EP3083318A1

EP3083318A1 - Safety circuit arrangement for an electrical drive unit

Info

Publication number: EP3083318A1
Application number: EP14799392.7A
Authority: EP
Inventors: Jose Lopez de Arroyabe
Original assignee: Bayerische Motoren Werke AG
Current assignee: Bayerische Motoren Werke AG
Priority date: 2013-12-19
Filing date: 2014-11-13
Publication date: 2016-10-26
Also published as: WO2015090746A1; DE102013226763A1; US20160226410A1; CN105636820A; US9806649B2; CN105636820B; JP2017502633A

Abstract

The invention relates to a safety circuit arrangement for an electrical drive unit, wherein the electrical drive unit includes a traction battery, an intermediate circuit capacitor connected in parallel to the traction battery, and an electric motor which can be supplied with electrical power by the traction battery, the electric motor having a plurality of phases which can be connected to the traction battery by means of a controllable inverter having a plurality of switch elements, having a discharge circuit which is designed to take a predeterminable discharge current from the intermediate circuit capacitor in the activated operational state of the discharge circuit, having a short-circuit control circuit which is designed to short-circuit at least some of the phases of the electric motor by controlling some of the switch elements in the activated operational state of the short-circuit control circuit, having a supply voltage circuit which is designed to provide a supply voltage on the basis of input voltage delivered to the supply voltage circuit, an intermediate circuit voltage applied to the intermediate circuit capacitor being delivered as input voltage, and having an activating element is designed to close an activation path when a switch-on condition is present in order to activate the discharge circuit and the short-circuit control circuit by providing the supply voltage.

Description

Safety circuit arrangement for an electric drive unit

The invention relates to a safety circuit arrangement for an electric drive unit wherein the electric drive unit a

Traction battery, a parallel to the traction battery intermediate circuit capacitor and an electric power supplied by the traction battery electric machine. The electric machine has a plurality of phases, which are connectable to the traction battery via a controllable, having a plurality of switch elements inverter.

Such constructed electric drive units can be used in many ways. Among other things, they can be used as a drive unit in a vehicle, wherein the vehicle may be designed as a hybrid vehicle or as an electric vehicle. In a hybrid vehicle in addition to the electric machine another unit is used for the drive, usually an internal combustion engine. Whereas an electric vehicle is driven exclusively by an electric machine. The electrical machines used are generally designed as internal rotor machines, in which a rotatably mounted rotor is enclosed by a stationary stator. The stator generates a rotating magnetic field, through which the rotor is taken. The rotor has a rotor shaft, which is technically connected to a drive shaft of the Fährzeugs. As electrical machines synchronous machines, in particular hybrid synchronous machines can be used, the preferential example, are designed as permanently excited synchronous machines. In a hybrid synchronous machine is a permanent magnet synchronous machine, which also has a strong, caused by a correspondingly selected rotor geometry reluctance effect, which is used for the generation of the torque acting on the rotor with. A traction battery is a high-voltage battery that can have a level of spitting that can be on the order of 250 to 450 volts. Preferably, one is

Traction battery built from Li-ion storage cells

In order to ensure safe handling of an electric drive unit, in particular when the electric drive unit is arranged in a vehicle and the electric machine is designed as a permanently excited synchronous machine, various safety measures are to be provided.

On the one hand, care must be taken to ensure that the high voltage applied to the intermediate circuit capacitance can be reduced by the discharge of the intermediate circuit capacity when certain conditions or in certain operating states of the vehicle are present or occurring. This safety measure is to ensure that, for example, in the idle state of the vehicle, the DC link capacity is de-energized and thus, for example, carried out curing workers contact with the potentially dangerous for people high voltage is excluded; in a vehicle, a safety circuit arrangement designed especially for carrying out this safety measure is provided.

On the other hand, safety measures must also be provided with regard to the electrical machine, in particular if it is a permanent-magnet electric machine. In the case of permanent-magnet electric machines, the reason for their operation is that due to the relative movement between the stator windings occurring and inducing a reverse voltage in the stator windings, referred to as the pole wheel voltage, to the permanent magnets. As the speed increases, the pole wheel voltage increases until, during operation of the electric machine, it lies in the range of the supply voltage provided by the traction battery for the electric machine. Is now connected to the DC link and thus the intermediate circuit no voltage source, that is, for some reason, the compound of

Traction battery with the Zwischenkreiskapazitat or the intermediate circuit interrupted, so the Polradspannung can be applied to the DC link capacitance. This can lead to damage to the DC link capacitance and / or to components of the inverter, in particular to the switch elements. In order to avoid such damage, provision is made for the presence or occurrence of certain conditions or in certain operating conditions, in particular if the

Traction battery is not connected to the Zwischenkreiskapazitat that the phases of a permanent-magnet electric machine are short-circuited by a corresponding control of the switching elements of the inverter. Also for carrying out this safety measure, a safety circuit arrangement specially designed for this purpose is provided in a vehicle.

Both for the unloading of the DC link capacitance and for the short-circuiting of the phases of the electrical machine, in particular a permanently excited electrical machine, the safety circuit arrangements designed for this purpose are to be activated or supplied with a corresponding supply voltage. In particular, in this aspect, the known safety circuit arrangements are not yet optimal Thus, in certain operating conditions of the vehicle, for example in an accident in which due to external influences on the vehicle supply of the safety circuit arrangements with electrical energy neither on the Traktiönsbatterie still on the Starter battery is more possible, no sufficient or time-consistent For this reason, supply of the safety circuit arrangements is ensured, and, on the one hand, it is not ensured that the DC link capacitance is discharged to a level at which the DC link capacitance achieves a voltage which is harmless to humans, and, secondly, a long-lasting short circuiting of the phases of the permanently excited electrical machine

In addition, the known safety circuit arrangements also have regard to the number of components required for realizing the respective safety measure and, consequently, the installation space required for the construction of the safety circuit arrangement, as well as the heat development occurring in the safety circuit arrangements , Need for improvement.

It is therefore an object of the present invention to provide an improved safety circuit arrangement, which, even if a supply of electrical energy is possible neither via the traction battery nor the starter battery, both a discharge of the DC link capacity to a level at which a Sets the people harmless voltage, as well as a long-lasting short-circuiting of the phases of an electrical machine, in particular a permanent-magnet electric machine enabled. In addition, the safety circuit arrangement should be improved or optimized with regard to the number of required electrical or electronic components, with regard to the required installation space and with regard to the heat development that occurs during their operation. That The safety circuit should be constructed from as few as possible components, require a very small space and also have a very low heat generation during operation. In addition, the manufacturing costs for the safety circuit arrangement should be low.

This object is achieved by a safety circuit arrangement of the type mentioned, comprising the following means: a A discharge circuit, which is designed to short-circuit in its activated operating state by driving a portion of the switching elements at least a portion of the phases of the electric machine, a supply voltage circuit, which is adapted to remove in their activated operating state of the DC link capacitance a predetermined discharge current which is designed to provide a supply voltage starting from an input voltage fed to it, wherein an intermediate circuit voltage applied to the intermediate circuit capacitance is supplied as input voltage, and an activation element which is designed to close an activation path in the presence of a switch-on condition to the discharge circuit and the short-circuit control circuit by providing the supply voltage.

The safety circuit arrangement according to the invention is based on several ideas. According to a first idea, a supply circuit arrangement is provided in the safety circuit arrangement according to the invention, to which the intermediate circuit voltage applied to the intermediate circuit capacitance is supplied as input voltage in order to be able to provide a supply voltage starting from this intermediate circuit voltage. Thus, a supply of the safety circuit arrangement with electrical energy is ensured even if a supply neither by the traction battery still by the starter battery (voltage level, for example, 12 volts) is possible, for example in an interruption of the supply lines. Thus, even with a simultaneous failure of traction battery and starter battery both a discharge of the DC link capacity to a level at which sets a harmless to human tension, as well as a long-lasting shorting the phases of a permanent-magnet electric machine possible.

According to a second idea, the safety circuit arrangement contains both a discharge circuit and a short-circuit control circuit. Consequently The resulting synergies can be exploited, which leads, for example, to a reduction in the components required for the realization of the

Discharge functionality on the one hand and for the realization of the short-circuit functionality on the other hand needed. Likewise, by incorporating both functionalities into circuitry, the space required to construct the circuitry, i.e., space, is reduced. It reduces the size of the required for the placement of the circuit board or PCB. The circuit board and thus the safety circuit arrangement can be realized much more compact. The reduction in the number of components, which include high-voltage resistors, power transistors and diodes also has the positive side effect that the heat generation on the circuit board supporting the circuit and thus the heat input into the board is lower in addition reduce overall due the lower number of components and the smaller space requirement the manufacturing costs,

According to a third idea can be combined with the safety circuit arrangement according to the invention, i. At the same time, the phases of an electrical machine are short-circuited and, on the other hand, a DC link capacitance and thus the DC link are discharged. Thus, the highest level of safety for an electric drive unit can be achieved with little effort and with a high reliability. It can thus simultaneously discharge a DC intermediate circuit and short-circuit all terminals of an electric induction machine. This is achieved in particular by virtue of the fact that the activation element connects the supply voltage circuit on the one hand and the discharge circuit and the short-circuit control circuit on the other via an activation path

The above object is therefore completely solved. Before discussing advantageous embodiments of the safety circuit arrangement according to the invention, it should be mentioned at this point that the reference made above to a permanent-magnet electric machine should have no restrictive effect. Of course, the safety circuit arrangement according to the invention can also be used in differently constructed electrical machines,

Advantageously, the discharge circuit is designed to be controllable, so that it is possible to set the discharge current taken from the intermediate circuit capacitance.

Preferably, the short-circuit control circuit is designed to short-circuit all phases of the electrical machine in its activated operating state by driving the switch elements. This measure achieves maximum safety.

As already stated, the electric drive unit is preferably arranged in a vehicle. Consequently, the switch-on condition is advantageously given when at least one of the following situations exists:

Guiding the vehicle from a driving condition to a resting condition or

- shut down the traction battery, or

- Presence of a different from the normal driving condition critical driving condition.

When transferring the vehicle from a driving state in which the vehicle is driven by the electric machine, to an idle state in which the vehicle is stationary, and in particular the electric machine is no longer connected to the traction battery and thus the DC link capacity is for To ensure that the unloaded circuit capacity. At the beginning of the idle state, the voltage applied to the DC link capacitance corresponds to the high voltage provided by the traction battery. Consequently, when the idle state occurs, the DC link capacitance is to be discharged, as far as possible, very quickly to a level at which a voltage which is harmless to human beings sets. This is achieved with the safety circuit arrangement according to the invention. Alternatively, the switch-on condition may be given when it is detected on the presence of a decommissioning state.

In determining the shutdown of the traction battery is to ensure that on the one hand, the DC link capacity for reducing the voltage applied to it, which corresponds directly to the beginning of shutdown of the traction battery supplied by the traction battery high voltage is discharged, and on the other hand, the phases of the electric Machine are short-circuited, so that can build up on these no tensions. This is also achieved with the safety circuit arrangement according to the invention. Alternatively or additionally, a traction battery condition condition can be detected and evaluated, which, for example, gives an indication of the charge state of the traction battery and / or of a defect present in the traction battery.

If it is determined that there is a critical driving condition other than the normal driving condition, safety measures must also be taken. In a critical driving condition may be, for example, a driving condition in which very large accelerations, especially lateral acceleration but also longitudinal acceleration, and / or large yaw rate occur, all of which are indicative of a spin, as in an accident or at a Ride may be present at the due to a driver specification, the physically related limits, for example, with respect to the static friction, in particular with respect to a Cornering, are exceeded. In this case, it is also advisable to firstly discharge the DC link capacitance as quickly as possible and, secondly, to short-circuit the phases of the electrical machine. The aforementioned variables can advantageously be detected in each case by means of suitable sensors.

Alternatively and / or additionally, a machine condition condition can be detected and evaluated.

In a preferred embodiment of the invention, the supply voltage circuit is a series circuit consisting of an electrical supply resistor and a Zener diode. This is a simple, reliable and cost-effective measure to provide the supply voltage required for the operation of the safety circuit arrangement. The effort or the need for the realization of a supply voltage circuit is thus reduced to a minimum. At the same time, the circuit thus constructed allows, even when the discharge circuit is not activated, a passive discharge of the DC link capacitance.

In a further preferred embodiment of the invention, the discharge circuit is a series circuit comprising an electrical load resistor and a controllable semiconductor element. This measure is characterized by its monotonous and cost-effective design, while high reliability. At the same time, the discharge current can be adjusted in a simple manner. Preferably, the semiconductor element is a bipolar transistor.

In a further preferred embodiment of the invention, the safety circuit arrangement further comprises a monitoring circuit. This monitoring circuit is configured to process an electrical signal representing a temperature present at the load resistor. Thus, in an unfavorable course of the temperature of the load resistor, this temperature is determined essentially by the discharge current flowing through the load resistor, especially when the temperature approaches a predetermined limit or has even exceeded this, temperature-influencing measures are taken, in particular Measures can be taken that cause the temperature no longer rises, but preferably is lowered, Consequently, the monitoring circuit is adapted to control the controllable semiconductor element in response to a determined monitoring result. As a result, it is possible to set the value of the discharge current taken from the intermediate circuit capacitance, preferably to reduce it. In an extreme case, the semiconductor element can be controlled such that a discharge line through which the discharge current flows is interrupted or opened, and thus no discharge current flows, ie the discharge current assumes the value zero. The load resistance is the main load for the load actively induced discharge of the DC link capacitance.

In a preferred embodiment of the aforementioned measure, the monitoring circuit comprises a measuring bridge circuit constructed from electrical measuring resistors, wherein: one of the measuring resistors is designed as a temperature-dependent resistor. This is a particularly easy-to-implement measure to detect the temperature present at the load resistance, which is also very reliable and at the same time enables precise temperature detection. Consequently, the temperature-dependent resistance is structurally close to the load resistance; arranged so that the signal to be processed by the monitoring circuit electrical signal represents the temperature present at the load resistor as precisely as possible.

In an advantageous embodiment of the aforementioned measure, the temperature-dependent resistor has a negative temperature coefficient on. By using a measuring resistor designed in this way, a reliable and precise detection of the temperature present at the load resistor can be realized in a simple manner.

In a preferred embodiment of the invention, the safety circuit arrangement further comprises a stabilization circuit, which is arranged in terms of circuitry between the supply voltage circuit and the activation element. With this measure, it is ensured that a sufficiently large current for the required to short circuit the phases of the electrical machine driving the switch elements of the inverter can be provided. Thus, a reliable short-circuiting of the phases of the electric machine is ensured.

Advantageously, the inverter has a plurality of half-bridges, wherein each half-bridge has a first and a second switch element, wherein the first switch element is connected to a supply pole of the traction battery and the second switch element is connected to a ground pole of the traction battery. In the case of the safety circuit arrangement according to the invention, the short-circuit control circuit is preferably designed to control the second switching elements connected to the ground pole. This is a measure with which it is possible to control the switch elements for short-circuiting the phases of the electrical machine without great circuitry expense. Alternatively, however, it is also conceivable to design the short-circuit control circuit such that the switch elements connected to the supply pole of the traction battery short-circuit the phases of the electric machine are controlled.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it: 1 based on a circuit diagram, the connection of a safety circuit according to the invention to an electric drive unit,

2 based on a circuit diagram, the structure of the safety circuit according to the invention, and

FIG. 3 shows, by way of a circuit diagram, an exemplary structure of a superposition circuit arrangement contained in the drive unit.

1 shows an electric drive unit 10 and a safety circuit arrangement 12 provided for this purpose. The electric drive unit 10 has a traction battery 14, which can provide a high voltage U _B. To the traction battery 14, a DC link capacitor 16 is connected in parallel. By the traction battery 14, an electrical machine 18 is supplied with electrical energy. The electrical machine 18 has a multiplicity of phases 20, 22, 24, which can be connected to the traction battery 14 via an inverter 28 which can be controlled by a drive unit 26. The inverter 28 has a plurality of switch elements T1, T2, T3, T4, T5, T6, which are arranged in half bridges, one of which is denoted by the reference numeral 30 by way of example. Each of these half bridges 30 has in each case a first switch element 32 and a second switch element 34, the first switch element 32 being connected to a supply pole 36 of the traction battery 14 and the second switch element 34 being connected to a ground pole 38 of the traction battery 14. In Fig. 1, only a first and a second switch element are designated by the reference numerals 32 and 34, respectively. To each of the switch elements T1, T2, T3, T4, T5, T6, a freewheeling diode is connected in parallel, one of which is designated by the reference numeral 40 by way of example. In Fig. 1, the switch elements are designed as IGBTs. This is not intended to be limiting. Of course, other semiconductor devices may be used, such as MOSFETs. FIG. 1 also shows a computing unit 42. With the arithmetic unit 42, starting from a desired torque value, which represents the torque to be generated by the electric machine 18, duty cycle values d _{1 are} determined which are supplied to the drive unit 26 and those in the drive unit 26 in drive signal A for the shift elements T1, T2, T3 , T4, T5, T6 are implemented,

The safety circuit arrangement 12 is now integrated in such a way that the drive signal Bj generated by it, with which the switch elements T1, T2, T3, T4, T5, T6 are driven to short-circuit the phases 20, 22, 24, are likewise supplied to the drive control unit 26. For short-circuiting the phases 20, 22, 24, the switcher stages T1, T2, T3, T4, T5, T6 are driven in such a way by means of the drive signal Bi that the switch elements T1. T3, T5 lock and the switch elements T2, T4, T6 are turned on. The drive unit 26 is designed so that the Ansteuersignaie Bi are superimposed on the Ansteuersignaien Ai. This can be done, for example, in the form that the Ansteuersignaie Bi are given priority before the Ansteuersignaien A _l . An exemplary embodiment of a circuit arrangement with which a superposition of the drive signals Ai and Si can take place is described in conjunction with FIG.

By an interruption 44 is indicated in Fig. 1, that the

Traction battery 14 (active) can be disconnected, z. B. when the vehicle is parked by the driver, or (passively) may fail, for example, characterized in that a supply line is interrupted, which may occur, for example, in an accident.

2, the structure of the safety circuit arrangement according to the invention is shown

The safety circuit arrangement 12 has a supply voltage circuit 46, which is designed to be accessible from one of them Terminals 48, 50 supplied input voltage U _E supply a supply voltage U _V. As can be seen in the illustration in FIG. 1, the input voltage U _E is the intermediate circuit voltage U _Z applied to the intermediate circuit capacitance 16 _, which in turn corresponds to the high voltage U _B provided by the traction battery 14. As shown in FIG 2, the supply voltage circuit 46 is implemented as a series connection of an electrical supply resistor 52 and a zener diode 54. The supply voltage circuit 46 corresponds in its functionality to a power supply unit. With the supply voltage circuit 46, the high voltage U _B , which may be in the range of 250 to 450 volts, be converted into a supply voltage U _v , which is for example of the order of about 15 volts. The supply voltage should in any case be so large that the switch elements T1, T2, T3, T4, T5, T6, in particular the switch elements T2, T4, T6 can be safely and reliably actuated to realize the short circuit of the phases 20, 22, 24 , in which connection voltage losses occurring in intermediate components are to be taken into account.

The realization of the supply voltage circuit 46 as a series shading of an electrical resistance and a Zener diode has the advantage that by means of such a supply voltage circuit, a passive discharge of the DC link capacitance is possible, the value of the resistor determines the length of time it takes for the at the DC link capacitance voltage under one of the

Berührschutzgrenze defined voltage value has fallen or until a complete discharge of the DC link capacity has occurred.

The supply voltage circuit 46 is a stabilizing circuit 56 downstream. The stabilization circuit 56 ensures that a sufficiently large current for the short-circuiting of the phases 20, 22, 24 of the electric machine 18 required driving the Schalterele- T1, T2, T3, T4, T5, T6 of the inverter 28, in particular the switch elements T2, T4, T6 can be provided. As can be seen from the illustration in FIG. 2, the stabilization circuit 56 consists of a transistor 58 whose base is supplied with the supply voltage Uv. The collector of the transistor 58 is connected via an electrical resistor 60 to the input voltage U _E. The emitter is connected to ground via a parallel circuit formed by a Zener diode 62 and an electrical resistor 64.

As can be seen from the illustration in FIG. 2, the stabilization circuit 56 is arranged in terms of circuitry between the supply voltage circuit 46 and an activation element 66. The activation element 66 is designed to close an activation path 70 in the presence of a switch-on condition, which is indicated by a directional arrow 68, in order to activate a discharge circuit 72 and a short-circuit control circuit 74 by providing the supply voltage U _V. That is, in the presence of a switch-on condition 68, the activation path 70 is closed, via which the discharge circuit 72 and the short-circuit control circuit 74 are then supplied with the supply voltage U _V provided by the supply voltage circuit 46 and thus activated. In this respect, one can also call this path a supply path. The activation element 66 may be a drivable semiconductor element or a relay.

As already mentioned above, by means of the supply voltage circuit 46, a passive discharge of the DC link capacitance 16 is possible. In contrast, by means of the discharge circuit 72, an active discharge of the DC link capacitance 16.

It is stated above that in the presence of a switch-on condition 68, the discharge circuit 72 and the short-circuit control circuit 74 are connected to the supply voltage provided by the supply voltage circuit 46. U _{V be} supplied. This is to be understood that in the presence of the switch-on condition 68, the activation path 70 is closed and thus a technical or circuit connection of the

Discharge circuit 72 and the short-circuit control circuit 74 to the supply voltage U _V consists. Of course, the voltage value of the supply voltage U _V itself is not available for activating the two circuits, but the reduced voltage value of the stabilizing voltage U _S provided by the stabilizing circuit 56 is available.

Preferably, the electric drive unit 10 should be arranged in a vehicle, not shown. Consequently, the power-on condition 68 is given when at least one of the following situations exists:

Transferring the vehicle from a driving state to a resting state or

- shut down the traction battery, or

The evaluation of the aforementioned situations and the provision of a signal representing the switch-on condition takes place in the already described arithmetic unit 42, from which this signal is output via a terminal 76.

The short-circuit control circuit 74 is configured to short-circuit at least a portion of the phases 20, 22, 24 of the electric machine 18 in its activated operating state by activating part of the switching elements T1, T2, T3, T4, T5, T6. Preferably, all phases 20, 22, 24 are short-circuited. For this purpose, the short circuit control circuit 74 includes diodes which are connectable to the control terminals of the switching elements T2, T4, T6 with their Ansteueranschlüssen. In the case of the IGBTs shown in FIG with their gates. In FIG. 2, one of these diodes is designated by the reference numeral 78 by way of example.

As already stated, it is sufficient for short-circuiting the phases 20, 22, 24, the Schatterelemente T2, T4, T6 to turn on, whereas the switch elements T1, T3, T5 can remain in the blocking state. This means that control signals Bi are to be provided only for the switch elements T2, T4, T6, for which reason the short-circuit control circuit 74 shown in FIG. 2 has only three diodes 78.

In the safety circuit arrangement 12 according to the invention, it is provided that the shorting control circuit 74 controls the second switching elements 34 connected to the grounding pole 38. The second switch elements 34 are thereby turned on. Preferably, all three second peeling elements 34 are turned on, so that the phases 20, 22, 24 are all short-circuited with each other. The control of the second switch elements described here is not intended to have a limiting effect. Likewise, the phases of the electric machine can also be short-circuited by driving the first peeling elements.

The discharge circuit 72 is designed to remove a predefinable discharge current in its activated operating state of the intermediate circuit capacitor 16. Thus, in addition to the passive discharge of the DC link 16; which is realized by the supply voltage circuit 46, if necessary, i. Upon activation of the discharge circuit 72 and an active discharge of the DC link 16 possible.

As can be seen from the illustration in FIG. 2, the discharge circuit 72 is a series circuit consisting of an electrical load resistor 80 and a controllable semiconductor element 82. Preferably, the semiconductor element 82 may be a MOSFET, as shown in FIG. The load resistor 80 and the Semiconductor elements 82 are dimensioned or designed so that the intermediate circuit capacitance 16 can be discharged in a very short time, at least to the extent that the voltage applied to it is below the contact protection limit of 60 volts. For example, the

Discharge circuit 72 be set so that this level is reached within 5 seconds.

As can also be seen from the illustration in FIG. 2, the safety circuit arrangement 12 furthermore has a monitoring circuit 84, which is designed to process an electrical signal representing a temperature present at the load resistor 80. Depending on the determined monitoring result then the semiconductor element 82 can be controlled. Thus, overheating and, as a result, potential damage or even destruction of the load resistor 80 can be prevented by the discharge current being able to be set as a function of the load resistance temperature. Preferably, the discharge current is reduced with increasing temperature, which can go so far that when a predetermined temperature threshold value is exceeded

Discharge current is reduced to 0, i. the discharge of the DC link capacity 16 is interrupted at least temporarily.

As can be seen from the illustration in FIG. 2, the monitoring circuit 84 contains a measuring bridge circuit 86, which is constructed from electrical measuring resistors, one of which is denoted by the reference numeral 88 by way of example. One of the measuring resistors is a temperature-dependent resistor 90, which preferably has a negative temperature coefficient. The temperature-dependent resistor 90 is structurally arranged in the immediate vicinity of the load resistor 80. By means of a comparator 92, a drive signal for the semiconductor element 82 is generated. 3 shows, by way of a circuit diagram, an exemplary structure of a superposition circuit arrangement 94 contained in the drive unit 26. The superimposed circuit arrangement 94 has three superposition modules, each of which is assigned to one of the switch elements T2, T4, T6, by means of which the shorting of the Phases 20, 22, 24 should take place. Of the three overlay modules, one is designated by reference numeral 96 by way of example. The following statements thus relate to the overlay module marked in this way, but apply equally to the other two overlay modules.

As already stated, the overmodulation module 96 essentially has the following two functionalities to fulfill: on the one hand, the duty cycle values d _{i are} to be converted into drive signals A _i . On the other hand, the drive signals Bi are superimposed on the drive signals Ai. The conversion of the duty cycle values d _i into the drive signals A takes place by means of a series circuit composed of a driver 98 and a resistor 100. The superposing takes place by means of a diode 102

The conversion unit contained in the drive unit and associated with the three other switch elements T1, T3, T5, which in each case contains a series circuit composed of a driver and a resistor for each of the three switch elements, is not shown in FIG. 3 for reasons of clarity. Since the short circuiting of the phases 20, 22, 24 is to take place by means of the three switch elements T2, T4, T6, only the functionality of the conversion is needed for the three switch elements T1, T3, T5, the functionality of the overlay is not needed. Accordingly, there are no drive signals Bi for the switch elements T1, T3, T5.

Characterized in that the safety circuit arrangement according to the invention comprises a supply voltage circuit which, starting from the DC link voltage supplied to it, supplies a supply voltage for the DC link voltage Discharge circuit and the short-circuit control circuit provides, it is also in case of simultaneous failure or not available the

Traction battery and the starter battery possible to realize an active discharge of the DC link capacity and an active short circuit of the terminals or phases of the electric machine.

At this point, it should be noted that the reference made in the above-described embodiment to an electric drive unit disposed in a vehicle is not intended to have any restrictive effect. The safety arrangement according to the invention can also be used in other electrical drive units used.

List of Reference Numerals 10 Electric drive unit

12 safety arrangement

14 traction battery

16 DC link capacity

18 electric machine

20 phase

22 phase

24 phase

26 control unit

28 inverters

30 half bridge

32 first switch element

34 second switch element

36 supply pole

38 ground pole

40 freewheeling diode

42 arithmetic unit

44 interruption

46 Supply voltage circuit 48 Terminal

50 clamp

52 electrical supply resistor 54 Zener diode

56 stabilization circuit

58 transistor

60 electrical resistance

62 zener diode

64 electrical resistance

66 activation element

68 Peil 70 Activation path 72 Discharge circuit

74 Short circuit control circuit 76 Terminal

78 diode

80 electrical load resistance

82 controllable semiconductor element 84 monitoring circuit

86 measuring bridge circuit

88 measuring resistor

90 temperature dependent resistor 92 comparator

94 Overlay circuitry 96 Overlay module

98 drivers

100 resistance

102 diode

Claims

claims

A safety circuit arrangement for an electric drive unit, wherein the electric drive unit has a traction battery, an intermediate circuit capacitor connected in parallel to the traction battery and an electrical machine that can be supplied with electrical energy by the traction battery, wherein the electrical machine has a plurality of phases which can be controlled via a a plurality of switch elements having inverter with the Traktjonsbatterie are connectable with

a discharge circuit, which is designed to remove a predefinable discharge current in its activated operating state of the DC link capacitance,

a short-circuit control circuit, which is designed to short-circuit at least part of the phases of the electrical machine in its activated operating state by driving a part of the switching elements,

a supply voltage circuit, which is designed to provide a supply voltage starting from an input voltage supplied to it, wherein an intermediate circuit voltage applied to the intermediate circuit capacitance is supplied as input voltage, and

an activation element, which is configured to close an activation path in the presence of a switch-on condition in order to activate the discharge circuit and the short-circuit control circuit by providing the supply voltage.

2. Safety circuit arrangement according to claim 1, characterized in that the electric drive unit in a vehicle is ordered and the switch-on condition is given if at least one of the following situations exists:

Transferring the vehicle from a driving state to a resting state or

- shut down the traction battery, or

3. Safety circuit arrangement according to one of the preceding claims, characterized in that it is in the supply voltage Schaitung consisting of an electrical supply resistor and a Zener diode series circuit.

4. Safety circuit arrangement according to one of the preceding claims, characterized in that it is in the

Discharge circuit is a consisting of an electrical load resistor and a controllable semiconductor element series circuit.

5. Safety circuit arrangement according to one of the preceding claims, characterized in that the safety circuit arrangement further comprises a monitoring circuit, wherein the monitoring circuit is adapted to process an electrical signal representing a temperature present at the load resistor.

6. Safety circuit arrangement according to claim 5, characterized in that the monitoring circuit is designed to control the controllable semiconductor element as a function of a determined monitoring result,

7. Safety circuit arrangement according to claim 5 or 6, characterized in that the monitoring circuit comprises a constructed of electrical measuring resistors measuring bridge circuit, wherein one of the measuring resistors is designed as a temperature-dependent resistor.

8. Safety circuit arrangement according to claim 7, characterized in that the temperature-dependent resistor has a negative temperature coefficient.

9. Safety circuit arrangement according to one of the preceding claims, characterized in that the safety circuit arrangement further comprises a stabilization circuit, which is arranged in terms of circuitry between the supply voltage circuit and the activation element.

10. Safety circuit arrangement according to one of the preceding claims, characterized in that the inverter has a plurality of half-bridges, each half-bridge having a first and a second switch element, wherein the first switch element with a supply pole of the traction battery and the second switch element with a ground pole of the traction battery is connected, wherein the short circuit control circuit is adapted to drive the connected to the ground pole second switch elements.