Method and control device for operating an electric machine, electric axle drive, motor vehicle

Abstract

A method for operating an electric machine comprises a reading step, a supply step, and an application step. The electric machine has a rotor and a stator. In the reading step, a first temperature signal (205) and a second temperature signal (215) are read. The first temperature signal (205) represents a temperature of at least a part of the stator, and the second temperature signal (215) represents a temperature of at least a part of the rotor. In the supply step, a stator signal (265) and / or a rotor signal (275) are supplied using the first temperature signal (205) and the second temperature signal (215). The stator signal (265) represents a current in the stator, and the rotor signal (275) represents a current in the rotor.In the actuation step, the stator is actuated with a current represented by the stator signal (265) and / or the rotor with a current represented by the rotor signal (275).

Description

[0001] The present invention relates to a method and a control device for operating an electric machine, to an electric axle drive and to a motor vehicle.

[0002] In electrical machines, current flows can cause temperature increases in the rotor and / or stator, which may lead to overheating of parts of the electrical machine.

[0003] Against this background, the present invention provides an improved method and an improved control device for operating an electric machine, an improved electric axle drive, and an improved motor vehicle according to the main claims. Advantageous embodiments emerge from the subclaims and the following description.

[0004] The advantages that can be achieved with the approach presented here are, in particular, that a method is created that can enable reliable operation of an electrical machine.

[0005] A method for operating an electrical machine comprises a reading step, a providing step, and a loading step. The electrical machine has a rotor and a stator. In the reading step, a first temperature signal and a second temperature signal are read in. The first temperature signal represents a temperature of at least part of the stator, and the second temperature signal represents a temperature of at least part of the rotor. In the providing step, a stator signal and, additionally or alternatively, a rotor signal are provided using the first temperature signal and the second temperature signal. The stator signal represents a current in the stator, and the rotor signal represents a current in the rotor.In the application step, the stator is subjected to a current represented by the stator signal and, additionally or alternatively, the rotor is subjected to a current represented by the rotor signal.

[0006] The electric machine can be designed as a separately excited synchronous machine, abbreviated to SESM. The stator can be designed as a non-rotatable part of the electric machine, and the rotor as a rotating part of the electric machine. For example, the stator can be arranged internally and the rotor externally. A gap can be formed between the stator and the rotor, which gap can be filled with a fluid, for example, a coolant.

[0007] When the electrical machine is in a ready-to-use state or during operation, the temperature of the stator and / or rotor may rise, for example, due to a current flowing through the stator and / or rotor. High temperatures can, for example, lead to thermal damage and can negatively impact the performance of the electrical machine and / or its components. Voltage load derating, for example, can be used to prevent thermal damage in the electrical machine. The performance data of the electrical machine can be adjusted if the temperature of a component reaches a maximum value.

[0008] The approach presented here can limit the permissible temperature of the stator and / or the rotor and shift the resulting losses to one of the components, which can advantageously influence the performance of the electrical machine. For example, a loss shift from the stator to the rotor can occur when the stator has reached a maximum temperature and the rotor has a temperature that is below the maximum permissible temperature. This can be achieved, for example, by reducing a current flow in the rotor and correspondingly increasing it in the stator, or by reducing a current flow in the stator and correspondingly increasing it in the rotor. Both variants make it possible to reduce heating in the rotor or stator by reducing the current flowing through these elements, and increasing the current flow through the other element causes a corresponding temperature increase.If, for example, a maximum design-related temperature has not yet been reached in the stator, but has been reached in the rotor, the thermal load can be shifted from the rotor to the stator, or vice versa. At the same time, by adjusting the currents, a constant electrical power output by the electrical machine can be achieved. The approach presented here can therefore also be understood as a concept for increasing the continuous power output of the electrical machine when the reduction in currents in one of the elements of the electrical machine, required due to the risk of overheating, would otherwise cause a reduction in the electrical power output by the electrical machine.

[0009] A combination of a thermal model and a current calculation for loss distribution can be enabled. In addition, a loss shift between the stator and rotor of the electric machine can be achieved, thereby increasing the achievable continuous power. In other words, the loss distribution of the electric machine can be controlled by the current distribution. This effect can be used to increase the continuous power. This can be achieved by deliberately shifting the losses by limiting the permissible power per component.

[0010] In the providing step, the stator signal and, additionally or alternatively, the rotor signal can be provided in such a way that a maximum stator temperature and / or a maximum rotor temperature is exceeded. The stator and / or the rotor should not exceed a maximum temperature to avoid damage to components of the electrical machine as much as possible.

[0011] In the provision step, the stator signal and the rotor signal can be provided in such a way that the electric machine can deliver maximum power. For this purpose, for example, the current flow through the stator can be reduced while the current flow through the rotor can be increased. In this way, electromagnetic effects of the stator when the current flow is reduced can be balanced by electromagnetic effects when the rotor is subjected to an increased current flow, or vice versa. Overall, this allows the total power output of the electric machine to be adjusted by modifying the current flows through the various components of this electric machine.

[0012] According to a further embodiment, the stator signal and the rotor signal can also be provided in the providing step in such a way that the current in the stator is reduced and the current in the rotor is increased, or that the current in the rotor is reduced and the current in the stator is increased. Such an embodiment offers the advantage of being able to adjust the thermal load in the individual components by varying the currents through the rotor or stator, respectively, without, for example, causing a reduction in the power output by the electric machine.

[0013] In the reading step, a third temperature signal can be read in, which represents a temperature of a fluid flowing through the electric machine. In the providing step, the stator signal and additionally or alternatively the rotor signal can be provided using the third temperature signal. The fluid can, for example, be a coolant, which can be arranged between the rotor and the stator and can also heat up during operation of the electric machine. Such an embodiment offers the advantage of also being able to take into account effects that can be achieved by heat dissipation by means of the coolant. For example, with a high heat dissipation coefficient from a rotor located in the electric machine, a current flow through this rotor can be set higher than if no fluid is used.By taking the (current) temperature of this fluid into account, a timely and short-term optimization of the power output of the electric machine can be achieved.

[0014] In the reading step, a fluid signal can be read in, which can represent a quantity and additionally or alternatively a flow rate of a fluid through the electric machine. In the providing step, the stator signal and additionally or alternatively the rotor signal can be provided using the fluid signal. Such an embodiment of the approach proposed here is advantageous because it also allows the heat absorption capacity of the total available fluid or the fluid currently flowing through the electric machine to be taken into account, so that, for example, a total heat dissipation capacity can also be considered when determining the current flows through the rotor or the stator.

[0015] The providing step can be carried out using a current operating point parameter of the electric machine. The operating point parameter can represent a physical quantity characterizing the current operation of the electric machine. Such an embodiment offers the advantage of taking into account the current thermal load on individual components of the electric machine when determining the current flows through the rotor or stator.

[0016] The provision step can be performed using dq-transformed current values. Such an embodiment offers the advantage of being able to adjust the current flow through the rotor or stator depending on the current rotational position of the rotor relative to the stator, thus enabling further optimization of the electrical power output of the electric machine with respect to the thermal load on the individual components of the electric machine.

[0017] The approach presented here further provides a control device configured to perform, control, or implement the steps of a variant of a method presented here in corresponding devices. This embodiment of the invention in the form of a control device also allows the problem underlying the invention to be solved quickly and efficiently.

[0018] A control device can be an electrical device that processes electrical signals, for example, sensor signals, and outputs control signals depending on them. The control device can have one or more suitable interfaces, which can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of an integrated circuit in which functions of the control device are implemented. The interfaces can also be separate integrated circuits or consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0019] Also advantageous is a computer program product with program code that can be stored on a machine-readable medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out the method according to one of the embodiments described above when the program is executed on a computer or device.

[0020] An electric axle drive for a motor vehicle comprises an electric machine, a transmission device, and an embodiment of a control device mentioned herein. Using the transmission device, a torque provided by the electric machine can be converted into a drive torque for driving at least one wheel of the motor vehicle. The transmission device can comprise a gearbox for reducing the speed of the electric machine and, optionally, a differential. The electric machine can comprise a rotor and a stator.

[0021] A motor vehicle has an embodiment of an electric axle drive mentioned herein and additionally or alternatively an embodiment of a control device mentioned herein.

[0022] The invention is explained in more detail by way of example with reference to the accompanying drawings. They show: Fig. 1 a schematic representation of an embodiment of a motor vehicle; Fig. 2 is a block diagram of an embodiment of a control device; Fig. 3 is a flowchart of an embodiment of a method for operating an electrical machine; and Fig. 4 a block diagram of an embodiment of a control device.

[0023] In the following description of preferred embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0024] Fig. 1 shows a schematic representation of an embodiment of a motor vehicle 100. The motor vehicle 100 is designed, for example, as an electric vehicle and has an electric axle drive 105, a control device 110 and an electric machine 115.

[0025] The motor vehicle 100 is shown with wheels 125, four wheels 125 by way of example only, an electrical energy storage device 120, for example a battery, and the electric axle drive 105. The electric axle drive 105 comprises the control device 110, the electric machine 115, and a transmission device 130.

[0026] Electrical energy for operating the electric machine 115 is provided by a power supply device, here the electrical energy storage device 120. The electrical energy storage device 120 is designed to provide direct current. A shaft driven by the electric machine 115 is coupled directly or using the transmission device 130 to at least one wheel 125 of the motor vehicle 100. Thus, the motor vehicle 100 can be propelled using the electric machine 115. According to one exemplary embodiment, the electric axle drive 105 comprises a housing in which the control device 110, the electric machine 115, and the transmission device 130 are arranged.

[0027] The electric machine 115 has a stator 140 and a rotor 135, with the stator 140 being arranged internally and the rotor 135 being arranged externally merely by way of example. However, it is also conceivable for the rotor 135 to be arranged internally and the stator 140 to be arranged externally, without this limiting the functionality of the approach described here.

[0028] Fig. 2 shows a block diagram of an embodiment of a control device 110. The control device 110 is similar or corresponds to the control device from Fig. 1.

[0029] The control device 110 has a unit 200 for determining, a unit 210 for calculating and a unit 220 for further calculating.

[0030] The determination unit 200, which can also be referred to as a thermal model, is designed to determine the maximum heat dissipation of the stator and the rotor, and alternatively of the fluid. For this purpose, a first temperature signal 205 and a second temperature signal 215 are input. The first temperature signal 205 represents a temperature of at least part of the stator and can also be referred to, for example, as TStator. The second temperature signal 215 represents a temperature of at least part of the rotor and can also be referred to, for example, as TRotor.

[0031] According to one embodiment, a third temperature signal 235 is read in, which represents a temperature of a fluid and can also be referred to as Tfluid. According to an additional embodiment, a fluid signal 225 is read in, which can also be referred to as Qfluid. The fluid signal 225 represents a quantity and / or a flow rate of a fluid through the electrical machine. The fluid can be configured as a cooling fluid, for example, to dissipate heat from a rotor or stator located inside the electrical machine. In order to obtain the best possible determination of the heat dissipation capacity, the current temperature of this fluid and / or a quantity and / or a flow rate of the fluid through the electrical machine can be used, so that a precise conclusion can be drawn about a potential risk of overheating of one or more components of this electrical machine.

[0032] In the determination unit 200, a stator heat signal 245 and / or a rotor heat signal 255 is provided using the temperature signals 205, 215, 235 and / or the fluid signal 225. The stator heat signal 245 may also be referred to as PmaxStator and represents a maximum heat dissipation in the stator. The rotor heat signal 255 may also be referred to as PmaxRotor and represents a maximum heat dissipation in the rotor. In other words, the unit 205 enables the maximum heat dissipation to be determined.

[0033] In the calculation unit 210, the (for example, maximum permissible) current in the stator and rotor is calculated using the stator heat signal 245 and / or the rotor heat signal 255. To this end, the unit 210 outputs a stator signal 265, which designates the current to be conducted through the stator, in particular the maximum stator current Is_max, and a rotor signal 275, which designates the current to be conducted through the rotor, in particular the maximum rotor current Ir_max. The stator signal 265 therefore represents the maximum permissible current through the stator, and the rotor signal 275 represents the maximum permissible current through the rotor without damaging these components of the electrical machine.This makes it possible to precisely adjust the current flow through the stator and / or rotor, allowing a "shift" of the thermal load to be achieved, whereby the power delivered by the electrical machine can be adjusted or optimized by adjusting the different current flows through the stator and / or rotor.

[0034] In the further calculation unit 220, optimized currents 285, 295, 298 are calculated using the stator signal 265 and / or the rotor signal 275, or output them directly to the stator or rotor. The currents 285, 295, 298 are output, for example, according to an efficiency optimum and / or maximum torque per current (MTPC). It is also conceivable that a dq transformation is performed in the further calculation unit, so that the currents to be set at the stator or rotor can also be adjusted with regard to the current phase position of the rotor of the electric machine.

[0035] According to one embodiment, the control device 110 has a tracking unit 230, which is configured to track a parameter 250 of the electric machine to the calculation unit 210 using a (current) operating point 240 of the electric machine. In this case, the parameter 250 can then also represent the current electrical, magnetic, and / or thermal conditions in the electric machine, so that the stator signal 265 or the rotor signal 275 are calculated in the calculation unit 210 using the parameter 250.

[0036] A further operating point 260, which represents, for example, an ambient temperature or an initial temperature of the fluid, is tracked for the unit 200 for determination, and an additional operating point 270, which represents, for example, a current machine parameter such as a speed or a phase shift between a current curve and a voltage curve in components of the electrical machine, is tracked for the unit 220 for further calculation.

[0037] In other words, the electrical machine operates under conditions that are optimal for efficiency, representing a normal case. A temperature limit is reached in the stator and / or rotor of the electrical machine, which can also be referred to as a separately excited synchronous machine (SESM).

[0038] When the temperature limit is reached, losses are shifted to the cooler component by adjusting id (d-portion of the flow), iq (q-portion of the flow) and if (portion of the flow that can be varied by the effects of the fluid) according to the equation M=32p⋅(Ldf⋅if⋅iq+(Ld−Lq)⋅id⋅iq) into the next most efficient range with loss limitation in the now hotter component. This expands the continuous power range: A loss limitation in the hotter component up to the maximum heat dissipation so that the temperature remains constant and a loss limitation in the hotter component below the maximum heat dissipation so that the temperature drops.

[0039] The temperature is then checked and the operating strategy is adjusted: After returning to power levels less than or equal to the maximum heat dissipated in the hotter component, the system switches back to efficiency-optimal operation, the normal case.

[0040] After reaching a certain temperature in the other component or falling below a certain temperature in the previous hotter component, the procedure for expanding the continuous power range is repeated.

[0041] Fig. Figure 3 shows a flowchart of an embodiment of a method 300 for operating an electric machine. The electric machine may be the electric machine mentioned in the previous figures.

[0042] The method 300 comprises a step 305 of reading, a step 310 of providing and a step 315 of applying.

[0043] In step 305 of reading, a first temperature signal and a second temperature signal are read in. The first temperature signal represents a temperature of at least a portion of the stator, and the second temperature signal represents a temperature of at least a portion of the rotor.

[0044] According to one embodiment, in step 305 of the reading process, a third temperature signal is read in, which represents a temperature of a fluid. According to another embodiment, in step 305 of the reading process, a fluid signal is read in, which represents a quantity and / or a flow rate of a fluid through the electric machine.

[0045] In step 310 of providing, a stator signal and / or a rotor signal is provided using the first temperature signal and the second temperature signal. The stator signal represents a current in the stator, and the rotor signal represents a current in the rotor.

[0046] According to one embodiment, the stator signal and / or the rotor signal is provided such that a maximum stator temperature and / or a maximum rotor temperature is exceeded.

[0047] According to a further embodiment, the stator signal and the rotor signal are provided such that the electric machine delivers maximum power. The stator and rotor thus deliver maximum power.

[0048] The step 310 of providing is carried out, for example, using a current operating point parameter of the electric machine and / or using dq-transformed current values.

[0049] According to one embodiment, in step 310 of providing, the stator signal and / or the rotor signal is additionally provided using the third temperature signal and / or the fluid signal.

[0050] In step 315 of applying, the stator is applied with a current represented by the stator signal and / or the rotor is applied with a current represented by the rotor signal.

[0051] Fig. 4 shows a block diagram of an embodiment of a control device 110. The control device 110 is similar or corresponds to the control device from one of the previous figures and is designed to carry out the method from Fig. 3 or a similar procedure.

[0052] The control device 110 has a unit 405 for reading, a unit 410 for providing and a unit 415 for applying.

[0053] The reading unit 405 is configured to read a first temperature signal 420 and a second temperature signal 430. The first temperature signal 420 represents a temperature of at least a portion of the stator 140, and the second temperature signal 430 represents a temperature of at least a portion of the rotor 135.

[0054] According to one embodiment, the reading unit 405 is configured to read a third temperature signal 440 representing a temperature of a fluid. According to an additional embodiment, the reading unit 405 is configured to read a fluid signal 450 representing a quantity and / or flow rate of a fluid through the electric machine.

[0055] The providing unit 410 is configured to provide a stator signal 460 and / or a rotor signal 470. The stator signal 460 is provided using the first temperature signal 420 and the second temperature signal 430 and represents a current in the stator 140. The rotor signal 470 is also provided using the first temperature signal 420 and the second temperature signal 430 and represents a current in the rotor 135.

[0056] According to one embodiment, the stator signal 460 and / or the rotor signal 470 is additionally provided using the third temperature signal 440 and / or the fluid signal 450.

[0057] The application unit 415 is designed to apply a current 480 represented by the stator signal 460 to the stator 140 and / or a current 490 represented by the rotor signal 470 to the rotor 135.

[0058] The exemplary embodiments described and shown in the figures are selected only as examples. Different exemplary embodiments can be combined with each other in their entirety or with regard to individual features. Furthermore, one exemplary embodiment can be supplemented by features of another exemplary embodiment.

[0059] Furthermore, method steps according to the invention can be repeated and carried out in a different order than that described.

[0060] If an embodiment comprises an “and / or” link between a first feature and a second feature, this can be read such that the embodiment according to one embodiment has both the first feature and the second feature and according to another embodiment has either only the first feature or only the second feature. Reference symbol 100 motor vehicles 105 electric axle drive 110 Control device 115 electric machine 120 electrical energy storage units 125 bikes 130 Gearbox 135 Rotor 140 Stator 200 units to determine 205 first temperature signal 210 Unit for calculation 215 second temperature signal 220 Unit for further calculation 225 Fluid signal 230 tracking unit 235 third temperature signal 240 operating point 245 Stator heat signal 250 parameters 255 Rotor heat signal 260 additional operating points 265 Stator signal 270 additional operating point 275 Rotor signal 285 optimized current Id 295 optimized current Iq 298 optimized current If 300 Methods for operating an electrical machine 305 Step of reading 310 Step of Deployment 315 Step of loading 405 Reading unit 410 Unit for provision 415 Unit for applying 420 first temperature signal 430 second temperature signal 440 third temperature signal 450 Fluid Signal 460 Stator signal 470 Rotor signal 480 electricity 490 electricity

Claims

[1] Method (300) for operating an electrical machine (115), wherein the electrical machine (115) has a rotor (135) and a stator (140), the method (300) comprising the following steps: Reading (305) a first temperature signal (205; 420) and a second temperature signal (215; 430), wherein the first temperature signal (205; 420) represents a temperature of at least a part of the stator (140) and wherein the second temperature signal (215; 430) represents a temperature of at least a part of the rotor (135); Providing (310) a stator signal (265; 460) and / or a rotor signal (275; 470) using the first temperature signal (205; 420) and the second temperature signal (215; 430), wherein the stator signal (265; 460) represents a current in the stator (140) and / or wherein the rotor signal (275; 470) represents a current in the rotor (135); and Applying (315) to the stator (140) a current represented by the stator signal (265; 460) and / or applying to the rotor (135) a current represented by the rotor signal (275; 470). [2] Method (300) according to claim 1, wherein in the step (310) of providing, the stator signal (265; 460) and / or the rotor signal (275; 470) is provided such that a maximum stator temperature and a maximum rotor temperature are not exceeded. [3] Method (300) according to one of the preceding claims, wherein in the step of providing (310) the stator signal (265; 460) and the rotor signal (275; 470) are provided such that the electric machine (115) delivers maximum power. [4] Method according to one of the preceding claims, wherein in the step (310) of providing, the stator signal (265; 460) and the rotor signal (275; 470) are provided such that the current in the stator (140) is reduced and the current in the rotor (135) is increased or that the current in the rotor (135) is reduced and the current in the stator (140) is increased. [5] Method (300) according to one of the preceding claims, wherein in the step (305) of reading in, a third temperature signal (235; 440) is read in, which represents a temperature of a fluid flowing through the electric machine (115), wherein in the step (310) of providing, the stator signal (265; 460) and / or the rotor signal (275; 470) is determined using the third temperature signal (235; 440). [6] Method (300) according to one of the preceding claims, wherein in the step (305) of reading in, a fluid signal (225; 450) is read in, which represents a quantity and / or a flow rate of a fluid through the electric machine (115), wherein in the step (310) of providing, the stator signal (265; 460) and / or the rotor signal (275; 470) is provided using the fluid signal (225; 450). [7] Method (300) according to one of the preceding claims, wherein the step (310) of providing is carried out using a current operating point parameter (250) of the electric machine, wherein the operating point parameter (250) represents a physical quantity representing the current operation of the electric machine (115). [8] Method (300) according to one of the preceding claims, wherein the step (310) of providing is performed using dq-transformed current values. [9] Control device (110) which is designed to carry out and / or control the steps of the method (300) according to one of the preceding claims 1 to 8 in corresponding units. [10] Electric axle drive (105) for a motor vehicle (100) with at least one electric machine (115), a transmission device (130) and a control device (110) according to claim 9. [11] Motor vehicle (100) comprising an electric axle drive (105) according to claim 10 and / or a control device (110) according to claim 9.

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