Method for controlling operation of electric machine

Abstract

The invention relates to a method for controlling the operation of an electric machine, in particular of a motor vehicle, in the event of a fault, comprising the following steps: detecting a current current vector (6) of the electric machine; -determining a varying voltage vector (12) as a function of the detected current vector (6); changing the current operating point (15, 15 ') of the electric machine to a changed operating point (16, 16') by setting the changing voltage vector (12), the power resulting from the change of the operating point (15, 15 ') being equal to or less than the power loss, in particular the thermal power loss, of the electric machine, and carrying out the active short-circuit state starting from the changed operating point (16, 16').

Description

Technical Field

[0001] The invention relates to a method for controlling the operation of an electric machine, in particular of a motor vehicle, in the event of a fault. Background Art

[0002] Methods for controlling the operation of electric motors, particularly for motor vehicles, in the event of a fault are generally known in the prior art. For example, it is known that if a fault occurs, the electric motor or a drive device including the electric motor should be brought into a safe state. For this purpose, for example, the current operation is adjusted and the electric motor is operated in such a way that the intermediate circuit is discharged to achieve the safe state. In particular, a so-called "active short-circuit state" ("AKS") is implemented to achieve the safe state. In this active short-circuit state, for example, the high-side and low-side switches of an inverter associated with the electric motor are simultaneously switched on. In other words, the phases of the electric motor are short-circuited to achieve the safe state.

[0003] Depending on the operating state from which the safe state is assumed, i.e., the operating state in which the fault condition occurs, the implementation of the active short-circuit state can generate large transient currents, which can generate strong reverse fields in the electric machine, particularly if the electrical energy storage device has been disconnected or "tripped" during the fault condition. In particular, when the operating temperature of the electric machine increases, for example, if the electric machine has previously been in continuous operation, the reverse fields at elevated operating temperatures can potentially lead to demagnetization of the permanent magnets of the electric machine, particularly those in the rotor. To prevent this, permanent magnets containing rare earth elements are used, which increase the demagnetization resistance of the permanent magnets. In other words, by using permanent magnets containing rare earth elements, particularly terbium and dysprosium, demagnetization of the permanent magnets can be reliably prevented even at elevated operating temperatures, resulting in relatively strong reverse fields.

[0004] However, efforts are underway to minimize the use of rare earth elements. This means that without the use of rare earth elements, the motor's permanent magnets could potentially demagnetize due to the generation of a reverse field at elevated operating temperatures, potentially damaging or destroying the motor, and particularly its permanent magnets. In other words, if the use of rare earth elements is reduced or eliminated, the likelihood of permanent magnet demagnetization increases when the magnet temperature rises and a reverse field is present. Summary of the Invention

[0005] The invention is based on the object of specifying a comparatively improved method for controlling the operation of an electric machine in the event of a fault, in which method, in particular, the use of rare earths can be at least reduced, without the risk of demagnetization of the permanent magnets.

[0006] This object is achieved by a method having the features of claim 1. Advantageous embodiments are the subject matter of the dependent claims.

[0007] As described, the present invention relates to a method for controlling the operation of an electric motor, in particular an electric motor of a motor vehicle, in the event of a fault. The electric motor may be part of an electric drive system of the motor vehicle, that is, the motor vehicle may be driven by the electric motor as a drive system. The electric motor is equipped with conventional components in the drive system, such as an inverter, an energy storage device, etc. The operation of the electric motor can be controlled, in particular, by the inverter outputting a corresponding voltage to set a current in the motor. As described, in the event of a fault, the electric motor should be switched to a safe state, in particular by implementing an active short-circuit state.

[0008] The invention is based on the finding that the method comprises the following steps:

[0009] - Detect the current vector of the motor;

[0010] -determining a change voltage vector based on the detected current vector;

[0011] - changing the current operating point of the motor to a changed operating point by setting a change voltage vector, wherein the power generated by the change in the operating point is equal to or less than the power loss, in particular the thermal power loss, of the motor;

[0012] - Execute active short-circuit state starting from the changed operating point.

[0013] Therefore, it is proposed to first detect the current current vector of the electric machine. In particular, the position of the current vector in a predetermined coordinate system, in particular the α-β coordinate system or the dq coordinate system, is detected. The changing voltage vector is then determined based on the detected current current vector. Here, the position of the changing voltage vector in the described coordinate system, in particular relative to the previously detected current current vector, can be determined. The changing voltage vector, for example, has a predetermined position relative to the detected current current vector.

[0014] The current operating point of the motor is then changed in a power-neutral manner to a changed operating point of the motor, at which the previously determined change voltage vector is set, wherein the power losses in the motor at least offset or exceed the power generated by the change in operating point. Therefore, in special cases, the change in the operating point can be described as "power-neutral." This means, for example, that the power generated by setting the change voltage vector from the current operating point of the motor to the changed operating point does not exceed the thermal power losses generated during this process. In other words, the change voltage vector is set while the motor is being controlled, thereby causing the operating point to change from the current operating point to the changed operating point. The change in the operating point avoids transient overcurrents, thereby preventing transient currents in the motor from generating a reverse field that could demagnetize the permanent magnets in the motor. Furthermore, the change voltage vector is selected so that the change in the operating point is performed without generating power.

[0015] Thus, by adopting the described modified operating point, the electric machine or the electrically driven device can be prepared for executing an active short-circuit state. For example, the modified operating point can be as close as possible to a "steady-state AC current" or a stable AKS current in the dq current coordinate system. With respect to this coordinate system, the transition to the modified operating point does not occur linearly, but rather follows a curved trajectory in the dq coordinate system. By changing the operating point to the modified operating point, the active short-circuit state can subsequently be executed starting from the modified operating point without large transient currents flowing in the electric machine that could generate relatively high reverse fields.

[0016] This makes it possible, even for electric machines which have no rare earths or a lower content of rare earths than in electric machines known from the prior art, to bring the electric machine into a safe state in certain fault situations by implementing an active short-circuit state.

[0017] As already described, the changing voltage vector is determined based on the detected current vector. In one embodiment of the method, the changing voltage vector can be determined to have a defined phase shift relative to the detected current vector, specifically within a range of ±π / 2. As is known, a defined phase shift between the current vector and the voltage vector (in this case, the changing voltage vector) within this range, or the described defined phase shift, does not result in power generation.

[0018] Furthermore, the prescribed phase shift can be set not exactly to ±π / 2, but rather intentionally deviated from ±π / 2. Although this generates a small amount of power, this power is offset by losses within the motor. This allows for an improved operating point change from the current operating point to the changed operating point. In particular, the small amount of power generated, offset by losses within the motor, allows for a closer approach to the desired operating point, specifically the "steady-state AC current" or the center of the spiral in the dq current coordinate system.

[0019] Purely by way of example, the prescribed phase shift between the varying voltage vector and the detected current vector may include a phase angle of 250° to 270°, particularly 255° to 265°. As already mentioned, the exact phase angle or exact phase shift can be set depending on the losses occurring in the motor. The higher the losses, the more power can be generated, as this power can be offset by the losses. In other words, the higher the losses in the motor, the further the phase shift can deviate from π / 2.

[0020] The described method can also be improved as follows: the changing voltage vector is additionally shifted relative to the detected current vector by means of at least one power-dissipating element. The prescribed phase shift can thus include this additional shift. The power-dissipating element can, for example, be an additional element within the electrical device, such as a resistor, a varistor, or the like, via which electrical power can be consumed or converted into power loss. In particular, the power-dissipating element can convert electrical energy into heat and thereby release it to the environment. For example, the power-dissipating element can be arranged in parallel with the intermediate circuit in order to dissipate the power generated by the setting of the changing voltage vector in a targeted manner in the form of power loss during the transition to the changed operating state.

[0021] In another embodiment of the method, provision can be made for setting a discharge voltage vector to reduce the voltage, in particular as a function of the detected current vector, before setting the change voltage vector. Depending on the current operating state when the fault occurs or when the fault is detected, it may be sensible to first reduce the intermediate circuit voltage in the intermediate circuit or to specifically induce a voltage drop in order to subsequently set the change voltage vector.

[0022] If the current voltage in a fault situation is higher than a specified voltage limit value, such as the permissible intermediate circuit voltage, directly setting the change voltage vector could result in an additional voltage increase. To ensure that the change voltage vector can be set without negative effects, the voltage is first reduced by setting the discharge voltage vector, so that the change voltage vector can then be set safely. The discharge voltage vector can be set in particular so that the voltage vector and the current vector are approximately synchronized, allowing for targeted active power generation and thus a voltage drop.

[0023] In the described embodiment, provision can be made, in particular, to set a discharge voltage vector as a static state vector, which delimits the vector region in which the current current vector is detected. As described, the discharge voltage vector is used to generate effective power in a targeted manner over a period of time in order to induce a voltage drop, thereby allowing a change in the voltage vector to be safely implemented or set. By using the static state vector, the switch positions in the inverter can advantageously remain static for the duration of the application of the discharge voltage vector.

[0024] In other words, the discharge voltage vector does not need to be generated by modulating or changing the switching position of the switching elements of the inverter, but the discharge voltage vector can be placed in a targeted manner in a static state vector or set in this manner. For this purpose, the current current vector can be detected, as described above. This makes it possible to identify in which vector area of the hexagon that describes the switching position of the inverter the current current vector is located in the coordinate system. Based on this, the discharge voltage vector can be set to the static state vector that defines the boundaries of the current vector area in which the current current vector is detected. In particular, the discharge voltage vector is set to a static state vector that lags behind the current vector or defines the boundaries of the vector area backward. The described setting of the discharge voltage vector as a static state vector is particularly advantageous in that neither control or regulation nor modulation of the voltage vector is required, but rather the setting of the discharge voltage vector can be performed particularly quickly and conveniently, that is, particularly with a small amount of computing time and computing power.

[0025] Furthermore, the method may provide for detecting electrical decoupling of an electrical energy storage device and / or detecting an operating event of the electrical machine and / or a motor vehicle having the electrical machine, particularly based on the operating temperature of the electrical machine, as a fault condition. As already described at the outset, the detection of a fault condition may trigger the execution of the method. Specifically, the method may be executed only if an electrical energy storage device that feeds the electrical machine or into which the electrical machine can feed energy via recuperation has electrically decoupled or a decoupling situation is pending.

[0026] In this case, it is impossible to draw energy from the energy storage device to operate the motor or change the operating state, nor is it possible to feed energy into the energy storage device during the motor's generator operation. This results in an unacceptable voltage increase when other methods are used to change the operating point before the AKS switch. Direct AKS switching (without a prior operating point change) can avoid this, but it generates large transient currents that in turn induce high reverse fields. On the other hand, if the energy storage device is not disconnected, other methods besides the one described in this application can also be used, as in this case, the power generated when changing the current operating point does not need to be taken into account.

[0027] Furthermore, operating events of the electric machine and / or the motor vehicle having the electric machine can be detected as fault conditions. Such fault conditions can, for example, describe an accident or a so-called "crash" situation. In particular, the current operating event of the electric machine, i.e., whether the electric machine is operating in motor mode or generator mode, can be included in the fault condition. As already mentioned, in generator mode, i.e., when the electrical energy storage device is decoupled, the intermediate circuit can be charged.

[0028] Even in motor operation, it may be useful to perform the method described above if, for example, voltage regulation no longer functions smoothly, for example, because the manipulated variable is no longer available to the voltage vector. As described above, a discharge voltage vector can be optionally performed in the described situation, but it is not required in all current operating states or operating events. In any case, the operating temperature of the motor can also be taken into account when detecting fault conditions. If the operating temperature is, for example, below a temperature limit, then performing the method may not be necessary, as demagnetization would not occur below this limit. Otherwise, for example, if the temperature rises above the limit, to prevent motor demagnetization, the method can be performed to change the current operating point to a changed operating point, and only then adopt or execute an active short-circuit state.

[0029] The described method can also be modified as follows: the discharge voltage vector and / or the change voltage vector can be set for a predetermined or variable time period, particularly depending on the current operating point. In a first alternative, a predetermined time period can be predefined for the discharge voltage vector and / or the change voltage vector, for which the vectors can be set. In this case, if the discharge voltage vector is set, a first time period or a discharge time period can be predefined for the discharge voltage vector. Furthermore, a second time period, which can differ from the first time period, or a change time period can be predefined for the change voltage vector.

[0030] According to a second alternative, the specified time periods, i.e., the first and / or second time periods, can be specified depending on the current operating point. This means, for example, that the first and / or second time periods can be varied depending on the current and / or voltage. Depending on the current voltage, for example, the discharge voltage vector can be set for a longer or shorter time. Similarly, depending on the current, for example, a longer time period for setting the change voltage vector can be specified at high currents, or a shorter time period for setting the change voltage vector at lower currents. As already described, the transition to the active short-circuit state occurs after the change voltage vector has been set, i.e., after adopting the changed operating point.

[0031] Furthermore, the method may provide for setting the discharge voltage vector and / or the change voltage vector to be static, or for tracking the discharge voltage vector and / or the change voltage vector, particularly based on changes in the current vector. According to the first variant described, the discharge voltage vector and / or the change voltage vector may be set to be static. This means that the discharge voltage vector and / or the change voltage vector are fixed and remain unchanged during execution. In other words, the discharge voltage vector and / or the change voltage vector are set to be static once and remain unchanged until the voltage is sufficiently reduced by the discharge voltage vector or until a changed operating state is achieved by setting the change voltage vector.

[0032] In a second alternative, provision can be made for tracking the discharge voltage vector and / or the change voltage vector. For example, changes in the current vector can be detected during the setting of the discharge voltage vector and / or the change voltage vector. As already described, the discharge voltage vector and / or the change voltage vector can be determined based on the detected current vector. By detecting changes in the current vector, different discharge voltage vectors or change voltage vectors can be determined and set at different points in time, i.e., they can be tracked together with the current vector, or the discharge voltage vector and / or the change voltage vector can be set so that they "rotate together" with the current vector.

[0033] The method can also be improved by cyclically determining the discharge voltage vector and / or the change voltage vector, particularly before a fault condition occurs. In other words, the determination can be performed cyclically during operation of the motor, so that the corresponding discharge voltage vector and / or change voltage vector is always determined for the current operating state, i.e., the currently detected current vector. Once a fault condition occurs or is detected, the last determined discharge voltage vector and / or last determined change voltage vector can be directly set without additional computational effort or time loss. This reduces the computational effort and the time associated with the determination process when a fault condition occurs or is detected. Alternatively, already determined vectors can be used and set directly.

[0034] In addition to the described method, the present invention also relates to a control device for controlling the operation of an electric motor, in particular of a motor vehicle, under a fault condition, wherein the control device is configured to detect a current current vector of the motor; determine a change voltage vector based on the detected current current vector; change the current operating point of the motor to a changed operating point by setting the change voltage vector such that the power generated by the change in operating point is equal to or less than the power loss, in particular thermal power loss, of the motor; and implement an active short-circuit state starting from the changed operating point. The control device may be, for example, an inverter of a drive device or a motor vehicle, or may include such an inverter.

[0035] The invention further relates to a drive device comprising an electric machine, an electrical energy storage device and the control device described above. The invention further relates to a motor vehicle comprising the drive device described above and / or the control device described above.

[0036] All advantages, details and features already described for the method are fully transferable to the control device, the drive device and the motor vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be explained below based on embodiments with reference to the accompanying drawings. These drawings are schematic diagrams and:

[0038] Figure 1 A schematic flow chart of a method for controlling the operation of an electric machine is shown;

[0039] Figure 2 A schematic current diagram is shown;

[0040] Figure 3 shows a schematic state diagram; and

[0041] Figure 4 A schematic voltage diagram is shown. DETAILED DESCRIPTION

[0042] Figure 1 Blocks 1-5 illustrate, by way of example, the execution of a method described herein for controlling the operation of an electric machine, in particular a drive of a motor vehicle. The electric machine may be part of a drive unit, which includes, for example, an electrical energy storage device, an inverter, and the electric machine. The inverter may be part of or form a control unit for controlling the operation of the electric machine.

[0043] The method begins, for example, in block 1, where a fault condition in the electric machine is present or detected. In block 1, it is typically possible to select whether the method described herein should be executed. For example, if no fault condition exists, the electric machine can continue normal operation. When a fault condition is detected, it can be determined, for example, whether the energy storage device of the drive unit is electrically coupled or whether a so-called battery disconnection has been performed. In this case, the energy storage device is electrically disconnected from the drive unit, so that no electrical connection exists. In this case, for example, the electric machine cannot draw energy from the energy storage device, nor can it feed energy into the energy storage device.

[0044] Optionally, other operating events of the motor vehicle, motor, or drive unit can be detected, such as whether an accident or "crash" condition has occurred. Optionally, in block 1, the operating temperature of the motor or whether the current operating temperature is above or below a temperature limit can also be detected. The method described herein is specifically executed when the operating temperature of the motor is above the temperature limit, as the likelihood of demagnetization of the motor's permanent magnets is higher in this case. If a fault condition is determined to be present or to require processing in block 1, which requires execution of the method, block 1 branches to block 2.

[0045] In one embodiment of the method, blocks 2-4 can be executed repeatedly during operation of the motor or drive, so that the steps for determining or judging described below with respect to block 2-4 are already performed, and the processing of block 2-4 is limited to setting the vector that has already been determined. Similarly, the vector can be checked only when a fault condition occurs, particularly if sufficient computing power is available.

[0046] In block 2, the current vector 6 or "current vector" of the electric machine is detected. This is done, for example, Figure 3 The state diagram in FIG. 1 shows, for example, the hexagonal diagram of the static switching states of the inverter in the form of vectors v1-v6 for bridge B6. These vectors separate vector regions I-VI from one another. In principle, any inverter or any control device can be used to operate the motor. The corresponding state diagram can be transferred to these cases and is currently used for illustrative purposes only in this specific example.

[0047] In the illustrated embodiment, the current current vector 6 is, for example, located between the static state vectors v4 and v5, i.e., in vector region IV. However, the state can be changed arbitrarily, so that the current vector 6 can also be located in any other vector region I-VI or on one of the state vectors v1-v6. As described, the current vector 6 can be periodically and automatically determined in the operating state, so that the previously determined or detected current vector 6 can be directly output in block 2.

[0048] From block 2, a branch can optionally be made to block 3, in which a discharge voltage vector 7 can be determined. If, for example, the intermediate circuit voltage 9 in the intermediate circuit (see Figure 4 ) is above a defined voltage limit value 10, block 3 can be executed. If, for example, a fault condition is detected starting from the generator operation of the electric machine or occurs during the generator operation of the electric machine, so that no current can flow into the electric energy store due to the electrical decoupling of the electric energy store, this leads to charging of the intermediate circuit, resulting in an increase in the intermediate circuit voltage 9. If the intermediate circuit voltage is above the voltage limit value 10, the voltage can be initially reduced by discharging the voltage vector 7 in order to subsequently improve or enable further execution of the method. Figure 4 The voltage limit value in is approximately 850 V, which is purely an example. After the previously specified time period 11 has expired, a transition occurs into the time range 14.

[0049] Figure 3 The discharge voltage vector 7 is shown. For example, for the first time period 11 (see Figure 4) or the discharge time period can set the discharge voltage vector 7. If the discharge voltage vector 7 is not to be set, a branch can be made directly from block 2 to block 4. The discharge voltage vector 7 is determined based on the detected current vector 6. To this end, the goal is to ensure that the discharge voltage vector 7 runs as parallel as possible to the current vector 6 so that effective power can be generated, thereby reducing the intermediate circuit voltage 9 in the intermediate circuit. Figure 3 An ideal discharge voltage vector 7' is schematically shown. Since the ideal discharge voltage vector 7' lies between the static state vectors v4 and v5, relatively complex manipulation is required to set the discharge voltage vector. To simplify manipulation, for the first time period 11 described, the discharge voltage vector 7 is advantageously set to the static state vector v4, which defines the boundaries of the vector region IV in which the current vector 6 currently resides.

[0050] Purely by way of example, current vector 6 is currently located in vector region IV of the α-β coordinate system, which is bounded by state vectors v4 and v5. Therefore, discharge voltage vector 7 can be set, for example, as a backward static state vector v4, which delimits vector region IV in which current vector 6 is currently located. Alternatively, discharge voltage vector 7 can also be set as a forward state vector v5, which delimits the current vector region IV in a forward direction. This advantageously keeps inverter control particularly simple, as no modulation is required, and the switch position can be kept constant for first time period 11. Alternatively, if, for example, sufficient computing power is available or sufficiently fast control is possible, discharge voltage vector 7' can also be set.

[0051] As described, the setting of the discharge voltage vector 7 is purely optional and can be omitted if the intermediate circuit voltage 9 in the intermediate circuit is not required. Figure 4 Purely by way of example, a fault situation is shown in which a discharge voltage vector 7 is set. For example, starting from a normal operating state, a fault situation is detected at time 8, so that the energy storage device is decoupled. In the exemplary embodiment shown, the electric machine is operated in generator mode, so that the intermediate circuit voltage 9 increases due to the decoupling of the energy storage device.

[0052] Here, the intermediate circuit voltage 9 exceeds the voltage limit value 10, for example, so that the discharge voltage vector 7 is set as described. Subsequently, once the first time period 11 has expired, a branch can be made from block 3 to block 4. If, as also previously described, the electric machine is operated in motor mode and thus does not exceed the voltage limit value 10, the setting of the discharge voltage vector 7 can be omitted. For example, the discharge voltage vector 7 can be set for the first time period 11. The first time period 11 can be predetermined statically or specified depending on the current operating point, for example, the intermediate circuit voltage. For example, the first time period 11 can be selected such that, after the first time period 11 has expired, the intermediate circuit voltage 9 has fallen back below the voltage limit 10.

[0053] In block 4, a changing voltage vector 12 is determined based on the current vector 6 detected in block 2. As described, this can be performed cyclically until a fault condition occurs. In the embodiment shown, the changing voltage vector 12 is determined to have a prescribed phase shift 13 relative to the current vector 6. For example, Figure 3 As shown, the changing voltage vector 12 is offset relative to the current vector 6 by a phase angle within the range of π / 2. Alternatively, the phase shift can also be in the opposite direction, i.e., within the range of -π / 2 relative to the current vector 6. Thus, by setting the changing voltage vector 12, no active power is generated, and the current operating point of the motor can be shifted to a changed operating point without generating power. The phase angle or phase shift 13 can differ from π / 2, for example, within the range of 250° to 270°, particularly 255° to 265°.

[0054] In this case, although a small amount of real power is generated, this is offset by the losses in the motor, so the voltage in the intermediate circuit does not increase. The greater the power losses in the motor, the further the phase shift 13 deviates from π / 2. To this end, at least one power-dissipating element, such as a resistor or varistor, can be provided, which can be used to specifically convert the power into heat. This power-dissipating element can be arranged, for example, in parallel with the intermediate circuit. Furthermore, the phase shift 13 can be determined based on the operating point, for example, the current power losses in the motor. For example, if high currents are flowing in the motor, greater losses are expected, so the phase shift 13 can be selected to be correspondingly larger.

[0055] Figure 4 The changing voltage vector 12 is shown to be set for a second time period 14 or a change time period. Figure 2As shown for two different current operating points 15, 15', the operating point change does not follow a straight line but a curved path. Spiral paths 17, 17' are shown as examples, representing direct AKS switching. The operating point change achieved by varying voltage vector 12 occurs along a curved path 18 (shown as a dashed line) from operating points 15, 15' to operating points 16, 16' and thus occurs more directly than in spiral path 17. As a result, the operating point can approach the desired operating point during second time period 14, or the current operating point 15, 15' can be brought as close as possible to the desired operating point, which represents the center point of the spiral. This means that the current operating point 15, 15' can be changed to a changed operating point 16, 16', which is as close as possible to the center point of the spiral corresponding to the stable AKS current, wherein, starting from the current operating point 15, 15', the illustrated spiral is followed and at the end of the second time period 14, the changed operating point 16, 16' drawn as an example is located on the spiral and is arranged as close as possible to the center point of the spiral.

[0056] The generated discharge voltage vector 7 and the generated change voltage vector 12 can be generated statically, so that they do not change during time periods 11 and 14. Alternatively, they can be tracked using the rotating current vector 6, i.e., they can be continuously re-determined and set at different points in time within time periods 11 and 14. If vectors 7 and 12 are set statically, this offers the advantage of significantly reducing the computational and control effort. If they are continuously tracked, the accuracy of the method can be improved.

[0057] Starting from the changed operating point 16, 16' achieved in block 4, a branch can be made to block 5, in which an active short-circuit state can be implemented in order to transfer the electric machine or the electric drive device to a safe state. Figure 4 14. Obviously, setting the change voltage vector 12 allows the operating points 15, 15' to be changed to the changed operating points 16, 16' in a power-neutral manner, so that no large transient currents flow during the transition to the active short-circuit state, and therefore no high reverse fields occur. The proposed method thus makes it possible to eliminate or at least reduce the use of corresponding rare earth elements in the electric machine without the risk of demagnetization in the event of a fault, particularly when the temperature limit is exceeded and the energy storage is decoupled.

[0058] As described, the method can be performed on a control device, particularly with the aid of an inverter. The control device (or inverter) and the electric motor can be part of a drive unit. The drive unit is typically located in a motor vehicle. Therefore, all details described with respect to the method can also be applied to the control device, the drive unit, and the motor vehicle. All advantages, details, and features shown in the various embodiments can be combined, interchanged, and repurposed as desired.

[0059] List of reference numerals:

[0060] 1-5 boxes

[0061] 6 Current vector

[0062] 7.7' Discharge voltage vector

[0063] 8 Time Point

[0064] 9 Intermediate circuit voltage

[0065] 10 Voltage limit value

[0066] 11 First time period

[0067] 12 Changing voltage vector

[0068] 13 Phase Shift

[0069] 14 Second time period

[0070] 15, 15' current operating point

[0071] 16, 16' operating point after change

[0072] 17 Spiral Track

[0073] 18 Curved trajectory.

Claims

1. A method for controlling the operation of an electric machine, in particular of a motor vehicle, in the event of a fault, comprising the following steps: - detecting the current vector of the motor (6); - determining a change voltage vector (12) based on the detected current vector (6); - changing the current operating point (15, 15') of the motor to a changed operating point (16, 16') by setting the changed voltage vector (12), wherein the power generated by the change of the operating point (15, 15') is equal to or less than the power loss, in particular the thermal power loss, of the motor; - starting from the changed operating point (16, 16'), an active short-circuit state is implemented.

2. The method according to claim 1, characterized in that The changing voltage vector (12) is determined to have a prescribed phase shift (13) relative to the detected current vector (6), in particular within the range of ±π / 2.

3. The method according to claim 2, characterized in that The changing voltage vector (12) is additionally shifted relative to the detected current vector (6) according to at least one power loss element.

4. The method according to any one of the preceding claims, characterized in that Before setting the change voltage vector (12), a discharge voltage vector (7, 7') is set according to the detected current vector (6) to reduce the voltage.

5. The method according to claim 4, characterized in that The discharge voltage vector (7, 7') is set as a static state vector (v1-v6) which defines the boundaries of a vector region (I-VI) in which the present current vector (6) is detected.

6. The method according to any one of the preceding claims, characterized in that An electrical decoupling of the electrical energy store and / or an operating event of the electric machine and / or a motor vehicle having the electric machine is detected as a fault condition, in particular as a function of an operating temperature of the electric machine.

7. The method according to any one of the preceding claims, characterized in that For a predetermined time period (11, 14) or for a variable time period (11, 14), the discharge voltage vector (7, 7') and / or the change voltage vector (12) are set, in particular as a function of the current operating point.

8. The method according to any one of the preceding claims, characterized in that The discharge voltage vector (7, 7') and / or the change voltage vector (12) are statically set, or are tracked based on a change of the current vector (6).

9. The method according to any one of the preceding claims, characterized in that In particular, the discharge voltage vector (7, 7') and / or the change voltage vector (12) are determined cyclically before the fault condition occurs.

10. A control device for controlling the operation of an electric machine, in particular of a motor vehicle, in the event of a fault, wherein: The control device is used to: detect the current current vector (6) of the motor; and determine a change voltage vector (12) based on the detected current current vector (6); and change the current operating point (15, 15') of the motor to a changed operating point (16, 16') by setting the change voltage vector (12), so that the power generated due to the change of the operating point (15, 15') is equal to or less than the power loss of the motor, especially the thermal power loss; and execute an active short-circuit state starting from the changed operating point (16, 16'). 11 . A drive device comprising an electric motor, an electrical energy store and a control device according to claim 10 . 12 . A motor vehicle comprising a drive device according to claim 11 and / or a control device according to claim 10 .

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