Drive device for electric vehicle, electric vehicle, and method for operating drive device in electric vehicle

Abstract

Drive device (1) for an electric vehicle (100), comprising:-an electric machine (2) having a stator (3) and a rotor (4); -a temperature determination device (12) configured to determine temperature information (13) representative of a temperature (theta) of the rotor (4) and having at least a first information state representative of a first temperature and a second information state representative of a second temperature higher than the first temperature; and-a power converter device (14) configured to provide a multi-phase current (i) to said stator (3) and having an input (16) for a torque command (15) representing a desired torque (T *), said multi-phase current (i) being representable by a space vector having a d component and a q component in a rotor flux orientation coordinate system; the electric machine (2) has a machine characteristic, according to which a value of a torque (T) is assigned to each operating point, which is a pair of values of a d component and a q component, the power converter device (14) is configured to receive the torque command (15) and determine a pair of setpoints (# imgabs0 #, # imgabs1 #) for the d component and the q component corresponding to one operating point assigned to the desired torque (T *), where, upon receipt of the first information state, the pair of setpoints (# imgabs2 #, # imgabs3 #) is determined according to a first operating mode, and upon receipt of the second information state, the pair of setpoints (# imgabs0 #, # imgabs2 #, # imgabs3 #) is determined according to a second operating mode. And upon receiving the second information state, determining the pair of setpoints (# imgabs4 #, # imgabs5 #) according to a second mode of operation wherein the setpoint of the d component (# imgabs6 #) has a higher value than at the desired torque (T *) in the first mode of operation, and wherein the setpoint of the d component (# imgabs6 #) has a higher value than at the desired torque (T *) in the second mode of operation. And wherein a setpoint (# imgabs7 #) of the q component has a lower value than at the desired torque (T *) in the first mode of operation, the power converter device (14) being configured to generate the multiphase current in accordance with the pair of setpoints (# imgabs8 #, # imgabs9 #).

Description

Field of the Invention

[0001] The present invention relates to a drive device for an electric vehicle. Furthermore, the present invention relates to an electric vehicle and a method for operating a drive device in an electric vehicle. Background Art

[0002] Electric motors having a rotor and a stator are widely known, where the stator is powered by a power converter device, especially as a drive device for an electric vehicle. A polyphase current can be represented by a space vector having a direct-axis component (d-component) and a quadrature-axis component (q-component) in a rotor flux-oriented coordinate system. Among them, setpoints for the d-component and the q-component can be selected by the power converter device within a certain degree of freedom in order to obtain a specific torque according to a torque command received by the power converter device. Generally, a drive device based on a maximum torque per stator current (MTPC) strategy is desired, which allows high efficiency and thus results in a high mileage of an electric vehicle equipped with the drive device. Among them, the MTPC strategy minimizes stator copper losses, which are usually the main losses in the electric motor.

[0003] For example, US5498945A discloses an induction motor control system for an electric vehicle. An inverter controlled by a motor controller generates voltages for three phases of the induction motor. A torque command is issued from a vehicle-level controller to the motor controller. The motor controller determines a desired quadrature-axis current and a direct-axis current according to the torque command. The desired current is provided with an approximate direct-axis current that is lower than the direct-axis current based on the peak torque per ampere relationship.

[0004] This drive device has a non-negligible rotor loss portion. In particular, in the case where the rotor is only passively cooled, a high rotor temperature may result in lower availability and a derating. Then, it is not possible to maintain operation of the drive device based on the MTPC strategy, and the current supplied to the stator must be reduced, such that the desired torque represented by the torque command cannot be achieved. Summary of the Invention

[0005] It is an object of the present invention to improve the operation of a drive device in an electric vehicle, especially to improve its performance and / or efficiency by having lower losses.

[0006] According to the present invention, this object is solved by a device for an electric vehicle, the device comprising: an electric machine having a stator and a rotor rotatably arranged relative to the stator; a temperature determination device configured to determine temperature information representing the temperature of the rotor, the temperature information having at least two information states, a first information state of the information states representing a first temperature and a second information state of the information states representing a second temperature higher than the first temperature; and a power converter device configured to supply a polyphase current to the stator, having an input for a torque command representing a desired torque to be provided by the rotor and operable according to a first operating mode and according to a second operating mode, the polyphase current being representable by a space vector having a d-component and a q-component in a rotor flux-oriented coordinate system; the electric machine having a machine characteristic according to which a value of the torque provided by the rotor is assigned to each of a plurality of operating points, each operating point being a pair of values of the d-component and the q-component, the power converter device being configured to receive the torque command and determine a pair of setpoints of the d-component and the q-component corresponding to an operating point of the operating points assigned to the desired torque, wherein, upon receiving the first information state, the pair of setpoints is determined according to the first operating mode and, upon receiving the second information state, the pair of setpoints is determined according to the second operating mode, wherein the setpoint of the d-component has a higher value than the setpoint of the d-component determined at the desired torque in the first operating mode, and wherein the setpoint of the q-component has a lower value than the setpoint of the q-component determined at the desired torque in the first operating mode, wherein the power converter device is further configured to generate the polyphase current according to the pair of setpoints.

[0007] The drive device for an electric vehicle according to the present invention includes an electric machine. The electric machine includes a stator and a rotor. The rotor is rotatably arranged relative to the stator.

[0008] The drive device further includes a temperature determination device. The temperature determination device is configured to determine temperature information. The temperature information represents the temperature of the rotor. The temperature information has at least two information states. A first information state of the information states represents a first temperature. A second information state of the information states represents a second temperature. The second temperature is higher than the first temperature.

[0009] The drive device further includes a power converter device. The power converter device is configured to supply a polyphase current to the stator. The polyphase current is representable by a space vector having a d-component and a q-component in a rotor flux-oriented coordinate system. The power converter device has an input for a torque command. The torque command represents a desired torque to be provided by the rotor. The power converter device is operable according to a first operating mode and according to a second operating mode.

[0010] The electric machine has a machine characteristic. According to the machine characteristic, a value of the torque provided by the rotor is assigned to each of a plurality of operating points. Each operating point is a pair of values of a d-component and a q-component. The power converter is configured to receive a torque command. The power converter is further configured to determine a pair of setpoints of the d-component and the q-component. The pair of setpoints corresponds to one of the operating points assigned to the desired torque. When receiving a first information state, the pair of setpoints is determined according to a first operating mode.

[0011] When receiving a second information state, the pair of setpoints is determined according to a second operating mode. In the second operating mode, the setpoint of the d-component has a higher value than the setpoint of the d-component determined at the desired torque in the first operating mode. In addition, in the second operating mode, the setpoint of the q-component has a lower value than the setpoint of the q-component determined at the desired torque in the first operating mode. The power converter device is further configured to generate the polyphase current according to the pair of setpoints.

[0012] The present invention is particularly based on the consideration that the rotor losses are mainly determined by the q-component of the space vector. That is, at the same torque, by reducing the q-component and increasing the d-component, lower rotor losses can be achieved. Since the machine characteristic of the electric machine has a plurality of operating points, which results in the desired torque described by the torque command, it is proposed to use a pair of setpoints that causes the desired torque, which has a lower q-component and correspondingly a higher d-component in a second operating mode covering a higher second temperature.

[0013] Therefore, when the rotor temperature is relatively high, it is possible to advantageously reduce or prevent a further increase in the rotor temperature or rotor losses without reducing the torque. Although such a control strategy may result in higher stator losses, the proposed control strategy is particularly useful in cases where the rotor usually heats up more than the stator, for example, due to design limitations caused by the difficulty of cooling the rotor compared to the stator. In other words, when the rotor temperature is a limiting factor for providing the desired torque, the present invention provides the possibility of maintaining or achieving the desired torque, where a higher amount of stator losses can be accepted if necessary.

[0014] Specifically, the electric machine may include a shaft connected to the rotor in a torque-proof manner. The electric machine may further include a machine housing. The electric machine may also include bearings that rotatably support the shaft and are particularly fixed to the machine housing. An air gap may be formed between the rotor and the stator. Preferably, the electric machine includes a cooling device configured to actively cool the stator, for example, by means of a cooling fluid. The rotor may be passively cooled via a thermal path through the shaft and bearings to the stator housing and / or via the air gap and the stator to the stator housing. Among them, by the control strategy of the present invention, the temperature of the rotor can be reduced, although the rotor is only passively cooled. In addition, the drive device according to the present invention may include a rotor position sensor configured to determine rotor angle information representing the angular position of the rotor. The rotor position sensor may be provided inside the electric machine.

[0015] The term "d-component" refers to the direct-axis component of a space vector, and the term "q-component" refers to the quadrature-axis component of a space vector. Preferably, the polyphase current is a three-phase or six-phase current. The power converter device may include a power section for supplying a polyphase current to the electric machine. Desirably, the power section may include a DC link configured to be connected to an external DC voltage source, such as a vehicle high-voltage battery. The power section may be configured to obtain a DC voltage of at least 200V, preferably at least 400V, more preferably at least 800V. The power section may include an inverter circuit. The inverter circuit may include a plurality of semiconductor switching elements, such as insulated gate bipolar transistors (IGBTs) or insulated gate field effect transistors (IGFETs), such as silicon carbide-based metal oxide semiconductor field effect transistors (SiC-MOSFETs) or gallium nitride-based field effect transistors (GaN-FETs). Preferably, the switching elements are interconnected to a half-bridge for each phase of the polyphase current.

[0016] The power converter device may include a current measurement section configured to determine current information representing the polyphase current. Desirably, the power converter device includes a control section for determining a setpoint. The control section may obtain a torque command from an input terminal and receive temperature information. Preferably, the control section is further configured to generate switching signals for turning on and off the switching elements of the power section. The control section may include a transformation sub-section configured to transform the current information and a transformation angle into an actual d-current value and an actual q-current value. The control section may include a determination sub-section configured to determine a pair of setpoints. In particular, the determination sub-section is configured to determine the pair of setpoints based on the temperature information and the torque command.

[0017] The control part may also include a regulator sub - part, which is configured to generate the switching signal based on the pair of set - points as well as the actual d - current value and the actual q - current value. The regulator sub - part may determine the transformation angle based on rotor - angle information or sensor - less. Preferably, the regulator sub - part is configured to generate the switching signal based on field - oriented control. The regulator sub - part may also be configured to generate the switching signal based on an inverse transformation to the transformation performed by the transformation sub - part (in particular based on the transformation angle).

[0018] In addition, the drive device may include a gearbox mechanically coupled to the shaft. Exemplarily, the gearbox may connect the shaft of the electric machine to the wheel hub via one or more gears. Preferably, the electric machine, the temperature - determination device, and the power - converter device, and optionally the gearbox are arranged in an integral housing.

[0019] Regarding the drive device according to the present invention, the machine characteristics may have MTPC operating points assigned corresponding values of torque. In other words, for each value of torque, there is an operating point that satisfies the per - current maximum - torque criterion regarding the poly - phase current. At the MTPC operating point, the copper losses inside the stator are minimized. Note that the MTPC criterion does not consider rotor and iron losses. Preferably, the MTPC operating points include those operating points where the torque is maximum for the corresponding absolute values of the space vector.

[0020] Preferably, in the second operating state, the set - point of the d - component has a higher value than the d - component of the MTPC operating point assigned to the desired torque, and / or the set - point of the q - component has a lower value than the q - component of the MTPC operating point assigned to the desired torque. At the same torque, the rotor losses decrease significantly with an increase in the value of the d - component and a decrease in the value of the q - component, while the stator losses are minimum at the MTPC operating point. Thus, an operating point can be identified where the sum of the stator losses and the rotor losses is minimum at a certain torque. Such an operating point is also named the MTPL (maximum torque per loss) operating point and generally depends on the actual operating conditions of the electric machine. It has been found that for a certain torque, the MTPL operating point generally has a higher d - component than the MTPC operating point. Therefore, at least within a certain value range, the total efficiency of the electric machine can even be increased by increasing the set - point of the d - component or decreasing the set - point of the q - component respectively. Beyond the MTPL operating point, when the d - component increases, the stator losses also increase, but the rotor losses decrease.

[0021] Furthermore preferably, in the first operating mode, the pair of setpoints corresponds to the MTPC operating point assigned to the desired torque. The first operating mode is preferably selected to cover the lower temperature range of the first temperature. At these rotor temperatures, since the temperature of the rotor is not within the critical range, it may not be necessary to change from the well-established use of the MTPC operating point as a control strategy to the second operating mode with a higher d-component and a lower q-component.

[0022] Regarding the drive device according to the invention, the power converter device can also be configured to evaluate the condition according to which the temperature of the rotor reaches or exceeds a predetermined temperature threshold, which is higher than the first temperature and lower than the second temperature. Then, if the condition is not met, the power converter device can be configured to operate according to the first operating mode. Alternatively or additionally, the power converter device can be configured to operate according to the second operating mode if the condition is met. The evaluation condition allows clearly defining the temperature range covering the first temperature in which the first operating mode is applied and the temperature range covering the second temperature in which the second operating mode is applied. The threshold is generally selected with respect to the specific design of the electric machine, in particular taking into account the material parameters of the rotor. Therefore, it is proposed to select the threshold such that there is a certain margin of temperature at which the actual derating of the rotor is expected.

[0023] Ideally, in the second operating mode, when receiving an information state indicating a temperature of the rotor higher than the second temperature, the setpoint of the d-component is determined to have a higher value and the setpoint of the q-component is determined to have a lower value compared to when receiving the second information state. Alternatively or additionally, in the second operating mode, when receiving an information state indicating a temperature of the rotor lower than the second temperature and higher than the first temperature (in particular higher than the threshold), the setpoint of the d-component can be determined to have a lower value and the setpoint of the q-component can be determined to have a higher value compared to when receiving the second information state. Thus, when applying the second operating mode, the setpoint of the d-component or the setpoint of the q-component can be adapted to other temperatures in addition to the second temperature. According to a specific embodiment, the pair of setpoints can be determined by evaluating an arithmetic function depending on the desired torque and the temperature of the rotor or by using a look-up table that assigns multiple pairs of setpoints to certain intervals of the desired torque and the temperature of the rotor.

[0024] Regarding the drive device according to the invention, in the second operating mode, the pair of setpoints can be within a predetermined operating range of the machine characteristics. In other words, the determination of multiple pairs of setpoints can be restricted to a predefined operating range. In particular, the predetermined operating range excludes those pairs of setpoints where the d-component is so high that the corresponding stator loss amount does not justify a further reduction in the q-component or the rotor loss.

[0025] Preferably, the operating range is selected such that the efficiency measure for all operating points within the operating range is not lower by 10%, preferably 5%, more preferably 2% than the maximum value of the efficiency measure assigned to the same torque as the respective operating point. Thus, the reduction of the q-component in the second operating mode can be limited by considering an acceptable reduction of the motor efficiency. The corresponding efficiency measure can be the ratio of the mechanical output power of the motor to the electrical input power of the motor. For example, the operating range can be determined experimentally on a test bench with a reference machine or by simulation, in which the efficiency is determined and the corresponding boundaries of the operating range are defined.

[0026] It is also possible that the operating range is defined by a combination (in particular a linear combination) of the d-component and the q-component and / or by a predefined maximum value of the absolute value of the space vector. Limiting the operating range in this way has been considered a suitable method to exclude operating points where a further increase of the d-component cancels out the benefit of reducing the rotor losses.

[0027] In particular, the absolute value of the space vector is the square root of the sum of the squares of the d-component and the q-component.

[0028] Preferably, the temperature determination device includes a temperature sensor configured to provide a sensor signal. The temperature sensor can be arranged at the rotor, and the temperature determination device is configured to provide the sensor signal as temperature information. Thus, the temperature of the rotor can be measured directly at the rotor.

[0029] However, since it may be difficult to arrange the temperature sensor reliably at the rotating part of the motor, the temperature sensor can alternatively be arranged at the motor, preferably at the stator, where the temperature determination device can be configured to estimate the temperature of the rotor based on the sensor signal and a thermal model of the motor. Such a thermal model allows an estimation of the temperature of the rotor to be derived from one or more temperatures at other locations of the motor by considering the thermal resistance and capacitance acting between the location of the temperature sensor and the rotor. It should be noted that due to certain error tolerances in estimating the temperature of the rotor, conventional electric drives have set the stator current at a relatively low temperature limit of the rotor, such that the drive device according to the invention allows the desired torque to be provided under significantly extended operating conditions.

[0030] When the motor is an induction motor, the operating strategy described above is particularly effective. The rotor of an induction motor can only be actively cooled with very high effort, such that an improvement in performance can be achieved without the additional cost for active rotor cooling. In particular with respect to induction motors having a rotor with a rotor cage made of aluminum, the effect of the operating strategy according to the invention is very significant due to the high losses when using this material.

[0031] The above object is further solved by an electric vehicle, which includes a drive device according to the present invention, and the drive device is configured to propel the electric vehicle.

[0032] The electric vehicle may include a DC voltage source, such as a battery, for powering the power converter device. Then, the electric vehicle may be a battery electric vehicle (BEV). In addition, the electric vehicle may include an internal combustion engine, where a hybrid vehicle is formed. In addition, the electric vehicle may include a fuel cell as the DC voltage source.

[0033] Preferably, the electric vehicle may further include a control device, which is configured to provide a torque command to the input end of the drive device. The control device may be configured to evaluate the position of the accelerator pedal of the electric vehicle and provide a torque command according to this position.

[0034] The above object is further solved by a method for operating a drive device in an electric vehicle. The drive device includes: an electric machine having a stator and a rotor rotatably arranged relative to the stator; a temperature determination device; and a power converter device configured to supply a polyphase current to the stator, having an input end and operable according to a first operating mode and a second operating mode; the polyphase current can be represented by a space vector having a d-component and a q-component in a rotor flux-oriented coordinate system; the electric machine has a machine characteristic, according to which a value of the torque provided by the rotor is assigned to each of a plurality of operating points, and the operating point is a pair of values of the d-component and the q-component; the method includes the following steps: determining, by the temperature determination device, temperature information representing the rotor temperature, the temperature information having at least two information states, a first information state representing a first temperature, and a second information state representing a second temperature higher than the first temperature; receiving, at the input end of the power converter device, a torque command representing the desired torque to be provided by the rotor; determining, by the power converter device, a pair of set points of the d-component and the q-component corresponding to one of the operating points assigned to the desired torque, wherein, when receiving the first information state, this pair of set points is determined according to the first operating mode, and when receiving the second information state, this pair of set points is determined according to the second operating mode, wherein the set point of the d-component has a higher value than the set point of the d-component determined at the desired torque in the first operating mode, and wherein the set point of the q-component has a lower value than the set point of the q-component determined at the desired torque in the first operating mode; and generating, by the power converter device, a polyphase current according to this pair of set points.

[0035] All statements related to the drive device similarly apply to the electric vehicle and method according to the present invention, such that the advantages described with respect to the drive device can also be achieved by the electric vehicle and method.

[0036] In particular, the step of determining a pair of set points may include evaluating a condition according to which the temperature of the rotor reaches or exceeds a predetermined temperature threshold that is higher than a first temperature and lower than a second temperature, and operating according to a first operating mode if the condition is not met and / or operating according to a second operating mode if the condition is met.

[0037] Furthermore, the step of determining temperature information may include providing a sensor signal as the temperature information, or estimating the temperature of the rotor based on the sensor signal and a thermal model of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Further details and advantages of the present invention are disclosed hereinafter, with reference to the accompanying drawings. The drawings are schematic and show:

[0039] Figure 1 is a block diagram of an embodiment of a drive device according to the present invention;

[0040] Figure 2 is a diagram of the machine characteristics of a motor according to this embodiment;

[0041] Figure 3 is a diagram of losses and efficiency on the d - component of the space vector according to this embodiment;

[0042] Figure 4 is a block diagram of an embodiment of an electric vehicle according to the present invention; and

[0043] Figure 5 is a flowchart of an embodiment of an operating method according to the present invention. DETAILED DESCRIPTION

[0044] Figure 1 is a block diagram of an embodiment of the drive device 1.

[0045] The drive device 1 includes a motor 2 having a stator 3 and a rotor 4, the rotor 4 being rotatably arranged relative to the stator 2. The motor 2 is an induction motor having a rotor formed by an aluminum cage.

[0046] More specifically, the motor 2 further includes a shaft 5 connected to the rotor 4 in an anti - torque manner and a machine housing 6 that houses the components of the motor 2. The shaft 5 is supported by bearings 7 fixed to the machine housing 6, and an air gap 8 is formed between the rotor 4 and the stator 3. In this embodiment, the rotor 4 is passively cooled on the one hand through a thermal path via the bearings 7 and the shaft 5 to the stator housing 6 and on the other hand through a thermal path via the air gap 8 and the stator 2 to the stator housing 6. Optionally, the stator 3 is actively cooled by a cooling device 9. Furthermore, a rotor position sensor 10 of the drive device 1 is provided, and the rotor position sensor 10 is configured to determine rotor angle information 11 representing the angular position φ of the rotor 4.

[0047] The drive device 1 further includes a temperature determination device 12 configured to determine temperature information 13 representative of the temperature θ of the rotor 4. Exemplarily, the temperature determination device 12 includes a temperature sensor arranged at the stator 3 or the machine housing 6 and configured to provide a sensor signal. The signal processing member of the temperature determination device 12 may be placed outside the machine housing 6. The temperature determination device 12 is configured to estimate the temperature θ of the rotor 4 based on the sensor signal and a thermal model of the electric machine 2.

[0048] Furthermore, the drive device 1 includes a power converter device 14 configured to supply a polyphase current i to the stator 3. The polyphase current i can be represented by a space vector having a d - component and a q - component. In order to receive a torque command 15 representative of the desired torque T* to be provided by the rotor 4, the power converter device 14 includes an input terminal 16. The power converter device 14 is configured to determine a pair of setpoints for the d - component and the q - component and, based on the pair of setpoints 、 generate the polyphase current i.

[0049] More specifically, the power converter device 14 includes a power section 17 for supplying the polyphase current i to the electric machine 2, a current measurement section 18, and a control section 19.

[0050] The power section 17 includes a DC link 20 configured to be connected to an external DC voltage source 21, such as a vehicle high - voltage battery. The power section 17 is configured to obtain a DC voltage of, for example, 800 V from the DC voltage source 21. Furthermore, the power section 17 includes a DC link capacitor 22 and an inverter circuit 23 connected to the DC link capacitor 22. The inverter circuit 23 includes a plurality of semiconductor switching elements 24, exemplarily insulated gate bipolar transistors (IGBTs), which are interconnected to half - bridges 25u, 25v, 25w for each phase U, V, W of the polyphase current i.

[0051] The current measurement section 18 is configured to determine current information 26 representative of the polyphase current i. In the present embodiment, the current measurement section 18 is connected between the power section 17 and the electric machine 2. Furthermore, it is configured to provide the current information 26 such that it represents the current i of each phase U, V, W u 、i v 、i w 。

[0052] The control section 19 is configured to generate a switching signal 27 for turning on and off the switching elements 24 of the power section 17, where, for the sake of clarity, in Figure 1The connection between the control section 19 and the corresponding switching element 24 is not shown in detail. The control section 19 is configured to provide a switching signal 27 based on field-oriented control. In particular, the control section 19 includes a transformation sub-section 28, which is configured to transform the current information 26 and the transformation angle 11a into an actual d-current value i d and an actual q-current value i q . The regulator sub-section 29 of the control section 19 is configured to generate the switching signal 27 according to a pair of set points 、 、the actual d-current value i d and the actual q-current value i q . In addition, the regulator sub-section 29 is configured to generate the switching signal 27 based on a transformation opposite to the transformation performed by the transformation sub-section 28. The regulator sub-section 29 is also configured to determine the transformation angle 11a from the rotor angle information 11 and provide it to the transformation sub-section 28.

[0053] Figure 2 is a diagram of the machine characteristics of the electric machine 2 according to an embodiment. The diagram has a horizontal axis representing the normalized value i d,n of the d-component of the polyphase current i and a vertical axis representing the normalized value i q,n of the q-component of the polyphase current i.

[0054] According to the machine characteristics, a value of the torque T provided by the rotor 4 is assigned to each of a plurality of operating points. Each operating point is a pair of values of the d-component and the q-component of the space vector. In addition, Figure 2 shows a curve representing the MTPC operating points 30, and each MTPC operating point 30 is assigned a corresponding value of the torque T. The MTPC operating points 30 include those operating points where the torque is maximum for the corresponding absolute value of the space vector. In addition, in Figure 2 , a curve representing the MTPL operating points 31 is shown, where the sum 32 of the stator loss 33 and the rotor loss 34 (see Figure 3 ) is minimum for each value of the torque T. By the dashed line in Figure 2 , the contour lines of the efficiency measure are further shown, which are exemplarily selected as the ratio of the mechanical output power of the electric machine 2 to the electrical input power of the electric machine 2.

[0055] The power converter device 14 is configured to determine a pair of set points 、 of the d-component and the q-component corresponding to an operating point assigned to the desired torque T* represented by the received torque command 15. Among them, in the first information state when receiving the first information of the temperature information 13 representing the first temperature θ1 of the rotor 4, the pair of set points is determined according to the first operation mode 、 In a second information state in which temperature information 13 indicating a second temperature θ2 higher than the first temperature is received, the pair of setpoints is determined according to the second operation mode 、 。The second operation mode is different from the first operation mode in that the setpoint of the d component has a higher value than the setpoint of the d component determined at the desired torque T* in the first operation mode and the setpoint of the q component has a lower value than the setpoint of the q component determined at the desired torque T* in the first operation mode 。

[0056] Regarding Figure 2 , it is assumed that the torque command 15 requests a torque of 110 Nm. When the temperature information 13 has a first information state (i.e., a relatively low temperature θ1 of the rotor 4), the power converter device 14 operates in the first operation mode and determines the operating point 35a as a pair of setpoints 、 , which is the MTPC operating point 30. Based on the same torque command 15 of 110 Nm and the second information state indicating the higher second temperature θ2, the power converter device 14 operates in the second operation mode and determines the operating point 35b as a pair of setpoints 、 . It can be seen that when following the curve representing the requested torque of 110 Nm, the setpoint of the d component has a higher value at the operating point 35b than at the operating point 35a, while the setpoint has a lower value at the operating point 35b than at the operating point 35a.

[0057] Figure 3 shows a graph of the loss P Ln and the efficiency measure ƞ on the d component of the space vector according to an embodiment. Among them, the upper graph shows the stator loss 33, the rotor loss 34 and their sum 32 with respect to the normalized value i d,n of the d component, and the lower graph shows the efficiency measure 36 with respect to the normalized value i d,n of the d component. Both graphs refer to the above torque of 110 Nm at a rotational speed of 3,000 min -1 of the rotor 4. Note that these values are chosen for illustrative purposes only.

[0058] From Figure 3As can be seen, by increasing the d-component, the rotor loss 34 can be reduced due to the corresponding decrease in the q-component. However, the stator loss 33 has a minimum value at the MTPC operating point 30. Accordingly, the sum 32 of the stator loss 33 and the rotor loss 34 has a minimum value at a higher value of the d-component corresponding to the MTPL operating point 31, which also corresponds to the maximum value of the efficiency metric 36. That is, at a higher second temperature θ2 of the rotor 4, the operating point 35b is determined so as to reduce the rotor loss 34 and the resulting heat within the rotor 4. As can be seen at the operating point 35b, for the first temperature θ1, the same value of the efficiency metric 36 can be achieved as at the operating point 35a. When the stator 3 is actively cooled by the cooling device 9, the corresponding higher stator loss 33 at the second operating point 35b can be tolerated, while the rotor 4 is only passively cooled by the heat path leading to the stator housing 6.

[0059] In the following, a pair of setpoints for other temperatures than the first temperature θ1 and the second temperature θ2 are described 、 is determined.

[0060] According to this embodiment, the power converter device 14 is also configured to evaluate the condition according to which the temperature θ of the rotor 4 reaches or exceeds a predetermined temperature threshold θ thr , the predetermined temperature threshold θ thr is higher than the first temperature θ1 and lower than the second temperature θ2. The power converter device 14 is configured to operate according to a first operating mode if the condition is not met, and to operate according to a second operating mode if the condition is met. That is, for a temperature θ < θ thr , the first operating mode is selected, while for a temperature θ > θ thr , the second operating mode is selected.

[0061] In the first operating mode, the pair of setpoints corresponds to the MTPC operating point 30 assigned to the desired torque T*. That is, as long as the temperature of the rotor 4 does not reach or exceed the predetermined temperature threshold θ thr , the power converter device uses the MTPC operating point 30 assigned to the desired torque T* as a pair of setpoints 、 .

[0062] In the second operating mode, when receiving the temperature information 13 indicating a third temperature θ3 of the rotor that is lower than the second temperature θ2 and higher than the temperature threshold θ thr , compared to when receiving the second information state, the setpoint of the d-component is determined to have a lower value, and the setpoint of the q-component is determined to have a higher value. Exemplarily, the pair of setpoints 、 corresponding to Figure 2 the operating point 35c in. When receiving the information state indicating the fourth temperature θ4 higher than the second temperature θ4, in Figure 2 , compared with when receiving the second information state, the setpoint of the d component is determined to have a higher value, and the setpoint of the q component is determined to have a lower value. Exemplarily, this pair of setpoints , correspond to Figure 2 the operating point 35d in.

[0063] That is to say, in the second operating mode, within the range of temperature θ thr <θ3 < θ2 < θ4, the setpoint of the d component has a higher value for the corresponding higher temperature, and the setpoint of the q component has a lower value for the corresponding higher temperature. To determine a pair of setpoints thr for temperature θ > θ , , the power converter device 14 evaluates an arithmetic function depending on the desired torque T* and the temperature θ of the rotor 4.

[0064] In addition, regarding the second operating mode, it is stipulated that a pair of setpoints , is located within a pre-determined operating range 37 of the machine characteristics (see Figure 2 ). The operating range is selected such that the efficiency measure of all operating points within the operating range is not lower than the maximum value of the efficiency measure 36 assigned to the same torque T as the corresponding operating point by more than a specified percentage, such as 10%, 5% or 2%. Among them, the operating range 37 is bounded by a linear combination of the d component and the q component and a predefined maximum value of the absolute value of the space vector. Among them, the boundary forms an approximate L shape or an approximate circular sector, as can be seen from Figure 2 .

[0065] To determine a pair of setpoints , as described above, the control part 19 includes a determination subpart 38, and the determination subpart 38 is configured to determine a pair of setpoints , according to the temperature information 13 and the torque command 15. That is to say, the determination subpart 38 is configured to obtain the temperature information 13 from the temperature determination device 12, obtain the torque command 15 from the input end 16, and provide the determined pair of setpoints , to the regulator subpart 29.

[0066] According to this embodiment, the control part 19 including its sub-parts 28, 29, 38 is realized by a single piece of hardware such as a microcontroller or an FPGA.

[0067] Although not included in this article for simplicity Figure 1 , but the drive device 1 comprises a gearbox mechanically coupled to the shaft 5. The gearbox connects the shaft of the motor with the hub via a plurality of gears. The motor 2, the temperature determination device 12 and the power converter device 14 and the gearbox are arranged in an integrated housing.

[0068] According to a further embodiment, a temperature sensor is arranged at the rotor 4 and the temperature determination device 12 is configured to provide a sensor signal as temperature information 13 .

[0069] According to another embodiment, the switching element 24 is an insulated gate field effect transistor (IGFET), such as a silicon carbide-based metal oxide semiconductor field effect transistor (SiC-MOSFET) or a gallium nitride-based field effect transistor (GaN-FET).

[0070] According to another embodiment, instead of evaluating the method for determining the temperature θ>θ thr A pair of set points , The power converter device 14 or the determination sub-section 38 respectively uses a look-up table which assigns a plurality of pairs of set points to specific intervals of the desired torque T* and the temperature θ of the rotor 4 .

[0071] According to another embodiment, the sub-sections 28, 29, 38 of the control section 19 are implemented by multiple and / or distributed hardware physically connected to each other.

[0072] According to another specific embodiment, the rotor position sensor 10 is omitted and the transformation angle 11 a is determined by the controller subsection 29 based on internal data or in other words sensorlessly.

[0073] Figure 4 is a block diagram of an embodiment of an electric vehicle 100 .

[0074] The electric vehicle 100 comprises a drive device 1 according to one of the above-described embodiments, which is configured to propel the electric vehicle 100. The electric vehicle 100 further comprises a control device 101, which is configured to provide a torque command 15 to an input 16 of the drive device 1. Therein, the control device 101 can be configured to evaluate the position of an accelerator pedal 102 of the electric vehicle 100 and provide a torque command depending on the position. In addition, the vehicle 100 comprises a DC voltage source 21 connected to a DC link 20 of the drive device 1.

[0075] The electric vehicle 100 includes wheels 103 which are coupled directly or indirectly to the drive device 1, for example via a transmission, in order to rotate the wheels 103.

[0076] According to an embodiment, the electric vehicle 100 is a battery electric vehicle (BEV). Alternatively, the electric vehicle 100 may additionally include an internal combustion engine, in which case a hybrid vehicle is formed. Furthermore, the electric vehicle 100 may include a fuel cell as a DC voltage source 21, which powers the power conversion device 1.

[0077] Figure 5 is a flow chart of an embodiment of a method for operating the drive device 1 in an electric vehicle 100 such as the vehicle 100 described previously.

[0078] The method includes step S10: determining, by the temperature determination device 12, temperature information 13 representing the temperature of the rotor 4.

[0079] The method includes another step S20 of receiving, at the input 16 of the power converter device 14, a torque command 15 which represents the desired torque T* to be provided by the rotor 4.

[0080] The method includes an optional further step S30 of determining, by the rotor position sensor 10, rotor angle information 11 representing the angular position φ of the rotor 4.

[0081] The method includes another step S40 of determining, by the current measurement section 18, current information 26 representing the polyphase current i.

[0082] The method includes another step S50: determining, by the power converter device 14, in particular by the control section 19 or its determination sub-section 38, a pair of set points corresponding to one of the operating points assigned to the desired torque T*, respectively, for the d-component and the q-component 、 , where, upon receiving a first information state, the pair of set points is determined according to a first operating mode 、 , and upon receiving a second information state, the pair of set points is determined according to a second operating mode 、 , where the set point for the d-component has a higher value than the set point for the d-component determined at the desired torque T* in the first operating mode , and where the set point for the q-component has a lower value than the set point for the q-component determined at the desired torque in the first operating mode .

[0083] Step S50 includes sub-step S51: The power converter device 14, in particular the control section 19 or its determining sub-section 38, respectively evaluates the condition according to which the temperature of the rotor 4 reaches or exceeds a predetermined temperature threshold that is higher than the first temperature and lower than the second temperature.

[0084] If the condition is not met, the method branches to sub-step S52 of step S50, and if the condition is met, it branches to sub-step S53 of step S50. According to sub-step S52, the power converter device 14 is operated according to the first operating mode described in the embodiment regarding the drive device 1. According to sub-step S53, the power converter device 14 is operated according to the second operating mode described in the embodiment regarding the drive device 1.

[0085] The method further includes step S60 after step S50 or sub-steps S52 or S53 respectively. Step S60 includes generating a polyphase current i by the power converter device 14 according to the pair of setpoints , .

[0086] Step S60 includes sub-step S61: The control section 19 generates a switching signal 27 for turning on and off the switching elements 24 of the power section 17 according to the rotor angle information 11, current information 26, and the pair of setpoints , . Sub-step S61 includes: The regulator sub-section 29 determines the transformation angle 11a, in particular based on the rotor angle information 11 or based on internal data. In addition, sub-step S61 includes: The transformation sub-section 28 transforms the current information 26 and the transformation angle 11a into an actual d current value and an actual q current value , and the regulator sub-section 29 generates the switching signal 27 according to the pair of setpoints , , the actual d current value , the actual q current value and the transformation angle 11a.

[0087] In addition, step S60 includes sub-step S62 of generating the polyphase current i by the power section 17 or its inverter circuit 23 according to the switching signal 27 respectively.

Claims

1. A drive device (1) for an electric vehicle (100), comprising: - A motor (2) having a stator (3) and a rotor (4) rotatably arranged relative to the stator (3); - A temperature determination device (12) configured to determine temperature information (13) representing the temperature (θ) of the rotor (4), the temperature information (13) having at least two information states, a first information state in the information states representing a first temperature, and a second information state in the information states representing a second temperature higher than the first temperature; and - A power converter device (14) configured to supply a polyphase current (i) to the stator (3), the power converter device (14) having an input terminal (16) for a torque command (15) representing a desired torque (T*) to be provided by the rotor (4), and the power converter device (14) being operable according to a first operating mode and according to a second operating mode, the polyphase current (i) being representable by a space vector having a d-component and a q-component in a rotor flux-oriented coordinate system; The motor (2) has a machine characteristic according to which a value of the torque (T) provided by the rotor (4) is assigned to each of a plurality of operating points, each operating point being a pair of values of a d-component and a q-component. The power converter device (14) is configured to receive the torque command (15) and determine a pair of setpoints of the d-component and the q-component corresponding to an operating point among the operating points that is assigned to the desired torque (T*). , ), wherein, upon receiving the first information state, the pair of setpoints is determined according to the first operating mode. , ), and upon receiving the second information state, the pair of setpoints is determined according to the second operating mode. , ), wherein the setpoint of the d-component ) has a higher value than the setpoint of the d-component determined at the desired torque (T*) in the first operating mode. ), and wherein the setpoint of the q-component ) has a lower value than the setpoint of the q-component determined at the desired torque (T*) in the first operating mode. ), wherein the power converter device (14) is further configured to generate the polyphase current according to the pair of setpoints , ).

2. The drive device according to claim 1, wherein, The machine characteristic has an MTPC operating point (30) assigned to a corresponding value of the torque (T).

3. The drive device according to claim 2, wherein, In the second operating state, the setpoint of the d-component ( ) has a value higher than the d-component of the MTPC operating point (30) assigned to the desired torque (T*), and / or the setpoint of the q-component ( ) has a value lower than the q-component of the MTPC operating point (30) assigned to the desired torque (T*).

4. The drive device according to claim 2 or 3, wherein, In the first operating mode, the pair of setpoints ( , ) correspond to the MTPC operating points (30) assigned to the desired torque (T*).

5. The drive device according to any one of claims 2 to 4, wherein, The MTPC operating point (30) includes those operating points at which the torque (T) is maximum for the corresponding absolute value of the space vector.

6. The drive device according to any one of the preceding claims, wherein, The power converter device (14) is further configured to evaluate a condition according to which the temperature (θ) of the rotor (4) reaches or exceeds a predetermined temperature threshold higher than the first temperature and lower than the second temperature, and if the condition is not satisfied, operate according to the first operating mode, and / or if the condition is satisfied, operate according to the second operating mode.

7. The drive device according to any one of the preceding claims, wherein, In the second operating mode, when the information state indicating the temperature (θ) of the rotor (4) that is higher than the second temperature is received, compared with when the second information state is received, the setpoint of the d-component ( ) is determined to have a higher value, and the setpoint of the q-component ( ) is determined to have a lower value, and / or, when the information state indicating the temperature (θ) of the rotor (4) that is lower than the second temperature and higher than the first temperature is received, compared with when the second information state is received, the setpoint of the d-component ( ) is determined to have a lower value, and the setpoint of the q-component ( ) is determined to have a higher value.

8. The drive device according to any one of the preceding claims, wherein, In the second operating mode, the pair of setpoints ( , ) are within a predetermined operating range (37) of the machine characteristics.

9. The drive device according to claim 8, wherein, The operating range (37) is selected such that the efficiency measure of all operating points within the operating range is not lower than 10%, preferably 5%, more preferably 2% of the maximum value of the efficiency measure assigned to the same torque (T) as the corresponding operating point.

10. The drive device according to claim 9, wherein, The efficiency measure is the ratio of the mechanical output power of the motor to the electrical input power of the motor (2).

11. The drive device according to claims 8 to 10, wherein, The operating range (37) is bounded by a combination of the d-component and the q-component and / or by a predetermined maximum value of the absolute value of the space vector.

12. The drive device according to any one of the preceding claims, wherein, The temperature determination device (12) includes a temperature sensor configured to provide a sensor signal, - the temperature sensor is arranged at the rotor (4), and the temperature determination device (12) is configured to provide the sensor signal as temperature information (13), or - the temperature sensor is arranged at the electric machine (2), preferably at the stator (4), and the temperature determination device (12) is configured to estimate the temperature (θ) of the rotor (4) based on the sensor signal and a thermal model of the electric machine (2).

13. The drive device according to any one of the preceding claims, wherein, The electric machine (2) is an induction motor.

14. An electric vehicle (100) includes a drive device (1) according to any one of the preceding claims, the drive device (1) being configured to propel the electric vehicle (100).

15. A method for operating a drive device (1) in an electric vehicle (100), the drive device (1) comprising: An electric machine (2) having a stator (3) and a rotor (4) rotatably arranged relative to the stator (3); a temperature determination device (12); and a power converter device (14), the power converter device (14) being configured to supply a polyphase current (i) to the stator (3), the power converter device (14) having an input terminal (16) and being operable according to a first operating mode and a second operating mode; the polyphase current (i) can be represented by a space vector having a d-component and a q-component in a rotor flux-oriented coordinate system; the electric machine (2) has a machine characteristic according to which a value of a torque (T) provided by the rotor (4) is assigned to each of a plurality of operating points, each operating point being a pair of values of the d-component and the q-component; the method includes the following steps: - determining, by the temperature determination device (12), temperature information (13) representing the temperature (θ) of the rotor (4), the temperature information (13) having at least two information states, a first information state among the information states representing a first temperature, and a second information state among the information states representing a second temperature higher than the first temperature; - receiving, at the input terminal (16) of the power converter device (14), a torque command (15) representing a desired torque (T*) to be provided by the rotor (4); - A pair of setpoints of the d-component and the q-component corresponding to an operating point among the operating points assigned to the desired torque (T*) is determined by the power converter device (14), , ), wherein, when receiving the first information state, the pair of setpoints is determined according to the first operating mode , ), and when receiving the second information state, the pair of setpoints is determined according to the second operating mode , ), wherein the setpoint of the d-component ( ) has a higher value than the setpoint of the d-component ( ) determined at the desired torque (T*) in the first operating mode, and wherein the setpoint of the q-component ( ) has a lower value than the setpoint of the q-component ( ) determined at the desired torque (T*) in the first operating mode; and - The polyphase current (i) is generated by the power converter device (14) according to the pair of setpoints ( , ).

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