodes and / or capacitors, which allow the tapped voltage amplitudes to be divided into the low-voltage range with maximum amplitudes of 24 V. Reducing the voltage amplitude simplifies the subsequent evaluation of the tapped signals.

[0087] Alternatively, the balancing resistors 61 A, 61 B can also include respective voltage converters configured to generate the output signals.

[0088] The output signals of the balancing circuits 82A and 82B are then fed to the respective Schmitt trigger circuits 84A and 84B, each of which has at least one comparator. The comparators allow the tapped signals to be evaluated with regard to their turn-on and / or turn-off transients.

[0089] The outputs of the Schmitt trigger circuits 84A, 84B are fed to digital inputs 86A, 86B of the control and evaluation unit 38.

[0090] Alternatively, the Schmidt trigger circuits 84A, 84B can also be considered part of the control and evaluation unit 38. In this case, the digital inputs 86A, 86B can be coupled to the outputs of the balancing circuits 82A, 82B.

[0091] Since the filter lines 64A and 64B are each individually coupled to the excitation lines 60A and 60B, and the correspondingly filtered signals are fed to individual RC elements 70A and 70B at the tap nodes 68A and 68B, the turn-on and / or turn-off transients of the circuit breakers 54A and 54B can be evaluated separately and independently. This is made possible by assigning the excitation lines 60A and 60B to individual circuit breakers 54A and 54B via the center nodes 58A and 58B. The comparators of the Schmitt trigger circuits 84A and 84B allow a comparison with reference potentials, such as previously acquired signals or setpoints, thereby enabling the detection of variations that indicate a fault condition of a specific circuit breaker 54A or 54B, or of another part of the assembly 12.The assembly 12 is designed with respect to the excitation filter 62 and the components involved in the evaluation such that the evaluation of the tapped signals can take place within very short time periods. In particular, the evaluation of the tapped signals can be carried out so quickly that it is possible within one period of the PWM signal provided by the PWM 42, which corresponds to one switching period of the asymmetric half-bridge 48.

[0092] This enables the control and evaluation unit 38 to take countermeasures to avoid undesirably high load conditions for individual fault-free circuit breakers 54. For example, after detecting a fault in a specific circuit breaker 54, the control and evaluation unit 38 can adjust the control signals, such as the PWM signal, to operate the remaining fault-free circuit breaker 54 at a reduced power. This reduces the load condition for the remaining fault-free circuit breaker 54.

[0093] While previous approaches could only identify faults involving a total failure of the excitation circuit 34, the assembly 12 enables the identification of faults relating to individual circuit breakers 54, and also allows the identification of the faulty circuit breaker 54. Additionally, countermeasures can be taken based on this information to enable the continued operation of the electric motor 14 of the drive unit 10, for example, in a reduced-power operating mode.

[0094] Fig. 4 shows a schematic representation of a motor vehicle 90 with an assembly 12 according to one embodiment.

[0095] The motor vehicle 90 has driven wheels 92 which are coupled to an electric motor 14 for propulsion. The electric motor 14 is part of the drive unit 10 and is supplied with appropriate supply signals by the inverter 13 assembly 12 to ensure propulsion for the motor vehicle 90.

[0096] This application may refer to quantities and numbers. Unless expressly stated otherwise, such quantities and numbers are not to be considered limiting, but rather as examples of the possible quantities or numbers in connection with this application. In this context, the term "plural" may also be used in this application to refer to a quantity or number. In this context, "plural" means any number greater than one, e.g., two, three, four, five, etc. The terms "about," "approximately," "close," etc., mean plus or minus 5% of the stated value.

Claims

Patent claims 1. Assembly (12) for a converter (13) of a drive unit (10), comprising a control and evaluation unit (38) and an excitation circuit (34), wherein the excitation circuit (34) comprises an asymmetrical half-bridge (48) with at least one first circuit breaker (54A) and a second circuit breaker (54B), wherein the excitation circuit (34) has a first excitation line (60A) and a second excitation line (60B) for the drive unit (10), wherein the first circuit breaker (54A) is assigned to the first excitation line (60A) and the second circuit breaker (54B) is assigned to the second excitation line (60B), wherein the excitation circuit (34) has an excitation filter (62) comprising a first RC element (70A) coupled to the first excitation line (60A) and a second RC element (70B) which is coupled to the second excitation line (60B), wherein the control and evaluation unit (38) is connected to the RC elements (70A, 70B) in such a way,that a switch-on transient and / or a switch-off transient of the circuit breaker (54A, 54B) assigned to the respective excitation line (60A, 60B) can be tapped, and wherein the control and evaluation unit (38) is configured to detect a fault condition based on the tapped switch-on transient and / or switch-off transient.

2. Assembly (12) according to claim 1, characterized in that the excitation filter (62) for the excitation lines (60A, 60B) each has a sensor capacitor (80A, 80B) which is coupled to a central node (78A, 78B) between a resistor (74A, 74B) and a capacitor (72A, 72B) of the respective RC element (70A, 70B).

3. Assembly (12) according to claim 1 or 2, characterized in that the excitation circuit (34) for the excitation lines (60A, 60B) each has a balancing circuit (82A, 82B) which is configured to output an output signal with an output voltage with a target amplitude in the low-voltage range, in particular equal to or less than 24 V, based on an excitation signal present in the respective excitation line (60A, 60B) with an excitation voltage amplitude.

4. Assembly (12) according to claim 3, characterized in that the excitation circuit (34) for respective balancing resistors (61 A, 61 B) has a It has a voltage converter that is set up to generate the output signal.

5. Assembly (12) according to claim 3 or 4, characterized in that the control and evaluation unit (38) has at least several digital inputs (86A, 86B) to which the output signals of the balancing circuits (82A, 82B) are at least indirectly applied.

6. Assembly (12) according to one of the preceding claims, characterized in that the control and evaluation unit (38) has a digital Schmidt trigger circuit (84A, 84B) for each RC element (70A, 70B) of the excitation filter (62).

7. Assembly (12) according to one of claims 1 to 3, characterized in that the control and evaluation unit (38) has an analogous Schmidt trigger circuit (84A, 84B) for each RC element (70A, 70B) of the excitation filter (62).

8. Assembly (12) according to one of the preceding claims, characterized in that the excitation filter (62) has at least one common common-mode choke (66) which acts between different filter lines (64A, 64B) of the excitation filter (62), wherein the different filter lines (64A, 64B) are coupled to different excitation lines (60A, 60B).

9. Assembly (12) according to one of the preceding claims, characterized in that the control and evaluation unit (38) is configured to output control signals for controlling the switching states of the circuit breakers (54).

10. Assembly (12) according to claim 9, characterized in that the control and evaluation unit (38) has a pulse width modulator (42) for outputting the control signals.

11. Assembly (12) according to one of the preceding claims, characterized in that the time period for detecting switch-on transients and / or switch-off transients by the control and evaluation unit (38) is shorter than a switching period of the asymmetric half-bridge (48).

12. Assembly (12) according to claim 11, characterized in that the control and evaluation unit (38) is configured to detect a fault in the circuit breakers (54) and / or the excitation circuit (34) based on a comparison of the detected switch-on transients and / or switch-off transients that have been tapped from different RC elements (70A, 70B).

13. Assembly (12) according to claim 12, characterized in that the control and evaluation unit (38) is configured to continue operating the excitation circuit (34) with a fault-free, single circuit breaker (54) with reduced electrical power as a result of a detected fault of a circuit breaker (54).

14. Assembly (12) according to one of the preceding claims, characterized in that the excitation circuit (34) has a third power switch (54C) arranged between two arms (50A, 50B) of the asymmetric half-bridge (48), wherein the first (50A) arm of the asymmetric half-bridge (48) has the first power switch (54A) and a first freewheeling diode (56A), wherein the second arm (50B) of the asymmetric half-bridge (48) has the second power switch (54B) and a second freewheeling diode (56B), and wherein an excitation line (60A, 60B) is coupled to a central node (58A, 58B) between the power switch (54) and the freewheeling diode (56) of the respective arm (50) of the asymmetric half-bridge (48).

15. Inverter (13) for a drive unit (10) of an electric motor vehicle (90), wherein the drive unit (10) has a separately excited rotor (18) with a rotor winding (22), wherein the inverter (13) has an assembly (12) according to one of the preceding claims, and wherein the excitation lines (60A, 60B) are coupled to the rotor winding (22).

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