Method and apparatus for operating an electric machine and vehicle

Abstract

The invention relates to a method for operating an electric machine (100) of a vehicle, designed as a separately excited DC motor, wherein the electric machine (100) has a rotor (110) and a stator (105) as well as a cooling circuit (125) passing through the electric machine (100). The method comprises a step of reading a speed signal (135), which represents a speed request for the electric machine (100), and a temperature signal (145), which represents a temperature detected at the rotor (110).Furthermore, the procedure includes a step of determining a rotor current signal (155), which represents a quantity of rotor current for the rotor (110), and a stator current signal (160), which represents a quantity of stator current for the stator (105), and a cooling signal (165), which represents a flow rate of coolant through the cooling circuit (125), using the speed signal (135) and the temperature signal (145).

Description

[0001] The present invention relates to a method for operating an electrical machine, in particular a separately excited DC motor, to a corresponding device and to a vehicle.

[0002] Electric or hybrid vehicles can be powered by a separately excited DC motor. In such motors, rotors can be cooled, for example, with oil cooling. Mechanical losses of the induction exciter with oil cooling of the rotor increase with increasing vehicle speed or with increasing engine speed.

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

[0004] The core of the invention lies in the advantageous replacement of mechanical losses with electrical losses using an intelligent strategy. This allows an optimum to be found that minimizes the overall losses of an electrical machine and improves cycle efficiency.

[0005] A method is presented for operating an electric machine for a vehicle, designed as a separately excited DC motor, wherein the electric machine has a rotor and a stator as well as a cooling circuit running through the electric machine. The method comprises a step of reading in a speed signal representing a speed requirement for the electric machine and a temperature signal representing a temperature prevailing at the rotor. The method also comprises a step of determining a rotor current signal representing a magnitude of a rotor current for the rotor, a stator current signal representing a magnitude of a stator current for the stator, and a cooling signal representing a flow rate of coolant through the cooling circuit, using the speed signal and the temperature signal.

[0006] The vehicle could, for example, be an electric car or a hybrid vehicle with a separately excited DC rotor motor. This can also be referred to as a separately excited synchronous motor (SESM). This means that the rotor and stator are each fed by their own voltage source, creating independent circuits: one for the rotor current and the other for the stator current. By operating the rotor with direct current and the stator with alternating current, magnetic fields dependent on the respective current flows can be created to drive the electric machine, advantageously eliminating the need for a costly permanent magnet. In the cooling circuit, a coolant, such as oil, can be passed through the stator along the rotor to cool the rotor.As the vehicle speed increases, i.e., as the engine speed increases, the oil cooling flow rate can also be increased to cool the engine, which could lead to mechanical losses. To minimize or completely prevent such losses, the method presented here can be advantageously used. In the input step, a speed signal representing the speed and a temperature signal representing the rotor temperature are input. It is to be expected that as the speed increases, the rotor temperature will also rise, perhaps with a slight delay, which would require increased cooling to protect the entire system.Instead, with the method presented here, the rotor current and the stator current can be adjusted according to a current speed or a current temperature, such that the speed can be reduced in order to keep the flow rate of coolant through the cooling circuit as low as possible. The stator currents are then adjusted to maintain a constant torque, which is possible because the parameters of the electrical machine, such as inductances and resistances, are known. For example, the rotor current can be reduced and the stator current can be increased by the same amount, so that the speed of the electrical machine can advantageously remain stable. At the same time, the oil flow rate can advantageously be reduced because the rotor temperature can be kept low.This advantageously reduces overall losses, as mechanical losses are replaced by electrical losses that can be controlled and throttled. For cycle-relevant points, electrical losses are expected to be smaller than the compensated mechanical losses. Furthermore, idle losses can also be significantly reduced.

[0007] According to one embodiment, the method can comprise an outputting step. In the outputting step, the rotor current signal can be output to a rotor supply device in order to adjust the rotor current to the magnitude of the rotor current determined in the determining step. In addition, the stator current signal can be output to a stator supply device in order to adjust the stator current to the magnitude of the stator current determined in the determining step. Furthermore, the cooling signal can be output to a pump device of the cooling circuit in order to adjust the flow rate to the flow rate determined in the determining step. For example, a specific voltage can be applied to the rotor by means of the rotor supply device, and a corresponding voltage can be applied to the stator by means of the stator supply device.The flow rate of the coolant can be controlled, for example, by means of a pump. For example, oil flow in the cooling circuit can be controlled via a valve or by directly controlling the speed of a pump. In this way, the variable determined in the determining step can be advantageously adjusted to increase overall cycle efficiency and minimize overall losses.

[0008] According to a further embodiment, the determining step can be performed using a determination rule. The determination rule can enable an assignment of speed values ​​and temperature values ​​to values ​​of the magnitude of the rotor current and the magnitude of the stator current. For example, predefined temperature threshold values ​​can be assigned to specific values ​​of the rotor current and the stator current using the determination rule, so that the magnitude of the rotor current and the magnitude of the stator current can advantageously be optimally adapted to the detected temperature values.

[0009] According to a further embodiment, a rotor current signal representing a decrease in the magnitude of the rotor current, a stator current signal representing an increase in the magnitude of the stator current, and a cooling signal representing a decrease in the flow rate can be determined in the determining step if a speed request is read in that is above a predefined threshold and, additionally or alternatively, a temperature is read in that is above a predefined threshold. For example, at higher speeds, the rotor current can be reduced depending on the rotor and stator temperatures. This can advantageously enable a reduction in the cooling current and reduce rotor losses.

[0010] According to a further embodiment, the method may include a step of detecting the temperature using a temperature detection device. For example, the temperature detection device may comprise a sensor arranged on the rotor for detecting the temperature and be configured to provide the detected temperature using the temperature signal. This offers the advantage that the rotor temperature can be continuously detected, and a rotational speed of the motor or a flow rate of the cooling fluid can be adjusted accordingly.

[0011] According to a further embodiment, the method may include a step of activating active cooling to additionally cool the stator. For example, the activation step may be performed after the rotor current signal and the stator current signal have been output to vary the current flows at the rotor and stator. For example, if an active cooling circuit is present, varying the current flow and additionally activating active cooling can advantageously increase the cooling performance, while simultaneously adjusting the currents. This can reduce the required current increase at the stator.

[0012] The approach presented here further provides a device designed 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 device also allows the problem underlying the invention to be solved quickly and efficiently.

[0013] A device can be an electrical device that processes electrical signals, for example, sensor signals, and outputs control signals depending on them. The 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 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.

[0014] In addition, a drive device for a vehicle is presented, comprising an electric machine designed as a separately excited DC motor with a cooling circuit, as well as a variant of the previously presented device. This combination offers the advantage of optimally implementing all of the aforementioned advantages.

[0015] The drive device is suitable, for example, for an electric axle drive. Such an electric axle drive for a vehicle comprises at least one drive device and a transmission device. Using the transmission device, a torque provided by the drive device can be converted into a drive torque for driving at least one wheel of the motor vehicle. The transmission device can have a transmission for reducing the speed of the electric motor and, optionally, a differential.

[0016] Accordingly, a vehicle may comprise a said drive device and additionally or alternatively a said electric axle drive.

[0017] 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.

[0018] The invention is explained in more detail by way of example with reference to the accompanying drawings. They show: Fig. 1 a block diagram of an electrical machine according to an embodiment; Fig. 2 shows a flowchart of a method for operating an electrical machine of a vehicle designed as a separately excited DC motor according to an embodiment; Fig. 3 is a flowchart of a method for operating an electrical machine of a vehicle designed as a separately excited DC motor according to an embodiment; Fig. 4 is a diagram illustrating a relationship between current flows and temperature values ​​according to an embodiment; and Fig. 5 a schematic representation of a vehicle according to an embodiment.

[0019] 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.

[0020] Fig. 1 shows a block diagram of an electric machine 100 according to one exemplary embodiment. The electric machine 100 is designed as a separately excited DC motor and can be used, for example, to operate an electric or hybrid vehicle. Such a so-called separately excited synchronous motor (SESM) comprises a stator 105 and a rotor 110 arranged rotatably within the stator 105. In this exemplary embodiment, the stator 105 is coupled by means of a stator supply device 115, for example, an inverter. The stator supply device 115 is designed to supply windings of the stator with a stator current, here with an alternating current. Independent of this current circuit, the rotor 110 in this exemplary embodiment is coupled by means of a rotor supply device 120, for example, a rectifier.The rotor supply device 120 is designed to supply a winding of the rotor 110 with a rotor current, in this case a direct current. The stator current and rotor current are provided in such a way that the rotor 110 is subjected to a torque.

[0021] The electric machine 100 also includes a cooling circuit 125 running through the electric machine 100 for cooling the rotor 110 with a coolant. In one exemplary embodiment, the cooling circuit 125 is configured to carry oil as the coolant, for example, using a pumping device 127. In the electric machine 100, which is implemented, for example, with induction exciters with oil cooling, mechanical losses increase with increasing speed when the rotor 110 rotates. This can reduce the efficiency of the entire system. The described approach enables adaptive cooling in the field-weakening range.

[0022] Therefore, the electric machine 100 presented here also comprises a device 130 designed to control the electric machine 100 including the cooling circuit 125 such that the efficiency is kept within an optimal range and, in particular, overheating of the electric machine 100 is avoided. For this purpose, the device 130 is designed to read in a speed signal 135 representing a speed requirement for the electric machine 100. In one exemplary embodiment, the speed signal 135 can be provided by a control unit 140 of a vehicle not shown in this figure. The device 130 is further designed to read in, in addition to the speed signal 135, a temperature signal 145 representing a temperature prevailing at the rotor.The temperature signal 145 can be provided merely by way of example by a temperature detection device 150 which is arranged on or adjacent to the rotor 110 and is designed to detect its temperature by sensor means.

[0023] Using the temperature signal 145 and the speed signal 135, the device 130 is configured to determine a rotor current signal 155, which represents a magnitude of a rotor current for the rotor 110. In one embodiment, the rotor current signal 155 can be output to the rotor supply device 120 to adjust the rotor current to the magnitude of the rotor current determined by the device 130.

[0024] Likewise, device 130 is configured to use temperature signal 145 and rotational speed signal 135 to determine a stator current signal 160, which represents a magnitude of a stator current for stator 105. Stator current signal 160 can be output to stator supply device 115, merely by way of example, to adjust the stator current to the magnitude of the stator current determined by device 130.

[0025] The device 130 is further configured to use the rotational speed signal 135 and the temperature signal 145 to determine a cooling signal 165, which represents a flow rate of cooling fluid through the cooling circuit 125. In one embodiment, the cooling signal 165 can be output to the pump device 127 of the cooling circuit 125 in order to adjust the flow rate to the flow rate determined by the device 130.

[0026] The mechanical losses in the electric machine 100 depend not only on the speed but also on the oil flow rate. Therefore, reducing the cooling rate can lead to lower mechanical losses. Reducing the oil flow rate is only possible if the losses at the rotor 110 are also reduced to keep the temperature within an acceptable range. Furthermore, with a separately excited DC rotor, it is possible to shift the losses from the rotor 110 to the stator 105, and vice versa, by adjusting the reference currents.

[0027] Accordingly, varying the current flow through the windings of rotor 110 and stator 105 enables a reduction in mechanical losses. This requires the ability to control the oil flow through electric machine 100, for example, by appropriately controlling a valve or by directly controlling the speed of the cooling circuit pump 125. At higher speeds, the rotor current should be reduced depending on the rotor and stator temperatures. This enables a reduction in rotor losses and a reduction in cooling current. The stator currents can then be adjusted to maintain a constant torque, which is possible because the parameters of electric machine 100, such as inductances and resistances, are known.

[0028] In one embodiment, the electric machine 100 also includes an active cooling system 170, which can be activated by the device 130, for example only, to additionally cool the stator 105 in particular. By varying the current flow and active cooling, the cooling performance can be increased and the currents can be adjusted at the same time.

[0029] According to one embodiment, the stator supply device 115 and the rotor supply device 120 are part of an inverter of a vehicle that is connected between a battery of the vehicle and the electric machine 100. According to one embodiment, the device 130 is integrated into a control device of such an inverter or into a control unit of the vehicle. Alternatively, the device 130 is embodied, for example, as a standalone device.

[0030] Fig. Figure 2 shows a flowchart of a method 200 for operating an electric machine of a vehicle embodied as a separately excited DC motor according to one exemplary embodiment. The method 200 presented here can be implemented, by way of example, for operating an electric machine as described in the previous figure.

[0031] The method 200 includes a step 205 of reading in a speed signal representing a speed request for the electric machine and a temperature signal representing a temperature prevailing at the rotor.

[0032] Furthermore, the method 200 includes a step 210 of determining a rotor current signal, a stator current signal, and a cooling signal using the speed signal and the temperature signal. The rotor current signal represents a magnitude of a rotor current for the rotor, the stator current signal represents a magnitude of a stator current for the stator, and the cooling signal represents a flow rate of cooling fluid through the cooling circuit.

[0033] If, in step 205 of reading, a speed request is read in that represents a desired speed of the electric machine that lies above a correspondingly predefined speed threshold and, additionally or alternatively, a temperature prevailing at the rotor is read in whose magnitude lies above a correspondingly predefined temperature speed threshold, then in one embodiment, in step 210 of determining, the rotor current signal is determined such that a current magnitude of the rotor current is reduced. In addition, for example, the stator current signal is determined such that a current magnitude of the stator current is increased. In addition, the cooling signal is determined such that a current flow rate is reduced. This reduces the overall losses of the electric machine because the mechanical losses, which are only dependent on the speed, are replaced by electrical losses that are controlled and throttled.

[0034] In one embodiment, the determining step 210 is followed by a step 215 of outputting the determined signals. In this case, the rotor current signal is output to a rotor supply device, merely by way of example, in order to adjust the rotor current to the rotor current magnitude determined in the determining step 210. Furthermore, the stator current signal is output to a stator supply device, by way of example, in order to adjust the stator current to the determined stator current magnitude, and the cooling signal, in one embodiment, is output to a pump device of the cooling circuit in order to adjust the flow rate to the flow rate determined in the determining step 210.

[0035] In other words, the method 200 presented here is adaptive cooling in the field-weakening range. Mechanical losses are replaced by electrical losses using an intelligent strategy. This allows an optimum to be found that minimizes the total losses of the electric machine and improves cycle efficiency.

[0036] Mechanical losses depend not only on the speed but also on the coolant flow rate, for example, the oil flow rate. Therefore, reducing the oil flow rate can lead to lower mechanical losses.

[0037] A reduction in the oil flow rate is only possible if the losses at the rotor are also reduced.

[0038] In a separately excited DC rotor, it is possible to shift the losses from the rotor to the stator by adjusting the reference currents. Therefore, in the method 200 described here, the rotor current is reduced at higher speeds, depending on the rotor and stator temperatures, to reduce the rotor losses and enable a reduction in the cooling current. The stator currents are then adjusted to maintain a constant torque despite the reduced rotor current.

[0039] Fig. 3 shows a flowchart of a method 200 for operating an electrical machine of a vehicle, designed as a separately excited DC motor, according to an exemplary embodiment. The method 200 shown here corresponds to or is similar to the method described in the preceding Fig. 2, with the difference that it has additional steps.

[0040] Thus, in this exemplary embodiment, step 205 of determining is preceded by a step 300 of detecting the temperature using a temperature detection device. In this step 300, a current temperature value on the rotor is detected by a sensor, for example only, and provided using the temperature signal.

[0041] Subsequently, in step 205 of reading, the temperature signal and the speed signal are read in. In the following step 210 of determining, the rotor current signal, the stator current signal, and the cooling signal are determined using the read-in signals. In this exemplary embodiment, step 210 of determining is also performed using a determination rule. The determination rule merely allows for an assignment of speed values ​​and temperature values ​​to values ​​of the magnitude of the rotor current and the magnitude of the stator current, by way of example.

[0042] In this exemplary embodiment, method 200 further includes a step 305 of activating active cooling, for example after outputting step 215. Active cooling is activated to additionally cool the stator.

[0043] Fig. 4 shows a diagram 400 illustrating a relationship between stator current flows Id, Iq and temperature values ​​Tir1, Tir2 according to an embodiment.

[0044] A first temperature value Tir1 corresponds to a first rotor temperature, and a second temperature value Tir2 corresponds to a second rotor temperature that differs from the first rotor temperature. A first vector 401 corresponds to a first stator current associated with the first temperature value Tir1, and a second vector 402 corresponds to a second stator current associated with the second temperature value Tir2, which differs from the first stator current.

[0045] In other words, at higher speeds, the rotor current is reduced depending on the rotor and stator temperatures to reduce rotor losses and allow for a reduction in cooling flow. The stator currents are then adjusted to maintain a constant torque.

[0046] Fig. Figure 5 shows a schematic representation of a vehicle 500 according to an exemplary embodiment. The vehicle 500 has an electric axle drive with an electric machine 100, as described, for example, with reference to the preceding figures. Electrical energy for operating the electric machine 100 is provided by a power supply device 502, which in one exemplary embodiment has the Fig.1. For example, the power supply device 502 provides a direct current for the rotor and an alternating current to the stator using a direct voltage provided by a battery, for example using a power converter. A shaft driven by the electric machine 100 is coupled directly or using a transmission device 506 to at least one wheel 508 of the vehicle 500. Thus, the vehicle 500 can be propelled using the electric machine 100. According to one embodiment, the electric axle drive comprises a housing in which the electric machine 100 and the transmission device 506 are arranged in an integrated manner. Reference symbol 100 electric machine 105 Stator 110 Rotor 115 Stator supply device 120 Rotor supply device 125 Cooling circuit 127 Pumping device 130 Device 135 Speed ​​signal 140 control unit 145 Temperature signal 150 Temperature recording device 155 Rotor current signal 160 Stator current signal 165 Cooling signal 170 active cooling 200 Method for operating an electrical machine of a vehicle designed as a separately excited DC motor 205 Step of reading 210 Step of Determination 215 Step of Spending 300 steps of capture 305 Activation step 400 diagram 401 first quantity of the stator current 402 second quantity of the stator current 500 vehicles 502 Energy supply facility 506 Gearbox device 508 bike Id stator current Iq counter-rotating stator current Tir1 first temperature value Tir2 second temperature value

Claims

[1] Method (200) for operating an electrical machine (100) designed as a separately excited DC motor for a vehicle (500), wherein the electrical machine (100) has a rotor (110) and a stator (105) as well as a cooling circuit (125) leading through the electrical machine (100), wherein the method (200) comprises the following steps (205, 210): Reading (205) a speed signal (135) representing a speed request for the electric machine (100) and a temperature signal (145) representing a temperature prevailing at the rotor (110); Determining (210) a rotor current signal (155) representing a magnitude of a rotor current for the rotor (110), a stator current signal (160) representing a magnitude of a stator current for the stator (105), and a cooling signal (165) representing a flow rate of cooling fluid through the cooling circuit (125) using the speed signal (135) and the temperature signal (145). [2] Method (200) according to claim 1, comprising a step (215) of outputting the rotor current signal (155) to a rotor supply device (120) in order to effect an adjustment of the rotor current to the magnitude of the rotor current determined in the determining step (210), and the stator current signal (160) to a stator supply device (115) in order to effect an adjustment of the stator current (Id, Iq) to the magnitude of the stator current (Id, Iq) determined in the determining step (210), and the cooling signal (165) to a pump device (127) of the cooling circuit (125) in order to effect an adjustment of the flow rate to the flow rate determined in the determining step (210). [3] Method (200) according to one of the preceding claims, wherein the step (210) of determining is carried out using a determination rule which enables an assignment of speed values ​​and temperature values ​​(Tir) to values ​​of the magnitude of the rotor current and the magnitude of the stator current (401, 402). [4] Method (200) according to one of the preceding claims, wherein in the step (210) of determining, a rotor current signal (155) is determined which represents a decrease in the magnitude of the rotor current, and a stator current signal (160) is determined which represents an increase in the magnitude of the stator current, and a cooling signal (165) is determined which represents a decrease in the flow rate, if in the step (205) of reading in a speed request and / or a temperature is read in which is above a predefined threshold value. [5] Method (200) according to one of the preceding claims, comprising a step (300) of detecting the temperature prevailing at the rotor (110) by means of a temperature detection device (150). [6] Method (200) according to one of the preceding claims, comprising a step (305) of activating an active cooling (170) to additionally cool the stator (105). [7] Device (130) which is arranged to carry out and / or control the steps (205, 210) of the method (200) according to one of the preceding claims in corresponding units. [8] Drive device for a vehicle (500), comprising an electrical machine (100) designed as a separately excited DC motor with a cooling circuit (125) and with a device (130) according to claim 7. [9] Electric axle drive for a vehicle (500) with at least one drive device and a transmission device (506), characterized by that the drive device is designed according to claim 8. [10] Vehicle (500) comprising a drive device according to claim 8 and / or an electric axle drive according to claim 9. [11] Computer program which is configured to execute and / or control the steps (205, 210) of the method (200) according to one of the preceding claims 1 to 3. [12] A machine-readable storage medium on which the computer program according to claim 11 is stored.

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