Method for controlling the operation of an electric machine

Abstract

A method for controlling the operation of an electric machine (2), in particular an electric machine (2) of a motor vehicle (1), in a stationary state of a current vector (4) of the electric machine (2), in which the current vector (4) is stationary, wherein a phase current distribution present in the stationary state is changed by changing a d current.

Description

[0001] Method for controlling the operation of an electrical machine

[0002] The invention relates to a method for controlling the operation of an electrical machine, in particular an electrical machine of a motor vehicle, in a standstill state of a current indicator of the electrical machine, in which the current indicator is stationary.

[0003] Methods for controlling the operation of electrical machines, in particular electrical machines in motor vehicles, are generally known from the prior art. In these methods, a magnetic field is generated in order to produce a rotary movement between a rotor and a stator, for example in order to output torque for a motor vehicle drive. In this regard, it is known that in the case of electric synchronous motors (PSM, FSM), the magnetic field, in particular a stator field, always rotates synchronously with the magnetic field in the rotor. In a constantly current-applied standstill state, for example during start-up, the rotating field is therefore also stationary, so that the current vector describing the rotating field is stationary. In such a state, the current vector is therefore also in a standstill state.In electric asynchronous motors (ASM), the stator field rotates at a differential speed (slip) to the rotor, so that when the rotor rotates in the opposite direction to the desired direction, the rotor speed can become equal to the slip speed, resulting in a stationary current vector.

[0004] When the current vectors are stationary or at a standstill, an asymmetric load on the individual phases of the electrical machine can occur, depending on the current situation. Depending on the rotor position in which the standstill state is reached, a comparatively low current or almost no current can be transmitted via one phase, while a comparatively high current can be carried in at least one other phase. On the one hand, the asymmetric load can also lead to asymmetric heating of the electrical machine, which, if the standstill state persists for an extended period of time, could cause damage to the electrical machine. For this purpose, a shutdown device is known from the prior art that switches the electrical machine off after a defined period of time.Furthermore, with such an asymmetric load, the detection of at least one operating parameter of the electrical machine, in particular a winding temperature or stator temperature, by a temperature sensor may be incorrect. For example, if the temperature sensor is assigned to the phase that carries no or comparatively low current in the current situation, a significantly lower temperature or heating is assumed than, for example, that occurs in the comparatively highly loaded phase.

[0005] The invention is based on the object of specifying a method for operating an electrical machine which is improved in comparison thereto in order to prevent asymmetrical loading of the phases of an electrical machine.

[0006] The object is achieved by a method having the features of claim 1. Advantageous embodiments are the subject of the subclaims.

[0007] As described at the outset, the invention relates to a method for controlling the operation of an electrical machine, in particular an electrical machine of a motor vehicle, wherein a standstill state of the current vector of the electrical machine occurs, in which the current vector is stationary. The current vector describes the state of the rotating field, wherein the current vector is stationary in the described standstill state. As described, depending on the design of the electrical machine, for example as a synchronous machine (salient pole machine or reluctance machine) or asynchronous machine, this can occur in various operating states, for example a starting state, a slip state or the like. The invention is based on the finding that a phase current distribution present in the standstill state is changed by changing a d-current. By changing the d-current, for example an increase in the d-current ord-current component of the current vector in a synchronous machine, the phase current distribution is changed in the standstill state of the current vector.

[0008] For example, if a standstill condition exists in which an asymmetrical or uneven phase current distribution is set, the phase current distribution can be changed by deliberately changing the d-current. In particular, the phase current distribution can be changed so that a more even phase current distribution results in the standstill condition, thus preventing uneven loads on the electrical machine. If the electrical machine is designed as a non-salient-pole synchronous machine, changing the d-current, in particular increasing the d-current, does not lead to a change in the output torque of the electrical machine, so that this ultimately has no effect on the operating state of the electrical machine or the driving state of the motor vehicle.

[0009] If, for example, a standstill state of the current vector is detected in which an uneven phase current distribution exists, the d-current or the d-current component of the current vector in the dq coordinate system or the dq system can be specifically changed in order to achieve a desired phase current distribution. The phase current, which is conducted via the individual phases of the electrical machine, can be homogenized in such a way that no uneven loads, for example uneven temperature gradients, can develop within the electrical machine. Advantageously, it is therefore not necessary to limit the time during which the current vector is at standstill or to switch off the electrical machine, since uneven loading of the individual phases of the electrical machine can be prevented or reduced using the method described.

[0010] The method can provide for a d-current component of the current vector to be increased and the current vector to be rotated in a dq coordinate system. The "rotation" of the current vector is understood in this application as a rotation in the dq system. A "rotational movement" of the current vector, which corresponds to an actual rotation of the rotating field, would only be visible in the alpha-beta coordinate system. Deviating from this, reference is made here to the dq system, in which the current vector is rotated by a d-current component, but subsequently remains at the new position in the dq system. The rotation thus describes a change in position from an original position in the dq system to a final position in the dq system. As is known, the q-current component represents the torque-generating component when the synchronous machine is designed without a reluctance component.If, for example, a standstill state of the current vector is created during a start-up condition, the absolute value of the current vector can be increased and the current vector rotated in the dq coordinate system by increasing the d-current component of the current vector. Since the d-current component is changed, but the q-current component remains constant, the electric machine will provide the same torque despite the rotation of the current vector in the dq coordinate system, so that the driving condition ultimately does not change. In other words, although the absolute value of the current vector is increased, the torque output of the electric machine remains constant. This is because the change in the d-current component ultimately represents a loss component that has no influence on the torque output, but rotates the current vector in the dq coordinate system in such a way that the phase current distribution is changed, in particular can be made more uniform.

[0011] In a further development of the described method, it can be provided that the mechanical rotor angle is kept constant and the electrical rotor angle is changed. As described, by changing the d-current or the d-current component, the current vector is rotated in the dq coordinate system. The standstill state of the current vector can, as described, in particular be a starting state of an electric machine or, in general, a standstill state of the motor vehicle. In this case, the rotor of the electric machine can be stationary, so that the mechanical rotor angle is not changed in the standstill state. By changing the d-current, the electrical rotor angle is changed, namely rotated, so that the phase current distribution changes.The mechanical rotor angle can be kept constant so that the rotor of the electric machine does not rotate and can be maintained constant, for example in a starting state. In other words, the magnitude of the phase currents and their relationships to one another can be changed, but the torque output or the torque provided by the electric machine remains the same. The angular position of the phase currents to one another also changes, but the mechanical rotor angle or the rotor position is maintained. As described at the beginning, the electric machine can basically be designed in different ways, i.e. the machine type can vary depending on the intended application. Among other things, the electric machine can be designed as a non-salient pole machine, synchronous machine, asynchronous machine or reluctance machine.In embodiments of the electrical machine, in particular as a reluctance machine, it is necessary to change the q-current component in addition to changing the d-current component in order to keep the operating point (the torque) constant. In such an embodiment, it can thus be provided that in addition to changing the d-current component, in particular depending on a machine type of the electrical machine, the q-current component is changed. In asynchronous machines, the d-current and the q-current can be changed in the standstill state such that an uneven phase current distribution occurring in a slip state is changed, whereby the torque output can be kept constant. In this case, the slip state or standstill state of the current vector can be exited by the change made.

[0012] As previously described, the change in the d-current can be used to change the phase current distribution within the electrical machine when the current vector is at a standstill. The change made is therefore only useful if an uneven phase current distribution occurs. If a uniform phase current distribution already exists in the standstill state, a change is not necessary. According to one embodiment of the method, it can therefore be provided that the phase currents of the individual phases of the electrical machine are determined and that an equilibrium and / or imbalance of the phase currents is determined. In principle, within the scope of the present application, it is equivalent to determining an existing equilibrium or, alternatively, an existing imbalance. Accordingly, the implementation of the measures is reversed orIf the current equilibrium is present, no action is required, whereas if there is an imbalance, the phase current distribution needs to be changed. When determining the phase currents, their absolute value can be calculated in order to establish the relationship between the phase current absolute values. For example, it is therefore possible to consider the maximum and minimum phase current and, by comparing the maximum phase current and the minimum phase current, determine whether these lie in an equilibrium range or whether an imbalance exists. The equilibrium range can, for example, be defined such that if the minimum phase current absolute value and the maximum phase current absolute value lie in the equilibrium range, an even phase current distribution is assumed. The equilibrium range can be chosen arbitrarily.If, for example, the determination of the phase current values ​​shows that the maximum and minimum currents are very far apart, in the worst case, one phase current is 0 and at least one other phase current is approximately 1, a phase imbalance can be assumed. If the maximum and minimum phase currents are close together, for example, one phase carries a standardized phase current of 1 and the other two phases a standardized phase current of -0.5, further changes to the phase current distribution can be omitted or such a state can be defined as the "best case" and thus as the target state.

[0013] According to a further embodiment of the method, the phase current distribution can be changed such that a phase to which a temperature sensor is assigned carries the highest phase current. As described, a temperature sensor can be assigned to one of the phases in order to determine a temperature of the phase or of the electrical machine, which can then be passed on to further control and / or regulation processes. If an uneven phase current distribution exists, this can lead to the temperature sensor detecting an incorrect temperature of the electrical machine or phase, and in particular, the actual temperature can be underestimated.

[0014] According to the described embodiment, the phase current distribution can be changed so that the phase in which the temperature sensor detects the temperature carries the highest phase current. This results in the highest temperature input being carried out in the phase in which the temperature is measured, so that the temperature input or heat input is not underestimated. To do this, you can first determine or specify which phase the temperature sensor is assigned to. The maximum phase current can then be determined by determining the individual phase currents or their amounts. A comparison can then be made to determine whether the maximum phase current is already carried in the phase to which the temperature sensor is assigned. If this is not the case, the phase current distribution can be changed, as described, so that when the current vector is at a standstill, the highest phase current is carried in the temperature-measured phase.

[0015] The described method can further be developed such that a change in the phase current distribution is changed depending on a current magnitude, in particular exclusively above a minimum current threshold. The design takes into account that the effect caused by the uneven phase current distribution ultimately depends on the magnitude of the current or the current amount. In other words, with a comparatively low current carried in the electrical machine, the uneven phase current distribution will have a minor effect. Depending on the percentage utilization in the electrical machine when the current indicator is at standstill, the uneven phase current distribution will have a greater or lesser effect.For example, the described embodiment can provide for a smaller change in the phase current distribution for small current amounts, for example, below a minimum current threshold, or for the phase current distribution to be omitted altogether. Subsequently, a linear change in the phase current distribution can be made in an increasing current range. If the electrical machine's utilization is already in a maximum range, so that no further d-current can be applied, the change can also be omitted.

[0016] According to a further embodiment of the method, the change in the phase current distribution can be carried out iteratively. Due to the iterative change in the phase current distribution, little knowledge of the electrical machine is advantageously required. For example, the change can include or be based on a defined increment or a defined maximum value.

[0017] Ultimately, in a non-polar machine, the d-current component can be changed step by step, in particular increased in magnitude, until the phase current distribution is uniform or a desired phase current distribution is achieved. In other words, the d-current component is increased in a defined increment and the phase current distribution is then determined. If the achieved phase current distribution corresponds to the desired phase current distribution, the change in the d-current component can be stopped. If the desired phase current distribution is not achieved, the d-current component can be increased in increments until the desired phase current distribution is achieved or sufficiently close. In an asynchronous machine, the d-current component can be increased until a minimum slip is reached. This causes the rotating field to start rotating again, meaning that the standstill state is exited.Accordingly, it can be provided that the d-current is increased in order to change, in particular to increase, slip in the electrical machine.

[0018] As an alternative to the iterative change in the phase current distribution described above, the change in the phase current distribution can be made directly in a further embodiment of the method. In this case, it can be provided that the necessary change in the phase current distribution is calculated or determined, in particular based on a characteristic value, in particular a characteristic map or a characteristic curve or a predetermined table. The determination of the change in the phase current distribution can, for example, be pre-measured, for example by means of a so-called look-up table. For example, when the current vector is at a standstill, the rotor angle can be observed. In this case, it can be measured in advance to determine which change in the d-current component is necessary for which rotor angle. As an alternative to the pre-determination, a calculation or determination can also be made using simulations or models.Ultimately, the change in the d-current component that needs to be made to achieve a desired phase current distribution is determined or calculated for the specific standstill state. In addition to the method, the invention relates to a control device for controlling the operation of an electrical machine, in particular an electrical machine of a motor vehicle, in a standstill state of a current vector of the electrical machine, in which the current vector is stationary, wherein the control device is designed to change a phase current distribution present in the standstill state by changing a d-current. Furthermore, the invention relates to an electrical drive arrangement, in particular an electric axle drive, which comprises an electrical machine and a control device as described above.The invention further relates to a motor vehicle comprising a previously described control device and / or a previously described electric drive arrangement. The control device is designed to carry out the previously described method in all its details.

[0019] All advantages, details and features described with regard to the method are therefore fully transferable to the control device, the electric drive arrangement and the motor vehicle.

[0020] The invention is explained below using exemplary embodiments with reference to the figures. The figures are schematic representations and show:

[0021] Fig. 1 is a schematic diagram of a motor vehicle comprising a control device and an electric machine;

[0022] Fig. 2 shows a schematic diagram of a dq current diagram;

[0023] Fig. 3 is a schematic diagram of a flow chart according to a first embodiment;

[0024] Fig. 4 is a schematic diagram of a flow chart according to a second embodiment;

[0025] Fig. 5 is a schematic diagram of a flowchart according to a third embodiment; and Fig. 6 is a schematic diagram of a flowchart according to a fourth embodiment.

[0026] Fig. 1 shows a schematic diagram of a motor vehicle 1, which has an electric machine 2 and a control device 3 connected to the electric machine 2. The control device 3 is designed to control the operation of the electric machine 2. For example, the control device 3 can open or close loop phase currents of the electric machine 2. The electric machine 2 is specifically designed as a traction drive of the motor vehicle 1, for example as an electric axle drive. Depending on a current vector 4, which is shown by way of example in a dq current diagram or dq coordinate system in Fig. 2, a current or a defined phase current distribution for a specific operating situation can thus be supplied to the electric machine 2, such that the electric machine 2 can output a torque.

[0027] For example, the current vector 4 can be in a standstill state in which the current vector is stationary, for example when the electrical machine is starting up. As shown in Fig. 2, in the standstill state, the current vector 4, which has a q-current component, is set by way of example in order to set a defined torque. If, in the standstill state, a determination of the phase current distribution, which is explained below with reference to Figs. 3 and 4, for example, shows that the phase currents carried in the individual phases of the electrical machine 2 are uneven, the phase current distribution can be specifically changed by changing a d-current or d-current component of the current vector 4. Purely as an example, a circular line 5 represents a maximum current that can be set in the electrical machine 2.A dashed line 6 shows how the dq current, i.e. the current vector 4, can be changed without changing the torque output of the electrical machine 2. The selected example applies to a non-salient pole machine, but by changing line 6 accordingly, the example can also be transferred to any other electrical machine 2 or any other machine type. Depending on the machine type, an additional adjustment of the q current component of the current vector 4 may be necessary. Arrows 7, 8 are shown schematically, indicating the limits of the change in the current vector 4. In other words, the current vector 4 can be changed within the limits defined by the arrows 7, 8, namely by changing the d current component of the current vector 4. By changing the d current, the phase current distribution in the phases of the electrical machine 2 is changed in a defined manner.In particular, starting from an uneven phase current distribution, a desired, uniform phase current distribution within the electrical machine 2 can be achieved.

[0028] Fig. 3 shows a schematic diagram of a flow chart for determining the change in the phase current distribution. The method can start in a block 9, in which the phase currents of the electrical machine 2 are determined when the current vector 4 is at a standstill. The magnitude of the phase currents can then be determined in a block 10, and the minimum and maximum phase current magnitudes of the individual phases can be determined in a block 11. Optionally, a block 12 can determine whether the magnitude of the current vector 4 in the current operating state allows further change or whether a maximum current has already been reached and further change in the current vector 4 is therefore excluded. If the maximum current is undershot, the change can be output in block 13, so that the desired phase current distribution or an equalization of the phase current distribution previously determined in block 9-11 can be carried out.This can be achieved, as previously explained with reference to Fig. 2, by applying a d-current, or by changing the d-q current in the case of a reluctance machine. Additionally, in block 12, it can be determined whether the phase current is above a minimum current threshold. If the current falls below the minimum current threshold, a change can be suppressed or not executed.

[0029] In an asynchronous machine, by outputting the change in block 13, in particular by applying a d-current, slip in the electric machine 2 can be increased, resulting in a rotating field again and thus enabling the standstill state to be exited. This state can be maintained at least until a minimum threshold of a rotational frequency of the rotating field is reached. The change or rotation of the current vector can then be terminated. If a standstill state occurs again, it is possible to apply a d-current component again or to restart the process in block 9.

[0030] Alternatively or additionally, in particular regardless of the design of the electrical machine, as shown with reference to Fig. 4, the phase currents of the individual phases of the electrical machine 2 can be determined in a block 14, wherein the magnitude of the phase currents can be formed in a block 15. Subsequently, in a block 16, it can be determined whether the phase that is assigned a temperature sensor carries the highest phase current. If this is the case, the method for the current operating state can be ended because the temperature sensor already measures the temperature of the electrical machine 2 at the phase that carries the highest phase current, thus preventing the temperature from being underestimated.If a different phase carries the highest phase current than the phase where the temperature measurement is being performed, the program can optionally branch to block 17, which determines whether the current indicator 4 allows a further increase or change in the d-current component. If this is not the case, no change is necessary. Furthermore, block 17 can determine whether the currently carried phase current is above a minimum current threshold, as previously described.

[0031] If the phase current is above the minimum current threshold and the maximum current is not reached, the program can branch from block 17 to block 18. Alternatively, the program can branch directly from block 16 to block 18, since the determination made in block 17 is optional. In block 18, the d-current component is changed, specifically, the d-current component is increased so that the phase current distribution changes. The phase current distribution can be changed so that the phase on which the temperature measurement is performed or to which the temperature sensor is assigned carries the highest phase current after the change.

[0032] Fig. 5, 6 show two embodiments that describe the determination or implementation of the change in the d-current component. By way of example, the method in Fig. 5 starts in a block 19, in which a phase imbalance is determined, for example as previously described with reference to Fig. 3 or 4. Subsequently, in a block 20, it can be or will be determined which step size and which maximum value of the d-current component or of the d-current component and q-current component, depending on the machine type, is to be made in an iterative change. This is then applied, with a branching from block 20 to block 21 in the event of an increasing imbalance of the phase currents and from block 20 to block 22 in the event of a decreasing imbalance. Accordingly, a further increase or decrease in the d-current component is carried out in blocks 21, 22 and the d-current component is iteratively changed in block 23.In block 24, a check can then be made as to whether either a maximum current, i.e. a maximum current value of current indicator 4, or a minimum current threshold has been reached. If one of the two conditions is met, the process is terminated. If a minimum change threshold has not been reached, i.e. a desired phase current distribution has not been sufficiently achieved, so that a further change is necessary to achieve a desired equilibrium or imbalance, block 24 branches to block 20, in which a further change in the d-current component is determined depending on the increasing or decreasing imbalance and, as described, is continued iteratively until the desired phase current distribution has been achieved.

[0033] Fig. 6 shows an alternative procedure for determining the change in the phase current distribution, which deviates from the iterative procedure in Fig. 5. Analogous to the execution of the method in Fig. 5, in Fig. 6 the determination or determination of the phase imbalance, for example according to Fig. 3 or Fig. 4, begins in a block 25. Subsequently, the necessary change in the phase current distribution or the necessary change in the d-current component can be calculated or determined in a block 26. For example, the necessary change can be determined or calculated based on a look-up table, a model or a simulation. Subsequently, the change can be applied in a block 26 and the achieved phase current distribution can be determined in a block 27. In particular, it can be determined whether the desired phase current distribution has been achieved.Block 28 then determines whether the maximum current has already been reached or whether the desired phase current distribution has been sufficiently achieved. If one of the two conditions is met, the process is terminated. Alternatively, block 28 branches to block 26, where the change in the d-current component is recalculated.

[0034] The advantages, details, and features shown in the individual exemplary embodiments can be combined with one another as desired, are interchangeable, and are transferable to one another. The control device 3 is designed to carry out the method described herein. The description is therefore also fully transferable to the control device 3, the electric machine 2, and the motor vehicle 1.

[0035] Reference symbol motor vehicle electrical machine control device current pointer , 6 line , 8 arrow -28 block

Claims

Patent claims 1 . Method for controlling the operation of an electrical machine (2), in particular an electrical machine (2) of a motor vehicle (1), in a standstill state of a current vector (4) of the electrical machine (2), in which the current vector (4) is stationary, characterized in that a phase current distribution present in the standstill state is changed by changing a d-current.

2. Method according to claim 1, characterized in that a d-current component of the current vector (4) is increased and the current vector (4) is rotated in a dq-coordinate system.

3. Method according to claim 1 or 2, characterized in that the mechanical rotor angle is kept constant and the electrical rotor angle is changed, in particular a stator magnetic field is rotated in relation to the rotor angle.

4. Method according to one of the preceding claims, characterized in that in addition to the change in the d-current component, in particular depending on a machine type of the electrical machine (2), the q-current component is changed.

5. Method according to one of the preceding claims, characterized in that the phase currents of the individual phases of the electrical machine (2) are determined and a balance and / or imbalance of the phase currents is determined, in particular the imbalance between the phases is reduced.

6. Method according to one of the preceding claims, characterized in that the phase current distribution is changed such that a phase to which a temperature sensor is assigned carries the highest phase current.

7. Method according to one of the preceding claims, characterized in that a change in the phase current distribution is changed as a function of a current amount, in particular exclusively above a minimum current threshold.

8. Method according to one of the preceding claims, characterized in that the change in the phase current distribution is carried out iteratively.

9. Method according to one of the preceding claims, characterized in that the change in the phase current distribution is calculated or determined, in particular based on a characteristic value, in particular a characteristic map or a characteristic curve or a predetermined table.

10. Method according to one of the preceding claims, characterized in that the d-current is increased in order to change, in particular to increase, slip in the electrical machine (2).

11. Control device (3) for controlling the operation of an electrical machine (2), in particular an electrical machine (2) of a motor vehicle (1), in a standstill state of a current vector (4) of the electrical machine (2), in which the current vector (4) is stationary, characterized in that the control device (3) is designed to change a phase current distribution present in the standstill state by changing a d-current.

12. Electric drive arrangement, in particular electric axle drive, comprising an electric machine (2) and a control device (3) according to the preceding claim.

13. Motor vehicle (1 ), comprising a control device (3) according to claim 1 1 and / or an electric drive arrangement according to the preceding claim.

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