Method and device for transferring the electric drive of a vehicle into a safe state

Abstract

The invention relates to a device for transferring the drive of a vehicle into a safe operating state, wherein the drive comprises an electric machine, in particular a synchronous machine, which is operated with electrical energy from an electrical energy store via an intermediate circuit and an inverter. The device is designed to determine, on the basis of an intermediate circuit voltage of the intermediate circuit, that a transfer procedure is to be carried out in order to transfer the drive into the safe operating state and, in response thereto, to bring about a freewheeling operation of the inverter in a freewheeling phase of the transfer procedure. The device is also designed to determine, on the basis of the intermediate circuit voltage, that the freewheeling operation of the inverter is to be ended and, in response thereto, to bring about a short-circuit operation of the inverter in a short-circuit phase of the transfer procedure, which short-circuit phase follows the freewheeling phase.

Description

[0001] Method and device for transferring the electric drive of a

[0002] Vehicle in a safe condition

[0003] The invention relates to a method and a corresponding device, each of which is configured to bring an electric machine, in particular a current-excited synchronous machine, of an electric drive of a vehicle into a safe operating state.

[0004] An electrically powered vehicle has at least one electric drive motor, which may be designed as a current-excited synchronous motor. During operation of the drive motor, a situation may arise in which the electric drive motor must be brought into a safe operating state.

[0005] This document deals with the technical task of transitioning an electrical machine, in particular a current-excited synchronous machine, into a safe operating state in a particularly reliable, efficient and gentle manner.

[0006] The problem is solved by each of the independent claims. Advantageous embodiments are described, inter alia, in the dependent claims. It should be noted that additional features of a claim dependent on an independent claim, without the features of the independent claim itself or only in combination with a subset of the features of the independent claim, can constitute a separate invention independent of the combination of all features of the independent claim, which can be made the subject of an independent claim, a divisional application, or a subsequent application. This applies equally to technical teachings described in the description, which can constitute an invention independent of the features of the independent claims.

[0007] According to one aspect, a device for transitioning the (electric) drive of a (motor) vehicle into a safe operating state is described. The drive comprises an electric machine (for driving the vehicle), in particular a synchronous machine, which is operated via a DC link and an inverter with electrical energy from an electrical (in particular an electrochemical) energy storage device. The DC link typically includes a DC link capacitor with one or more DC link capacitors.

[0008] The inverter can be configured to generate a multi-phase AC voltage for operating the electric machine based on the DC link voltage (i.e., based on a DC voltage). The DC link voltage can correspond to the voltage across the DC link capacitor. The inverter can include several switching elements (especially high-side and low-side switching elements) to generate the AC voltage.

[0009] The electric machine can be a current-excited electric machine, powered via the DC link and an additional excitation circuit (with a DC-DC converter) for the rotor using electrical energy from the electrical energy storage device. The excitation circuit can comprise one or more switching elements to generate the excitation voltage (i.e., a DC voltage) for the rotor windings.

[0010] The drive can include a disconnect switching element designed to electrically couple the energy storage device to the intermediate circuit in the switched-on state and to decouple the energy storage device from the intermediate circuit in the switched-off state.

[0011] The device is configured to determine, based on the DC link voltage, that a transition procedure must be performed to bring the drive into a safe operating state. The device can, in particular, be configured to determine that the transition procedure must be performed based on the value of the DC link voltage and / or on the gradient of the time-dependent DC link voltage. For example, it can be determined that the transition procedure must be performed if, and especially as soon as,

[0012] • the DC link voltage is equal to or greater than a first voltage threshold, where the first voltage threshold is typically greater (e.g., by 5% or more) than the nominal voltage of the energy storage device; and / or

[0013] • the gradient of the time course of the intermediate circuit voltage is equal to or greater than a gradient threshold value.

[0014] Alternatively or additionally, the device can be configured to detect, based on the DC link voltage (e.g., by comparison with the first voltage threshold and / or by comparison with the gradient threshold), that the disconnecting switching element is in the off state and that the electric machine is generating electrical energy, in particular recuperating it. It can then be determined, in response to this detection, that the transition procedure is to be carried out.

[0015] The device is further configured to initiate freewheeling operation of the inverter during a freewheeling phase of the transition procedure, in response to the stipulation that the transition procedure is to be performed. For freewheeling operation, the switching elements, in particular all switching elements, of the inverter can be switched off (permanently and / or for the entire freewheeling phase). Furthermore, during the freewheeling phase of the transition procedure, the excitation circuit can be operated in freewheeling mode, in which one or more switching elements, in particular all switching elements, of the excitation circuit are switched off (permanently and / or for the entire freewheeling phase).

[0016] Furthermore, the device is configured to determine, based on the DC link voltage, that the inverter's freewheeling operation must be terminated. The device can be configured, in particular, to determine that the inverter's freewheeling operation must be terminated when, and especially as soon as, the DC link voltage is equal to or greater than a second voltage threshold (where the second voltage threshold is greater, e.g., by 10% or more, than the first voltage threshold). The second voltage threshold is preferably equal to or less than the maximum permissible operating voltage of the DC link. The second voltage threshold can, for example, be at most 10% below the maximum permissible operating voltage.

[0017] During the freewheeling phase, energy can be transferred from the inductors of the electric machine to the DC link and stored there (until the DC link voltage reaches the second voltage threshold). The device is further configured, in response to the determination that freewheeling operation must end (because the DC link voltage has reached the second voltage threshold, and thus no further energy can be absorbed in the DC link), to induce short-circuit operation of the inverter in a short-circuit phase of the transition procedure directly following the freewheeling phase. For short-circuit operation, the switching elements can be energized (permanently and / or throughout the entire short-circuit phase) to create a short circuit of the different (in particular, all) phases of the electric machine.Furthermore, during the short-circuit phase of the transition procedure, the excitation circuit can be operated in a short-circuit mode in which one or more switching elements, in particular all switching elements, of the excitation circuit are switched on (permanently and / or during the entire short-circuit phase).

[0018] During the short-circuit phase, the remaining energy in the inductors of the electric machine (which remained after the freewheeling phase) can be dissipated via the electrical resistances of the drive. Because some of the energy was already dissipated during the freewheeling phase (and the excitation current was reduced), relatively low transient currents occur during the short-circuit phase, resulting in a particularly smooth transition to safe operation.

[0019] The device can be configured to reduce the DC link voltage and / or at least partially discharge the DC link in a phase of the transition procedure directly following the short-circuit phase by operating the inverter. This provides a particularly safe transition procedure. The transition procedure preferably has only exactly one freewheeling phase and only exactly one directly following short-circuit phase to ensure a particularly efficient transition to the safe operating state.

[0020] According to another aspect, a (road) motor vehicle (in particular a passenger car or a truck or a bus or a motorcycle) is described that includes the device described in this document.

[0021] According to one aspect, a method for transitioning the (electric) drive of a vehicle into a safe operating state is described. The drive comprises an electric (drive) machine, in particular a synchronous machine, which is operated via a DC link and an inverter with electrical energy from an electrical energy storage device (e.g., also a high-voltage battery, e.g., with a nominal voltage of 300V or more).

[0022] The procedure includes determining, based on the DC link voltage, that a transition procedure is to be carried out in order to bring the drive into a safe operating state, and in response to determining that the transition procedure is to be carried out, causing the freewheeling operation of the inverter in a freewheeling phase of the transition procedure.

[0023] Furthermore, the method comprises determining, based on the intermediate circuit voltage, that the freewheeling operation of the inverter is to be terminated, and, in response to this determination, initiating short-circuit operation of the inverter in a subsequent short-circuit phase of the transition procedure. It should be noted that the aspects described in connection with the device, in particular the claims described in connection with the device, are also applicable to the method as corresponding method features.

[0024] Another aspect described is a software (SW) program. The SW program can be configured to run on a processor (e.g., on a vehicle's control unit) and thereby execute the procedure described in this document.

[0025] Another aspect describes a storage medium. This storage medium can include a software program configured to run on a processor and thereby execute the procedure described in this document.

[0026] It should be noted that the methods, devices, and systems described in this document can be used both alone and in combination with other methods, devices, and systems described in this document. Furthermore, any aspect of the methods, devices, and systems described in this document can be combined with one another in a variety of ways. In particular, the features of the claims can be combined with one another in a variety of ways. Features listed in parentheses are to be understood as optional features.

[0027] The invention will now be described in more detail using exemplary embodiments.

[0028] Figure 1a shows exemplary components of a vehicle with an electric drive motor;

[0029] Figure 1b shows an exemplary inverter and an exemplary excitation circuit for providing the excitation current for an electric machine of a vehicle; Figure 1c shows the exemplary excitation circuit for providing the excitation current for the rotor of an electric machine;

[0030] Figure 2a shows an exemplary time course of the intermediate circuit voltage; Figure 2b shows exemplary current and voltage curves during the transition of an electrical machine to a safe operating state; and

[0031] Figure 3 shows a flowchart of an exemplary procedure for bringing an electrical machine into a safe operating state.

[0032] As stated at the outset, this document deals with the reliable, gentle, and efficient transition of a (current-excited) electric machine into a safe operating state. In this context, Fig. 1a shows exemplary components of a vehicle 140, which has an electric machine 103 for driving the vehicle 140. The electric machine 103 is coupled to one or more wheels 141 of the vehicle 140 in order to drive the one or more wheels 141 and thus the vehicle 140. The electric machine 103 is operated with electrical energy from an electrical, in particular an electrochemical, energy storage device 130. The energy storage device 130 can be configured to provide a direct current with a specific direct voltage (e.g., of 300 V or more).

[0033] The vehicle 140 has an inverter 100, which is configured to generate phase currents for the different phases of the electric machine 103 based on the direct current from the energy storage device 130. The inverter 100 can be operated by a (control) device 101. The inverter 100 and the electric machine can be part of the electric drive or the electric drive system of a vehicle 140.

[0034] Fig. 1b shows an exemplary inverter 100, which is set up to

[0035] Basis of an intermediate circuit voltage 110 (i.e., a DC voltage)

[0036] to generate phase voltages 111 (i.e., alternating voltages) for the inductors of the electric machine 103. The drive may further have an intermediate circuit 105 with an intermediate circuit capacitor, to which the

[0037] The intermediate circuit voltage is 110.

[0038] The inverter 100 comprises several switching elements 102, 104, which in the illustrated example are arranged in a half-bridge for each phase 121, 122, 123. The switching elements 102, 104 are controlled by the (control) device 101 to generate the phase voltages 111 for the electric machine 103. The individual phase currents 112 and / or phase voltages 111 can be supplied to the electric machine 103 via corresponding phase lines.

[0039] The electric machine 103 can have a current-excited rotor, wherein the rotor has rotor windings through which a rotor inductance 151 is formed (as illustrated by way of example in Figures 1b and 1c). An electric excitation current 162 (in particular a direct current) can flow through the rotor inductance 151, so that a magnetic field (or a magnetic flux) is generated through the rotor inductance 151, upon which the rotating field generated by the stator acts to drive the rotor.

[0040] The excitation current 162 for the rotor inductance 151 can be supplied to the rotor via slip rings 152, the (rotating) slip rings 152 being in contact with (stationary) brushes 153. An excitation voltage 161 (in particular a DC voltage) can be applied to the brushes 153, causing the excitation current 162. The magnitude of the excitation voltage 161 can be set by a DC-DC converter 154, which is configured to generate the excitation voltage 161 from a supply voltage 160 (where the supply voltage 160 can correspond to the intermediate circuit voltage 110). The magnitude of the excitation current 162 can be adjusted by the magnitude of the excitation voltage 161, e.g., using current control. The torque provided by the electric machine 103 typically increases with increasing magnitude of the excitation current 162.

[0041] During operation of the electric machine 103, it may happen (e.g., due to a defect) that the isolating switching element 170, via which the intermediate circuit 105 is coupled to the electrical energy storage device 130, is open, and as a consequence, the electrical energy storage device 130 is disconnected from the inverter 100. This, in turn, may prevent the electric machine 103 from being supplied with electrical energy from the energy storage device 130 to power the vehicle 140. The electric machine 103 should then be brought into a safe operating state. The safe operating state may have one or more operating conditions, in particular,

[0042] • an operating condition such that the phase voltages 111 and / or the excitation voltage 161 are each less than a predefined voltage threshold (e.g. 60V or less); and / or

[0043] • an operating condition such that the phase currents 112 and / or the excitation current 162 are each less than a predefined current threshold (e.g. 1 A or less); and / or

[0044] • an operating condition such that the torque generated by the electric machine 103 is less than a predefined torque threshold.

[0045] The electrical energy stored in the inductors 151 of the electric machine 103 can be dissipated by short-circuit operation, in particular by an active short circuit (ACS). During short-circuit operation, all high-side switching elements 102 (or alternatively all low-side switching elements 104) of the inverter 100 and the DC-DC converter 154 can be permanently closed (to cause a short circuit of the different phases and a short circuit of the rotor inductor 151). This can lead to relatively high transient currents, especially if a relatively large amount of energy is still stored in the inductors 151 of the electric machine 103.

[0046] Another way to dissipate the energy stored in the inductors 151 of the electric machine 103 is freewheeling operation, in which the switching elements 102, 104 of the inverter 100 and the DC-DC converter 154 are permanently open. Currents then flow through the freewheeling diodes of the switching elements 102, 104 to the DC link 105, in particular to the DC link capacitor, and to the energy storage device 130. The energy from the inductors 151 of the electric machine 103 can thus be transferred to the DC link capacitor and / or to the energy storage device 130.

[0047] As explained above, the isolating switching element 170 between the DC link capacitor and the energy storage device 130 may become open (particularly due to a defect). As a consequence, the energy from the inductors of the electric machine 103 and / or the electrical energy generated during a recuperation phase of the electric machine 103 cannot be directed to and stored in the energy storage device 130. This results in an increase in the DC link voltage 110 across the DC link capacitor, which can impair the DC link capacitance if the DC link voltage 110 exceeds a certain maximum permissible value.

[0048] The device 101 can be configured to detect a situation in which the disconnect switching element 170 is open during operation of the electric machine 103, in particular during a recuperation phase of the electric machine 103. Such a situation can be detected based on the intermediate circuit voltage 110, in particular based on the value and / or on the gradient of the time course of the

[0049] DC link voltage 110.

[0050] Fig. 2a shows an exemplary time course 220 of the DC link voltage 110. The DC link voltage 110 typically has a specific nominal value 200 (the nominal voltage of the energy storage device 130). In the example shown in Fig. 2a, at a first time point 211, a situation arises in which the isolating switching element 170 is opened and the electric machine 103 is in a recuperation phase. As a result, the DC link voltage 110 increases. The time course 220 of the DC link voltage 110 then exhibits a specific time gradient 221 (with which the DC link voltage 110 increases).

[0051] Based on the DC link voltage 110, and in particular on the time course 220 of the DC link voltage 110, it can be determined that the electrical machine 103 (due to a defect in the isolating switching element 170) must be brought into a safe operating state. In response, a transition procedure can be initiated by which the electrical machine 103 is brought into the safe operating state. In the example shown in Fig. 2a, the transition procedure is initiated at a second time point 212.

[0052] The device 101 can be configured to compare the DC link voltage 110 with a first voltage threshold 201 to determine whether the electrical machine 103 should be switched to the safe operating state. For example, it can be determined that the electrical machine 103 should be switched to the safe operating state when (in particular as soon as) it is detected that the DC link voltage 110 is equal to or greater than the first voltage threshold 201. Alternatively or additionally, the gradient 221 of the time course 220 of the DC link voltage 110 can be compared with a gradient threshold to determine whether the electrical machine 103 should be switched to the safe operating state.For example, it can be determined that the electrical machine 103 is to be brought into the safe operating state when (in particular as soon as) it is recognized that the gradient 221 is (in magnitude) equal to or greater than the gradient threshold.

[0053] The transition procedure initially comprises a freewheeling phase, during which the inverter 100 and the DC-DC converter 154 operate in freewheeling mode. As a result, electrical energy stored in the inductors 151 of the electric machine 103 is transferred to the DC link capacitance and stored there. This causes the DC link voltage 110 to rise further, as illustrated by example in Fig. 2a.

[0054] The transition procedure includes a short-circuit phase immediately following the freewheeling phase, during which the inverter 100 and the DC-DC converter 154 operate in short-circuit mode. Because the amount of electrical energy stored in the inductors 151 of the electric machine 103 was reduced during the freewheeling phase, the transient currents resulting from the short-circuit operation are reduced.

[0055] In particular, a sufficiently long free-running phase can ensure that the transient currents caused during the short-circuit phase do not exceed a predefined maximum value.

[0056] The device 101 can be configured to effect the transition from the free-running phase to the short-circuit phase depending on the DC link voltage 110. In particular, the transition from the free-running phase to the short-circuit phase can be effected when (especially as soon as) the DC link voltage 110 is equal to or greater than a second voltage threshold 202 (which is greater than the first voltage threshold 201).

[0057] During the short-circuit phase, the amount of electrical energy remaining in the inductors of the electrical machine 103 is further reduced until the safe operating state of the electrical machine 103 is reached.

[0058] Fig. 2b shows exemplary time courses of measured quantities during the transfer procedure, in particular

[0059] • the temporal course 231 of the excitation stream 162;

[0060] • the temporal course 232 of the phase currents 112;

[0061] • the time course 233 of the phase voltages 111; and

[0062] • the temporal course 234 of the electric current.

[0063] A method is thus described by which the maximum DC bus voltage (i.e., the intermediate circuit voltage) 110 is limited, by which all components 105, 100, 103, 154 of the drive of a vehicle 140 are protected from overvoltage, and by which a smooth transition to the safe (operating) state is effected.

[0064] In the first step of the procedure, it is detected that the main switch (i.e., the disconnect switching element 170) is off (e.g., due to a failure in the control system) and that the vehicle's drive 140 is in recuperation mode. In this case, the voltage 110 measured at the DC link capacitor 105 is increased. This detection can be carried out by checking the absolute value of the voltage 110 and / or by checking the gradient 221 of the time course 220 of the voltage 110.

[0065] In a second step, all switching elements 102, 104 can be (permanently) switched off. The inverter 100 and the excitation circuit (i.e., the DC-DC converter) 154 are then each in freewheeling operation. The energy stored in the inductors 151 flows into the DC link capacitor. An immediate switch to short circuit (i.e., active short circuit, ASC) at the beginning of the transition procedure could cause excessive transient currents that could damage the (semiconductor-based) switching elements 102, 104. These transient currents are defined by the magnetic flux in the electric machine 103, with the magnetic flux typically controlled by the rotor current 162. Freewheeling operation allows the rotor current 162 (i.e., the excitation current) to be reduced, thereby reducing the transient currents during the subsequent short-circuit operation.The capacitor in the intermediate circuit 105 can absorb the energy from the electric machine 103 until a certain (second) voltage threshold 202 is reached.

[0066] The rotor current 162, or the magnetic flux in the electric machine 103, is reduced during freewheeling operation to such an extent that it is subsequently possible to switch to short-circuit operation. The transient currents are then so low that damage to the components in the inverter 110 and / or in the excitation circuit 154 can be avoided. During short-circuit operation, the energy does not flow into the DC link capacitor, but is dissipated in the resistances of the drive system.

[0067] Optionally, the DC link capacitance can be at least partially discharged to reduce the DC link voltage 110. This can be achieved by dedicated operation of the inverter 110 (in which a specific E-current is set for the stator current without causing any torque on the shaft of the electric machine 103).

[0068] Fig. 2b shows measured values ​​during the transition procedure. The drive is initially in recuperation mode (with a negative E-current, charging the energy storage 130). At time 212, the increase in the DC link voltage 110 is detected, and the system switches to freewheeling operation. The motor currents 112 then drop to zero, and the rotor current 162 decreases. At time 213, the rotor current 162 is significantly reduced, and the system switches to short-circuit operation. This results in transient currents, which, however, are so low that damage to the holding conductor shielding elements 102, 104 can be avoided.

[0069] Fig. 3 shows a flowchart of a (possibly computer-implemented) method 300 for transitioning the drive of a (motor) vehicle 140 into a safe operating state (in which the electric machine of the drive is essentially free of current, voltage, and / or torque). The drive comprises an electric machine 103, in particular a synchronous machine, which is operated via a DC link 105 (with a DC link capacitance) and an inverter 110 with electrical energy from an electrical (in particular an electrochemical) energy storage device 130. The method 300 can be implemented by a control device 101.

[0070] Method 300 comprises determining, based on the DC link voltage 110 of the DC link 105, that a transition procedure (which can also be referred to as a transfer procedure) must be carried out to bring the drive into a safe operating state. In particular, it can be determined that the DC link voltage 110 reaches or exceeds a certain voltage threshold value 201.

[0071] Method 300 further comprises, in response to the determination 301 that the transition procedure is to be carried out, the initiation 302 of freewheeling operation of the inverter 110 during a freewheeling phase of the transition procedure (in which all switching elements 102, 104 of the inverter 110 are switched off (and current flows only through the freewheeling diodes of the switching elements 102, 104)). Method 300 also comprises determining 303, based on the DC link voltage 110, that the freewheeling operation of the inverter 110 is to be terminated (e.g., because the DC link voltage 110 reaches or exceeds a certain voltage threshold 202).

[0072] The procedure 300 also includes, in response to the determination 303 that the freewheeling operation of the inverter 110 is to be terminated, the effect 304, in a short-circuit phase of the transition procedure following the freewheeling phase, of the short-circuiting operation of the inverter 110 (in which, for example, all high-side switching elements 102 or all low-side switching elements 104 are activated; and / or in which all phases of the electrical machine 103 are short-circuited).

[0073] The measures described in this document enable an electric machine 103, in particular a recuperative electric machine 103, to be brought into a safe operating state in a reliable, efficient and gentle manner.

[0074] The present invention is not limited to the embodiments shown. In particular, it should be noted that the description and the figures are intended only to illustrate the principle of the proposed methods, devices, and systems by way of example.

Claims

Claims 1) Device (101) for bringing a drive of a vehicle (140) into a safe operating state; wherein the drive comprises an electric machine (103), in particular a synchronous machine, which is operated via an intermediate circuit (105) and an inverter (110) with electrical energy from an electrical energy storage device (130); wherein the device (101) is configured, - to determine, based on an intermediate circuit voltage (110) of the intermediate circuit (105), that a transition procedure must be carried out in order to bring the drive into the safe operating state; - in response to this, to cause free-running operation of the inverter (110) during a free-running phase of the transition procedure; - to determine, based on the intermediate circuit voltage (110), that the freewheeling operation of the inverter (110) is to be terminated; and - in response to this, to cause short-circuit operation of the inverter (110) in a short-circuit phase of the transition procedure following the free-running phase. 2) Device (101) according to claim 1, wherein the device (101) is configured to determine, on the basis of a value of the intermediate circuit voltage (110) and / or on the basis of a gradient (221) of a time course (220) of the intermediate circuit voltage (110), that the transition procedure is to be carried out. 3) Device (101) according to claim 2, wherein the device (101) is configured to determine that the transfer procedure is to be carried out when, in particular as soon as, - the intermediate circuit voltage (110) is equal to or greater than a first voltage threshold (201); where the first voltage- Threshold (201) in particular is greater than a nominal voltage of the energy storage device (110); and / or - the gradient (221) of the time course (220) of the intermediate circuit voltage (110) is equal to or greater than a gradient threshold. 4) Device (101) according to one of the preceding claims, wherein - the device (101) is configured to determine that the freewheeling operation of the inverter (110) is to be terminated when, in particular as soon as, the intermediate circuit voltage (110) is equal to or greater than a second voltage threshold value; and - the second voltage threshold is in particular equal to or less than a maximum permissible operating voltage of the intermediate circuit (105). 5) Device (101) according to one of the preceding claims, wherein - the electric machine (103) is a current-excited electric machine which is operated via the intermediate circuit (105) and via an additional excitation circuit (162) for a rotor of the electric machine (103) with electrical energy from the electrical energy storage device (130); - the device (101) is set up, - to operate the excitation circuit (162) in a freewheeling mode during the freewheeling phase of the transition procedure, in which one or more switching elements, in particular all switching elements, of the excitation circuit (162) are switched off; and - to operate the excitation circuit (162) in a short-circuit mode during the short-circuit phase of the transition procedure, in which one or more switching elements, in particular all switching elements, of the excitation circuit (162) are switched on. 6) Device (101) according to one of the preceding claims, wherein the device (101) is configured to cause the intermediate circuit voltage (110) to be reduced and / or the intermediate circuit (105) to be at least partially discharged in a phase of the transition procedure following the short-circuit phase by operating the inverter (100). 7) Device (101) according to one of the preceding claims, wherein - the inverter (110) comprises switching elements (102, 104); and - the device (101) is set up, - to ensure that the switching elements (102, 104), in particular all switching elements (102, 104), of the inverter (110) are switched off for freewheeling operation; and - to cause the switching elements (102, 104) to be switched on for short-circuit operation in order to cause a short circuit of different phases of the electrical machine (103). 8) Device (101) according to one of the preceding claims, wherein - the intermediate circuit (105) comprises an intermediate circuit capacitance with one or more intermediate circuit capacitors; and - the intermediate circuit voltage (110) corresponds to the voltage across the intermediate circuit capacitance. 9) Device (101) according to one of the preceding claims, wherein - the drive comprises a disconnect switching element (170) configured to electrically couple the energy storage device (130) to the intermediate circuit (105) in a switched-on state and to decouple the energy storage device (130) from the intermediate circuit (105) in a switched-off state; and - the device (101) is set up, - to recognize, based on the intermediate circuit voltage (110), that the disconnect switching element (107) is in the switched-off state, and that the electric machine (103) is generating electrical energy, in particular recuperating it; and - to determine, in response to the recognition that the transition procedure is to be carried out. 10) Method (300) for bringing a vehicle drive (140) into a safe operating state; wherein the drive comprises an electric machine (103), in particular a synchronous machine, which is operated via an intermediate circuit (105) and an inverter (110) with electrical energy from an electrical energy storage device (130); wherein the method (300) comprises, - Determine (301), based on an intermediate circuit voltage (110) of the intermediate circuit (105), that a transition procedure must be carried out to bring the drive into the safe operating state; - in response to the determination (301) that the transfer procedure is to be carried out, effect (302) a free-running phase of the transfer procedure, a free-running operation of the inverter (HO); - Determine (303), based on the intermediate circuit voltage (110), that the freewheeling operation of the inverter (110) is to be terminated; and - in response to the determination (303) that the free-running operation of the inverter (110) is to be terminated, effect (304) a short-circuit phase of the transition procedure following the free-running phase, of a short-circuit operation of the inverter (110).

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