Method for controlling waste heat in an electric drive motor of a motor vehicle, electric drive unit for a motor vehicle and motor vehicle

Abstract

A method for controlling heat loss (Pv) in an electric drive machine (2) of a motor vehicle, wherein a current is supplied to the electric drive machine (2) by a control device (6), in which a ratio of a field-generating current (id) and a torque-generating current (iq) is specified to provide a predetermined heat loss (Pv), deviating from a ratio optimal for a respective operating point of the drive machine (2), characterized in that the predetermined heat loss (Pv) is provided by a drive machine (2) designed as a magnetless three-phase machine (3) by additionally adjusting a rotor current (iR) flowing through a rotor (5) of the three-phase machine (3) by the control device (6), wherein the field-generating and the torque-generating current (id, iq) are specified such that acoustic interference signals of the three-phase machine (3) are minimized by the ratio.and the rotor current (iR) is set such that the predetermined heat loss (Pv) is provided by a combination of the rotor current (iR) and the disturbance signal minimizing ratio.

Description

[0001] The invention relates to a method for controlling waste heat in an electric drive motor of a motor vehicle, wherein a current is supplied to the electric drive motor by a control device, in which a ratio of a field-generating current and a torque-generating current is specified to provide a predetermined amount of waste heat, deviating from a ratio optimal for a given operating point of the drive motor. The invention also relates to an electric drive unit and a motor vehicle.

[0002] It is already known from the prior art to use waste heat from an electric drive motor, which serves to propel a motor vehicle designed as an electric or hybrid vehicle, to heat the interior of the motor vehicle. This is described, for example, in DE 10 2012 019 005 A1. It is also known from the prior art to control the waste heat of the electric drive motor, for example, to deliberately increase it. WO 2015 / 193172 A1 describes a method for controlling the waste heat generated by a motor vehicle with an electric drive. In this method, a current is supplied to an electric motor of the electric drive by a drive control unit of the electric drive such that the ratio of field-generating current to torque-generating current is outside the optimal ratio for the respective operating point.Controlling heat loss solely from the field-generating and torque-generating current can result in the disadvantage of magnetically excited noise. This noise can be perceived by vehicle occupants and considered disturbing. Therefore, controlling heat loss can negatively impact the acoustics of the electric drive motor.

[0003] Furthermore, DE 10 2015 219 870 A1 discloses a method for operating an asynchronous machine comprising a stator and a rotor of a power unit, the gearbox of which is lubricated by means of a lubricant. The lubricant flows through the asynchronous machine and the gearbox, with the asynchronous machine being operated in a heating mode to heat the lubricant in the asynchronous machine.

[0004] The object of the present invention is to control waste heat from an electric drive motor for a motor vehicle while optimizing the acoustics of the electric drive motor.

[0005] This problem is solved according to the invention by a method, an electric drive unit, and a motor vehicle with the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the figures.

[0006] In a method according to the invention, heat loss in an electric drive motor of a motor vehicle is controlled. For this purpose, a control device supplies the electric drive motor with a current in which, to generate a predetermined amount of heat loss, a ratio of field-generating current to torque-generating current is specified, deviating from the optimal ratio of field-generating and torque-generating current for a given operating point of the drive motor. Furthermore, the predetermined heat loss is generated by a drive motor designed as a magnetless three-phase motor by additionally adjusting the rotor current flowing through the rotor of the three-phase motor via the control device. The field-generating and torque-generating currents are specified such that the ratio minimizes acoustic interference signals from the three-phase motor.The rotor current is set in such a way that the predetermined heat loss is provided through a combination of the rotor current and the disturbance signal minimizing ratio.

[0007] The invention further relates to an electric drive unit for a motor vehicle comprising an electric drive motor and a control device. The control device is designed to control heat loss from the drive motor by supplying the drive motor with a current in which, for the provision of a predetermined amount of heat loss, a ratio of field-generating current to torque-generating current is specified, deviating from the optimal ratio of field-generating and torque-generating current for a given operating point of the drive motor. Furthermore, the electric drive motor is designed as a magnetless three-phase motor.The control device is designed to additionally adjust a rotor current flowing through a rotor of the three-phase machine, and to specify the field-forming and torque-forming current in such a way that acoustic disturbance signals of the three-phase machine are minimized by the ratio, as well as to adjust the rotor current in such a way that the predetermined heat loss is provided by a combination of the rotor current and the disturbance-signal-minimizing ratio.

[0008] The electric drive machine is used to power a motor vehicle designed as an electric or hybrid vehicle and is designed as a magnetless three-phase motor. The three-phase motor has a stator that is stationary within the vehicle and a rotor that is rotatable relative to the stator. The control unit includes, in particular, an inverter through which current in the form of three-phase alternating current can be supplied to the three-phase motor. The inverter has a number of parallel-connected windings or half-bridges corresponding to the number of phases of the three-phase motor, with each winding having a series connection of switches, in particular semiconductor switches. A node between two switches is connected to a winding of the three-phase motor corresponding to one phase.A control unit of the control device allows the inverter's switches to be closed according to a predetermined pattern, converting direct current supplied by a high-voltage storage device of the electric drive unit into three-phase alternating current. This three-phase current is then fed to the three-phase motor, which generates a rotating magnetic field in the stator, driving the rotation of the rotor.

[0009] To control the torque generated by a three-phase machine, i.e., to set the machine's operating point, a so-called vector control can be used. For this purpose, stator-related three-phase quantities, in this case the three-phase alternating current supplied to the machine, are transformed into a rotor-related two-axis coordinate system with axes d and q. The torque is represented by a q-value, here by the torque-generating current, and the magnetic flux density is represented by a d-value, here by the field-generating current. The torque can be controlled as a function of several combinations of the torque-generating current and the field-generating current. The torque-generating current and the field-generating current are therefore degrees of freedom in torque control. The different combinations thus each produce the same torque, but with different efficiencies of the three-phase machine.Typically, the ratio, for example a current angle, between the field-generating current and the torque-generating current is selected by a controller in the control unit such that the power loss of the three-phase machine is minimized for the respective current operating point of the three-phase machine, thus maximizing its efficiency. The ratio between the field-generating current and the torque-generating current is therefore optimal. This optimal ratio is provided to a driver in the control unit, which then activates the inverter switches to generate the three-phase current that reflects this optimal ratio.

[0010] To provide the predetermined amount of heat loss, the three-phase machine is deliberately trimmed to intentionally increase the power loss. During trimming, the ratio between the field-generating current and the torque-generating current is deliberately selected or set by the control unit to increase the power loss and thus the heat loss. However, the currently selected ratio, which provides the desired or predetermined heat loss, can sometimes negatively affect the acoustics of the three-phase machine. In other words, the currently selected ratio can generate acoustic interference signals in the form of magnetically excited noise, which can be perceived, for example, as an unpleasant humming sound. To at least minimize these acoustic interference signals, the rotor current of the magnetless three-phase machine is also influenced.set, which represents an additional degree of freedom in torque control.

[0011] The values ​​of the field-generating current, the torque-generating current, and the rotor current are selected such that their combination minimizes noise and generates the predetermined heat loss and torque corresponding to the predetermined operating point. Choosing these current values ​​thus presents an optimization problem. Since the rotor current of the magnetless three-phase machine represents an additional degree of freedom for torque control, it also advantageously provides an additional degree of freedom for supplying the predetermined heat loss. By adjusting the rotor current, the heat loss can be generated, which is needed, for example, to heat a high-voltage storage system that supplies electrical energy to the three-phase machine and / or to heat the interior of the vehicle.This offers the advantage that additional heating devices in the vehicle can be dispensed with. Furthermore, the optimized ratio of field-generating to torque-generating current, designed to minimize disturbances, results in no or at least minimal disturbance noise during the provision of waste heat. This, in turn, improves the acoustics of the three-phase motor.

[0012] It can be provided that the predetermined heat loss is supplied by a magnetless three-phase machine designed as an asynchronous machine, wherein the rotor current is set to a current induced in the rotor and a current-inducing slip is specified by the control device. According to this embodiment, the magnetless three-phase machine of the electric drive unit is designed as an asynchronous machine. The rotor of the asynchronous machine can, for example, be designed as a squirrel-cage rotor. The stator windings generate a rotating magnetic field through the supplied three-phase alternating current, whereby a speed difference, also referred to as slip, exists between the rotating field speed and a rotor speed. This speed difference induces the current, i.e., a magnetically effective rotor current, which in turn contributes to torque generation.To adjust the rotor current, the control unit is designed to set the slip or the speed differential. The slip is set so that, together with the noise-minimizing ratio of field-generating to torque-generating current, it enables the dissipation of the predetermined heat loss. For example, the slip can be selected so that the induced current increases. This is because the increase in induced current also increases the power loss of the rotor and thus of the three-phase machine.

[0013] Alternatively, the predetermined heat loss is provided by a magnetless three-phase machine designed as a current-excited synchronous machine, whereby the rotor current is set to an excitation current, and the excitation current is specified by the control unit. According to this embodiment, the magnetless three-phase machine of the electric drive unit is designed as a current-excited synchronous machine. In the current-excited synchronous machine, the rotor also has a winding into which the excitation current can be fed, for example, via slip rings. In contrast to an asynchronous machine, in the synchronous machine the rotor rotates synchronously with the excitation field, whereby a flux generated by the excitation current in the rotor winding and the stator flux superimpose to form a resultant flux.The excitation current is adjusted by the control unit in such a way that, together with the interference-signal minimizing ratio of field-forming and torque-forming current, it enables the provision of the predetermined waste heat.

[0014] It proves advantageous if predetermined values ​​for torque and heat loss of the three-phase machine are assigned combinations of rotor current, field-generating current, and torque-generating current values. To generate the predetermined heat loss, the control unit selects the appropriate combination and specifies it for the three-phase machine based on a torque setpoint corresponding to the respective operating point. The assignment of torque and heat loss values ​​and their combinations can be stored, for example, in a conversion table or LUT (look-up table) and / or represented in a characteristic curve array. Each combination of current values, for example, provides a specific target torque and the maximum heat loss for that target torque.For each operating point of the three-phase machine, the optimal combination of current values ​​can be selected from the mapping between torques and current values. This combination will deliver the target torque corresponding to that operating point while simultaneously generating the desired heat loss. This mapping can be predetermined for the specific three-phase machine through test measurements and / or simulations, for example, during the development of the vehicle before delivery to the end customer, and stored in a vehicle-side memory device. This predetermined mapping can then be retrieved from the memory device by the control unit to operate the three-phase machine, for example, after delivery to the end customer.

[0015] In a further development of the invention, the three-phase machine is operated in a first operating mode in which the optimal ratio of field-generating current and torque-generating current is specified. To provide the predetermined heat loss, the three-phase machine is switched from the first operating mode to a second operating mode in which a ratio of field-generating and torque-generating current that deviates from the optimal ratio and minimizes interference signals is specified. In particular, the field-generating current, the torque-generating current, and the rotor current for the second operating mode are specified such that the torque of the three-phase machine in the first operating mode is kept constant during the transition to the second operating mode. The three-phase machine can be operated in both operating modes.In the first operating mode, the three-phase machine is operated efficiently by minimizing power losses. Therefore, the optimal ratio of field-generating current to torque-generating current is predefined. The rotor current is also adjusted to minimize power losses. Thus, an optimal combination of field-generating current, torque-generating current, and rotor current is provided for the three-phase machine. The first operating mode is therefore an efficient operating mode for the three-phase machine.

[0016] The three-phase motor can be switched from the first operating mode to the second. In this second mode, the motor operates inefficiently, maximizing power loss while simultaneously minimizing acoustic disturbances. The second operating mode is therefore an inefficient mode for the three-phase motor. The torque of the motor remains essentially unchanged during the switch between the first and second operating modes. In other words, the motor exhibits the same torque in the second mode as it did in the first mode before the switch. Therefore, vehicle occupants are not aware of the change between the different operating modes.

[0017] It can be provided that predetermined values ​​of the torque and heat loss of the three-phase machine are assigned first and second combinations of rotor current, field-generating current, and torque-generating current values. Depending on a target value for torque and heat loss corresponding to the respective operating point, the control unit selects the appropriate first combination in the first operating mode and the appropriate second combination in the second operating mode. The assignments between the combinations and the values ​​of torque and heat loss can, in turn, be defined as characteristic curve fields or conversion tables and stored in the vehicle's memory.To specify a predetermined target torque in the efficient, first operating mode, the first combination of current values ​​that minimizes power loss can be read from a first assignment. When switching the three-phase machine to the second, inefficient operating mode, the second combination of current values ​​corresponding to the target torque is then read from the second assignment, maximizing power loss and minimizing acoustic interference.

[0018] Preferably, the second operating mode is used to temperature-control at least one component of the vehicle by means of the waste heat generated in the second operating mode. The three-phase motor is therefore always switched from the first operating mode to the second operating mode when the at least one component of the vehicle needs to be temperature-controlled, for example, heated. This at least one component could be, for example, the interior or passenger compartment of the vehicle and / or the high-voltage storage unit of the electric drive unit. By temperature-controlling the at least one component using the waste heat generated by the three-phase motor, additional heating devices, such as an electric flow heater or heating mats in the high-voltage storage unit, can be avoided, thus eliminating the need for additional costs, extra installation space, and increased weight in the vehicle.

[0019] The invention further relates to a motor vehicle with at least one electric drive unit according to the invention or an embodiment thereof. The motor vehicle is in particular designed as an electric vehicle or hybrid vehicle. The drive unit can also include a high-voltage storage device which provides electrical energy for the three-phase motor. The electrical energy provided by the high-voltage storage device can be converted by the inverter of the control unit into three-phase alternating current and supplied to the three-phase motor.

[0020] The embodiments and advantages presented with reference to the method according to the invention apply accordingly to the electric drive unit according to the invention as well as to the motor vehicle according to the invention.

[0021] Further features of the invention will become apparent from the claims, the figure, and the figure description. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the figure description and / or shown in the figure alone, are not only usable in the combinations specified, but also in other combinations or on their own.

[0022] The invention will now be explained in more detail with reference to a preferred embodiment and the drawing.

[0023] The single figure shows a schematic representation of an embodiment of an electric drive unit according to the invention.

[0024] Figure 1 shows an electric drive unit 1 for a motor vehicle (not shown). The motor vehicle can be, for example, a passenger car in the form of an electric or hybrid vehicle and includes the electric drive unit 1 for propelling the motor vehicle. The drive unit 1 comprises an electric drive machine 2, which is designed as a magnetless three-phase machine 3. The three-phase machine 3 has a stator 4 with stator windings U, V, W, which is stationary in the motor vehicle. The three-phase machine 3 also has a rotor 5 that is rotatably mounted relative to the stator 4. The three-phase machine 3 can, for example, be designed as an asynchronous machine, in which the rotor 5 is, for example, a squirrel-cage rotor.The three-phase machine 3 can also be designed as a current-excited synchronous machine, in which the rotor 5 has a rotor winding into which an excitation current is fed.

[0025] The electric drive unit 1 further comprises a control device 6, which is designed to control the magnetless three-phase machine 3. The control device 6 includes an inverter 7 and a control unit 8 with a controller 9 and a driver 10. The inverter 7 is designed to convert direct current supplied by a high-voltage storage device (not shown) into three-phase alternating current for the three-phase machine 3. For this purpose, the inverter 7 has three half-bridges H1, H2, H3, each of which is electrically connected to one of the windings U, V, W of the stator 4. Each half-bridge H1, H2, H3 has a series connection of switching devices S0, S1, S2, S3, S4, S5, which can, for example, be semiconductor switches in the form of IGBTs or power MOSFETs.A node K1, K2, K3 between two switching devices S0, S1, S2, S3, S4, S5 is electrically connected to a stator winding U, V, W.

[0026] To supply the three-phase current to the three-phase machine 3, the switching devices S0 to S5 are closed by the driver 10 of the control unit 8 according to a predetermined pattern. This predetermined pattern is specified to the driver 10 by the controller 9, which is designed as a torque controller for regulating a torque M of the three-phase machine 3 and thus for setting an operating point of the three-phase machine 3. The torque M is regulated as a function of a ratio between a field-generating current id and a torque-generating current iq. This ratio can be set, for example, by a current angle between the field-generating current id and the torque-generating current iq. In a first operating mode of the three-phase machine 3, the ratio between the field-generating current id and the torque-generating current iq is set for the specified torque M.The target torque is selected such that the heat loss Pv provided by the three-phase machine 3 is minimized. The first operating mode is intended to operate the three-phase machine 3 with maximum efficiency. The driver 10 is designed to adjust the three-phase current by controlling and closing the corresponding switching devices S0 to S5, ensuring the optimal ratio between field-generating current id and torque-generating current iq.

[0027] The three-phase machine 3 can also be operated in a second operating mode in which a ratio between the field-generating current id and the torque-generating current iq deviates from the optimal ratio. In this second operating mode, the three-phase machine 3 is thus deliberately operated inefficiently, or trimmed, to increase the heat loss Pv. This heat loss Pv can be used, for example, to temperature-control at least one component of the vehicle, such as heating the vehicle's interior and / or the high-voltage battery. To prevent the trimming from generating unwanted noise and thus causing acoustic interference, the ratio between the field-generating current id and the torque-generating current iq is selected to minimize the acoustic interference.

[0028] To still be able to provide the desired power loss or heat loss Pv, a rotor current of the rotor 5 of the magnetless three-phase machine 3 is additionally set. In the case of the magnetless three-phase machine 3 designed as an asynchronous machine, a slip contributing to torque generation, i.e., a speed difference between the speed of the rotating field of the stator 4 and the speed of the rotor 5, can be set. This slip induces a current in the rotor 5, so that changing the slip also changes the induced current, i.e., the rotor current. In the case of the magnetless three-phase machine 3 designed as a current-excited synchronous machine, an excitation current fed into a rotor winding of the rotor 5, which contributes to torque generation, can be set.

[0029] For example, a first assignment 11 can be defined for the controller 9, in which different values ​​for the torque M and for the heat loss Pv of the three-phase machine 3 are assigned first combinations of values ​​of the field-generating current id, values ​​of the torque-generating current iq, and values ​​for setting the rotor current iR. Additionally, a second assignment 12 can be specified, in which different values ​​for the torque M and for the heat loss Pv of the three-phase machine 3 are assigned second combinations of values ​​of the field-generating current id, values ​​of the torque-generating current iq, and values ​​for setting the excitation current iR. In the case of the current-excited synchronous machine, the values ​​for setting the rotor current iR are values ​​for the excitation current. In the case of the asynchronous machine, the values ​​for setting the rotor current iR are values ​​for the slip.

[0030] The first assignment 11 is used when the first operating mode, i.e., the efficient operating mode, of the three-phase motor 3 is to be provided. This operating mode is provided, for example, when no temperature control of at least one component of the vehicle is necessary. Depending on the specified target torque M, the corresponding first combination of current values ​​is selected from the first assignment 11. If the second operating mode, for example, for temperature control of at least one component of the vehicle, is to be provided, the corresponding combination of current values ​​can be selected from the second assignment 12. When switching the three-phase motor 3 from the first to the second operating mode, the torque M of the three-phase motor 3 remains constant.The assignments 11 and 12 can, for example, be stored in a vehicle-side memory device (not shown here) and read out by the control unit 8. The combinations of current values ​​for the assignments 11 and 12 can, for example, be predetermined by test measurements and / or simulations. Reference symbol list 1 electric drive unit 2 electric drive motors 3 Three-phase machine 4 Stator 5 Rotor 6 Control unit 7 inverters 8 Control unit 9 controllers 10 drivers 11 first assignment 12 second assignment U, V, W stator windings H1, H2, H3 half-bridges S0, S1, S2, S3, S4, S5 switching devices K1, K2, K3 nodes M Moment id field-forming current iq torque-generating current iR rotor current PV waste heat

Claims

[1] Method for controlling a heat loss (Pv) in an electric drive machine (2) of a motor vehicle, wherein the electric drive machine (2) is provided with a current by a control device (6), in which, in order to provide a predetermined heat loss (Pv), a ratio of a field-forming current (id) and a torque-forming current (iq) is specified which deviates from an optimal ratio for a respective operating point of the drive machine (2), characterized byin that the predetermined heat loss (Pv) is provided by a drive machine (2) designed as a magnetless three-phase machine (3), in that a rotor current (iR) flowing through a rotor (5) of the three-phase machine (3) is additionally set by the control device (6), wherein the field-forming and the torque-forming current (id, iq) are predetermined in such a way that acoustic interference signals from the three-phase machine (3) are minimized by the ratio, and the rotor current (iR) is set in such a way that the predetermined heat loss (Pv) is provided by a combination of the rotor current (iR) and the interference-signal-minimizing ratio. [2] Method according to claim 1, characterized byin that the predetermined heat loss (Pv) is provided by a magnetless three-phase machine (3) designed as an asynchronous machine, wherein a current induced in the rotor (5) is set as the rotor current (iR) and a slip inducing the current is predetermined by the control device (6). [3] Method according to claim 1, characterized by that the predetermined heat loss (Pv) is provided by a magnetless three-phase machine (3) designed as a current-excited synchronous machine, wherein an excitation current is set as the rotor current (iR) and the excitation current is predetermined by the control device (6). [4] Method according to one of the preceding claims, characterized bythat predetermined values ​​of a torque (M) of the three-phase machine (3) and a heat loss (Pv) of the three-phase machine (3) are assigned combinations of values ​​of the rotor current (iR), the field-forming current (id) and the torque-forming current (iq), wherein in order to generate the predetermined heat loss (Pv) the corresponding combination is selected by the control device (6) and specified for the three-phase machine (3) as a function of a setpoint value of the torque (M) corresponding to the respective operating point. [5] Method according to one of the preceding claims, characterized bythat the three-phase machine (3) is operated in a first operating mode in which the optimum ratio of field-forming and torque-forming current (id, iq) is predetermined, and in order to provide the predetermined heat loss (Pv) is transferred from the first operating mode to a second operating mode in which the ratio of field-forming and torque-forming current (id, iq) which deviates from the optimum ratio and minimizes interference signals is predetermined. [6] Method according to claim 5, characterized by that the field-forming current (id), the torque-forming current (iq) and the rotor current (iR) for the second operating mode are predetermined in such a way that a torque (M) of the three-phase machine (3) in the first operating mode is kept constant when transferring to the second operating mode. [7] Method according to claim 6, characterized bythat predetermined values ​​of the torque (M) and the heat loss (Pv) of the three-phase machine (3) are assigned first combinations and second combinations of values ​​of the rotor current (iR), the field-forming current (id) and the torque-forming current (iq), wherein the corresponding first combination is selected by the control device (6) in the first operating mode and the corresponding second combination is selected in the second operating mode as a function of a setpoint value of the torque (M) and the heat loss (Pv) corresponding to the respective operating point. [8] Method according to one of claims 5 to 7, characterized by that the second operating mode for tempering at least one component of the motor vehicle is provided by means of the waste heat (Pv) provided in the second operating mode. [9] Electric drive unit (1) for a motor vehicle, comprising an electric drive machine (2) and a control device (6) which is designed to control a heat loss (Pv) of the drive machine (2) to provide the drive machine (Pv) with a current for providing a predetermined heat loss (Pv), in which a ratio of a field-forming current (id) and a torque-forming current (iq) is predetermined in a manner deviating from an optimal ratio for a respective operating point of the drive machine (2), characterized by , that - the electric drive machine (2) is designed as a magnetless three-phase machine (3) and - the control device (6) is designed to additionally set a rotor current (iR) flowing through a rotor (5) of the three-phase machine (3), and in doing so to specify the field-forming and the torque-forming current (id, iq) in such a way that acoustic interference signals from the three-phase machine (3) are minimal due to the ratio, and to set the rotor current (iR) in such a way that the predetermined heat loss (Pv) is provided by a combination of the rotor current (iR) and the interference signal-minimizing ratio. [10] Motor vehicle with at least one electric drive unit (1) according to claim 9.

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