Method for controlling an electric machine of a working machine

Abstract

Method for controlling an electrical machine of a working machine, wherein the method comprises the following steps: (S1) Determining an operating requirement of the electrical machine; (S2) Operating the electric machine depending on the specific operating requirement in a recuperative mode in which electrical power is generated by introducing mechanical power into the electric machine, or in a drive mode in which the electric machine delivers mechanical power by absorbing electrical power; (S3) Determine an operating temperature which is the temperature of at least one element associated with the electrical machine; (S4) Reducing the maximum mechanical input power that can be introduced into the electric machine in recuperative operation when the specified operating temperature exceeds a predetermined recuperation limit temperature (T(R1)), and reducing the maximum mechanical output power that can be delivered by the electric machine in drive operation when the specified operating temperature exceeds a predetermined drive limit temperature (T(A1)); characterized in that the recuperation limit temperature (T(R1)) is lower than the drive limit temperature (T(A1)).

Description

Technical area

[0001] The present application relates to a method for controlling an electric motor of a working machine, which is intended to drive the working machine. The application further relates to a control device for controlling an electric motor of a working machine. State of the art

[0002] It is known to use an electric motor for the required drive in working machines. The electric motor then transmits its driving force to the machine's drive system and, if applicable, to other components of the machine, such as hydraulics, implements, and the like. In addition to providing drive power, the electric motors used can also perform energy recuperation by absorbing mechanical power and releasing electrical power. For example, during deceleration operation of the working machine, the mechanical power input into the electric motor can be fed back into an electrical energy storage device via the electric motor's generator function.

[0003] Electric machines incur losses during operation and generate heat. Elevated temperatures accelerate the aging of the machine's components, resulting in a reduction of output power from the machine's rated power, a process known as derating. Switching between regenerative and drive operation can also affect the driving performance of the machine.

[0004] The prior art, as described in DE 10 2013 224 841 A1, describes a method for determining the temperature of an electric machine. The temperature is determined in order to implement measures to limit the temperature of the electric machine.

[0005] Furthermore, control methods for controlling electrical machines of drive systems for vehicles are described in the prior art according to DE 10 2016 204 934 A1 and DE 10 2016 106 473 A1. Description of the invention

[0006] A method for controlling an electric machine of a working machine comprises the following steps: Determining an operating requirement of the electrical machine; Operating the electric machine depending on the specific operating requirement in a recuperative mode, in which electrical power is generated by introducing mechanical power into the electric machine, or in a drive mode, in which the electric machine delivers mechanical power by absorbing electrical power; Determining an operating temperature that is the temperature of at least one element associated with the electrical machine; Reducing the maximum mechanical input power that can be introduced into the electric machine in recuperative operation when the specified operating temperature exceeds a predetermined recuperation limit temperature, and reducing the maximum mechanical output power that can be delivered by the electric machine in drive operation when the specified operating temperature exceeds a predetermined drive limit temperature, wherein the recuperation limit temperature is lower than the drive limit temperature.

[0007] The electric machine used in the driven machine can be any electric machine designed to deliver mechanical power by receiving electrical power and vice versa. Therefore, any electric machine suitable for the driven machine can function as both a motor and an electric generator. The operating request for the electric machine can be generated by a requirement specified by the operator of the driven machine. In particular, the operating request can be generated by the position of the accelerator or brake pedal and then processed by the system. Alternatively, the operating request can be generated by an automated or semi-automated system.

[0008] The working machine can be any machine that can be driven by the electric machine. In particular, the working machine can have a drive system. This drive system can be based, for example, on a wheel drive, a track drive, or a similar mechanism. Furthermore, the working machine can have additional equipment, such as hydraulics or other working devices, which may be driven by the electric machine. The working machine can also have several electric machines that are interconnected. Alternatively, a separate electric machine can be provided for corresponding elements of the working machine.

[0009] The electric machine can be supplied with energy via an electrical converter. The electrical converter can be configured to operate the electric machine according to the requirements. Specifically, the electrical converter can operate the electric machine in drive mode, where it delivers mechanical power, and in recuperative mode, where the mechanical power absorbed by the electric machine is converted into electrical power. The electrical power can be fed into an energy storage device, such as a battery, via the electrical converter and stored there. Alternatively, the electrical power generated by the electric machine in recuperative mode can be fed partially or completely into an electrical load other than the electrical energy storage device.

[0010] When the electric machine is operated in recuperative mode, a torque can be generated on the electric machine which acts as a braking torque if the electric machine is linked to a drive system of the working machine.

[0011] When determining the operating temperature, which is the temperature of at least one element associated with the electrical machine, the temperature can be determined from the winding or a section of the winding. However, the operating temperature of the electrical machine can also be determined from another element, such as a rotor, stator, or other components of the electrical machine, as long as the measured temperature allows conclusions to be drawn about the operating temperature of the electrical machine. The determination of the operating temperature can be carried out by one or more temperature sensors that generate a corresponding signal.

[0012] When reducing the maximum mechanical input power that can be introduced into the electric machine during recuperation, or when reducing the maximum mechanical output power that can be delivered by the electric machine during drive operation, the electrical converter can be controlled accordingly to achieve the reduction. To reduce the maximum mechanical input power, the electrical power delivered by the electric machine can be reduced, thus making the torque acting against the rotation of the electric machine adjustable, and in particular, reducible. Likewise, the output power that can be delivered by the electric machine can be adjusted, and in particular reduced, by controlling the electrical converter, and in particular by controlling the electrical power input to the electric machine.

[0013] In one embodiment, the reduction of mechanical input power during recuperation is achieved according to a predetermined recuperation profile, depending on the operating temperature. Similarly, the reduction of mechanical output power during drive operation is achieved according to a predetermined drive profile, depending on the operating temperature. Both the recuperation and drive profiles can be stored in a characteristic map, which is stored in a memory device and can be retrieved. These recuperation and drive profiles establish functional relationships between the mechanical input power during recuperation and the mechanical output power during drive operation, respectively, as a function of the electric machine's operating temperature. This functional relationship can be determined empirically.The functional relationship can alternatively be predetermined based on a formulaic relationship. Alternatively, the functional relationship can also be predetermined in the form of a table.

[0014] In one embodiment, the recuperation curve and the drive curve are each at least sectionally linear as a function of the operating temperature. In particular, the recuperation curve and the drive curve represent functions that decrease with increasing operating temperature. The recuperation curve provides a so-called derating factor, dependent on the specific operating temperature, which reduces the rated mechanical power that can be absorbed by the electric machine. Similarly, the drive curve provides a so-called derating factor, dependent on the specific operating temperature of the electric machine, which reduces the rated mechanical power that can be delivered by the electric machine. The derating factors used are provided with values ​​ranging from 1 to 0 and from 100% to 0%, respectively.

[0015] In one embodiment, the recuperation profile can have a steeper gradient than the drive profile. In this embodiment, after exceeding the recuperation limit temperature, the mechanical power absorbed by the electric machine is reduced more significantly with a further increase in the operating temperature than the mechanical power output by the electric machine after exceeding the drive limit temperature. Thus, in this embodiment, a further increase in the temperature of the electric machine during recuperation operation is taken into greater account than during drive operation.

[0016] In one embodiment, recuperation can be deactivated when the operating temperature reaches a predetermined recuperation cut-off temperature. Furthermore, drive operation can be deactivated when the operating temperature reaches a predetermined drive cut-off temperature. The recuperation cut-off temperature is higher than the recuperation limit temperature. Similarly, the drive cut-off temperature is higher than the drive limit temperature. Upon reaching the recuperation cut-off temperature, a derating factor of 0 or 0% can be set, thus reducing the mechanical power absorbed by the electric machine to 0. Similarly, upon reaching the drive cut-off temperature, the derating factor can be set to 0 or 0%, thus reducing the mechanical power output of the electric machine to 0.The aforementioned function serves to protect the electric machine, and the drive shutdown temperature and the recuperation shutdown temperature are set as limit temperatures at which further operation would lead to excessive impairment or damage to the electric machine.

[0017] In one embodiment, the predetermined drive shutdown temperature is set higher than the predetermined recuperation shutdown temperature. In this embodiment, recuperation operation is therefore switched off at a lower temperature than drive operation.

[0018] In one embodiment, the recuperation profile and the drive profile are variable to reduce power consumption depending on other operating parameters of the machine. The recuperation profile and the drive profile can deviate from the optionally linear profiles. Furthermore, the slope, curvature, or other shape of the recuperation profile and the drive profile can be variable. The operating parameters of the machine can include the state of charge of the electrical energy storage device, the operating state of other implements, the operating time in a predetermined operating state, or similar parameters.

[0019] In one embodiment, the predetermined temperatures, in particular the drive limit temperature, the recuperation limit temperature, the drive cut-off temperature, and the recuperation cut-off temperature, are variable depending on other operating parameters of the machine. These operating parameters can include those already mentioned above.

[0020] The method according to the present embodiments can preferably be carried out repeatedly, in particular cyclically, so that the operating temperature can be detected in a suitable manner and the corresponding control interventions can be made appropriately.

[0021] In one embodiment, a braking torque for the driven machine can be generated during recuperation operation, depending on a braking torque demand. If the maximum mechanical input power decreases due to exceeding the recuperation limit temperature, a mechanical braking device can also be operated if the braking torque generated by the electric machine is less than the braking torque demand. The braking torque demand can be derived from the actuation of a brake pedal. Alternatively, the braking torque demand can be derived from an automatic or semi-automatic control system of the driven machine. The braking torque demand can represent the required deceleration of the driven machine during operation.In this embodiment, a deceleration of the working machine can thus be generated based on the braking torque requirement by combining the braking torque of the electric machine resulting from recuperation mode and a braking torque generated by a mechanical braking device to produce a total braking torque. Furthermore, in this embodiment, the mechanical braking device can be equipped with a control unit that, based on control signals, actuates the mechanical braking device so that the required braking torque can be generated by the mechanical braking device.

[0022] In one embodiment, a braking torque for the driven machine can be generated during recuperation operation, depending on a braking torque demand. A gearbox provided on the electric machine, with at least two gear ratios, is controlled according to the thermal load of the electric machine such that the braking torque generated by the electric machine is closest to the braking torque demand. In this embodiment, the gearbox can be located between an output element of the electric machine and an input element of the drive system of the driven machine. This design allows the rotational speed of the electric driven machine to be varied in a predetermined operating situation due to the variability of the gear ratio of the gearbox.This embodiment allows the electric machine to be set at a speed suitable for recuperative operation. This approach reduces further temperature increases in the electric machine. Furthermore, the braking torque generated by the electric machine during recuperation can be increased. This design optimizes energy recovery during recuperation while simultaneously minimizing the operation of the mechanical braking system. The transmission can be a stepped transmission with at least two gear ratios. Alternatively, the transmission can be a continuously variable transmission (CVT) in which the gear ratios are continuously variable.

[0023] According to another aspect, a control device for an electric machine of a working machine has input and output interfaces for receiving and sending measurement and control signals, as well as a storage device. The control device is configured to determine an operating temperature, which is the temperature of at least one element associated with the electric machine, and to compare it with values ​​stored in the storage device. Furthermore, the control device is configured to control the operation of the electric machine in at least a recuperative mode and a drive mode, wherein the control device is configured to execute the method according to one or more of the aforementioned embodiments.

[0024] In one embodiment, the control device can be integrated into the global control unit of the machine. Alternatively, the control device can be a separate element that is linked to the global control unit of the machine via a signal connection. The control device can be connected to an automatic or semi-automatic system. The input and output interfaces can be connected to sensors and actuators to acquire measurable values ​​and to actuate appropriate actuators of the machine. The control device can be connected via the input interface to a temperature sensor to determine the temperature of at least one element associated with the electric machine. Furthermore, the control device can be connected via the output interface to an electrical transducer to control the operation of the electric machine.

[0025] According to the embodiments described above, the electric motor of the driven machine can operate in recuperative mode during deceleration and in drive mode during acceleration. Due to its design, the driven machine can frequently switch between recuperative and drive modes. Particularly when switching from recuperative to drive mode, the concept described above prevents a drop in power output upon immediate resumption of drive operation, especially when the electric motor's temperature increases. This is because the described design of the method allows for a greater mitigation of temperature increases in the electric motor during recuperative mode by reducing the electrical power input when the temperature rises, compared to drive mode.Thus, in the drive operation following the recuperative operation, the working machine can be operated with the lowest possible loss of power or tractive force. Short description of the drawings Fig. Figure 1 shows in a schematic diagram the process steps of an embodiment of the process; Fig. Figure 2 shows a diagram illustrating the dependence between derating factors and the operating temperature of the electric machine in one embodiment. Detailed description of embodiments

[0026] One embodiment of the method is described below with reference to the drawings. In the Fig. Diagram 1 illustrates a process flow that includes the necessary steps for controlling the electric machine according to the present embodiment. The method is applied to a machine that is not shown in the drawings and is briefly explained below using an example.

[0027] The machine, in an embodiment to which the method is applicable, is exemplified as a wheel loader. The wheel loader has wheels that serve to drive it. The wheels of the wheel loader are driven by an electric motor, which is connected to the wheels via a multi-stage transmission and other necessary drivetrain components. The wheel loader is accelerated by pressing an accelerator pedal and decelerated by pressing a brake pedal. The electric motor serves both to propel and decelerate the wheel loader.

[0028] In the present embodiment, the wheel loader has an electrical converter that is connected on one side to the electric motor and on the other side to an electrical energy storage device designed as a rechargeable battery. The electrical converter is configured to control the electric motor so that the electric motor can be operated at a predetermined operating point. The machine also has a control device that is equipped with input and output interfaces and communicates, in particular, with the electrical converter. Furthermore, the control device is connected to various sensors, including, in particular, a temperature sensor that detects the temperature of a winding of the electric motor as the operating temperature, a sensor for detecting the deflection of an accelerator pedal, and a sensor for detecting the deflection of a brake pedal.

[0029] The wheel loader according to the present embodiment further comprises a mechanical braking system which, in this embodiment, can brake the wheels of the wheel loader via a hydraulic system. The braking system of the wheel loader is designed such that the braking force generated by the mechanical braking system can be controlled by the control device according to predetermined parameters.

[0030] The control device is thus designed to control, on the one hand, the mechanical braking system of the wheel loader and, on the other hand, the electrical converter and thus the operation of the electric machine on the basis of input signals and other information stored in a memory device of the control device.

[0031] According to the present embodiment, the wheel loader has additional elements that can be driven by the electric motor, such as a lifting frame and a power take-off. The wheel loader also has a global control unit into which the aforementioned control device is integrated. Therefore, the control device, in which the method described below is carried out, has access to further information in the form of control signals and data necessary for the operation of the wheel loader.

[0032] The Fig. The procedure shown in step S1 starts with the determination of an operating requirement for the electric motor of the wheel loader. For this purpose, the aforementioned sensor for detecting the deflection of the accelerator pedal is queried. Additionally, the corresponding sensor for detecting the deflection of the brake pedal of the wheel loader is queried. The available signals are processed in the control device.

[0033] In the subsequent step S2, the electric machine is controlled by activating the electrical converter based on the specified operating requirement. In the present embodiment, recuperative operation is initiated when it is detected that the brake pedal is being deflected. Depending on the degree of brake pedal deflection, the electrical converter is controlled so that the electric machine generates a corresponding braking torque. This braking torque decelerates the wheel loader. The mechanical power absorbed by the electric machine is converted into electrical power in generator mode and fed into the energy storage device via the electrical converter.

[0034] When step S2 detects that the accelerator pedal is being pressed, the electric converter is controlled in such a way that the electric machine generates mechanical power by absorbing electrical power from the energy storage device and delivering it to the wheels of the wheel loader. In this situation, the wheel loader accelerates. The acceleration depends on the degree of travel of the accelerator pedal, which is detected by the corresponding sensor and transmitted to the control unit for further processing.

[0035] In step S3, the operating temperature of the winding of the electric machine is measured. For this purpose, the aforementioned temperature sensor is used, which feeds its corresponding signals into the control device.

[0036] In step S4, a distinction is made between recuperative operation and drive operation of the electric machine. First, the procedure in recuperative operation is explained.

[0037] If an operational request exists to decelerate the wheel loader, the electric machine operates in regenerative mode. The winding temperature of the electric machine, measured in step S3, is processed by the control unit. Various data, and in particular a predetermined regenerative limit temperature T(R1), are stored in the control unit's memory. In step S4, the measured operating temperature of the electric machine is compared with the regenerative limit temperature T(R1) during regenerative operation. If step S4 determines that the operating temperature of the electric machine has exceeded the regenerative limit temperature T(R1), the maximum mechanical input power of the electric machine is reduced during regenerative operation. This reduction is achieved by controlling the electrical converter.

[0038] During drive operation, in which the electric machine delivers mechanical power, the operating temperature of the electric machine is also measured and processed in the control device. If, in step S4, it is determined that the operating temperature of the electric machine has exceeded the predetermined drive limit temperature T(A1), the maximum mechanical output power of the electric machine during drive operation is reduced by controlling the electrical converter.

[0039] To reduce the maximum mechanical input power in recuperation mode and the maximum mechanical output power in drive mode, a maximum rated power in recuperation mode and a maximum rated power in drive mode are assumed. Based on the in Fig. In the schematic diagram shown in Figure 2, a derating factor DF is determined for recuperative operation and for drive operation.

[0040] As in Fig. As shown in Figure 2, the wheel loader's electric machine operates at 100% of its rated power at low temperatures, both in recuperation and drive modes. This represents the maximum power for which the electric machine is designed. During operation, the electric machine generates heat in both recuperation and drive modes. This heat generation causes the temperature inside the electric machine to rise, which, as shown above, is detected by the temperature sensor on the winding. As shown in Fig. As shown in Figure 2, the schematically represented diagram defines the recuperation limit temperature T(R1), at which the mechanical power absorbed by the electric machine during recuperation is gradually reduced depending on the operating temperature. Furthermore, in Fig. 2. It is evident that a drive limit temperature T(A1) is provided, at which the mechanical power output of the electric machine is reduced depending on the operating temperature. As shown in the diagram of Fig. As can be seen in Figure 2, the recuperation limit temperature T(R1) is set lower than the drive limit temperature T(A1). Therefore, derating is initiated at a lower temperature during recuperation than during drive operation. Furthermore, the diagram shows that... Fig. 2. It is evident that the gradient for reducing the mechanical power absorbed by the electric machine in recuperative operation is steeper than the gradient for reducing the mechanical power output by the electric machine in drive operation.

[0041] Therefore, in step S4, once the recuperation limit temperature T(R1) is reached in recuperation mode or the drive limit temperature T(A1) is reached in drive mode, the power output of the electric machine is reduced to prevent a further increase in the electric machine's temperature. Furthermore, this procedure prevents the electric machine's components from aging due to temperature influences.

[0042] The concept of the present method also enables optimized operation of the wheel loader, which is typically used in frequent switching between recuperation and drive modes. Specifically, when the wheel loader is in recuperation mode, i.e., decelerating, a certain degree of power derating is performed after the recuperation limit temperature is exceeded. During the subsequent and usually immediate switch to drive mode, sufficient drive power is available because the derating in drive mode begins with a higher drive limit temperature T(A1) than the recuperation limit temperature T(R1) and exhibits a shallower gradient than in recuperation mode. This prevents the operator from experiencing a perceived drop in power when switching from recuperation to drive mode.

[0043] As further stated in Fig. As shown in Figure 2, the derating factor DF reduces the power of the electric machine linearly from 100% of its rated power after reaching the recuperative temperature T(R1) in recuperative operation, as the operating temperature continues to rise. Upon reaching a recuperative shutdown temperature T(R2), recuperative operation is completely switched off, and in this case, the power of the electric machine is 0% of its rated power.

[0044] As also in Fig. As shown in Figure 2, the derating factor DF reduces the power of the electric machine linearly from 100% of its rated power after the drive temperature T(A1) is reached during drive operation, as the operating temperature continues to rise. Upon reaching a drive shutdown temperature T(A2), the drive operation is completely shut down, and in this case, the power of the electric machine is 0% of its rated power.

[0045] In Fig.Figure 2 shows that the gradient at which the derating factor decreases with increasing operating temperature is set steeper for recuperation mode than for drive mode. This design allows for further optimization of the wheel loader's operation.

[0046] In one embodiment, the wheel loader has a multi-stage transmission. The transmission is located in the power transmission path between the electric motor and the drive system or the wheels of the wheel loader. In this embodiment, the speed of the electric motor can be adjusted during recuperation by changing the gear ratio via appropriate control signals from the control unit. For example, if a high braking torque is required, the transmission's gear ratio can be set to increase the speed of the electric motor, thus providing a higher braking torque. Furthermore, the speed of the electric motor can be controlled based on the operating temperature to prevent excessive temperature increases. The transmission can be controlled similarly during drive operation. Reference sign S1 Determining an operational requirement S2 Operating the electric machine S3 Determining an operating temperature S4 Reducing the maximum mechanical input / output power T(R1) Recuperation limit temperature T(A1) Drive limit temperature T(R2) Recuperation shutdown temperature T(A2) Drive shutdown temperature DF Derating Factor

Claims

[1] Method for controlling an electrical machine of a work machine, the method comprising the following steps: (S1) determining an operating requirement of the electrical machine; (S2) Operating the electrical machine depending on the specific operating requirement in a recuperative mode in which electrical power is generated by introducing mechanical power into the electrical machine, or in a drive mode in which the electrical machine outputs mechanical power by absorbing electrical power; (S3) determining an operating temperature which is the temperature of at least one element associated with the electric machine; (S4) reducing the maximum mechanical input power that can be introduced into the electric machine in recuperative operation if the determined operating temperature exceeds a predetermined recuperation limit temperature (T(R1)), and reducing the maximum mechanical output power that can be delivered by the electric machine in drive operation if the determined operating temperature exceeds a predetermined drive limit temperature (T(A1)); characterized by that the recuperation limit temperature (T(R1)) is lower than the drive limit temperature (T(A1)). [2] Method according to claim 1, characterized bythat the reduction of the mechanical input power in recuperative operation takes place as a function of the specific operating temperature with a predetermined recuperation curve and the reduction of the mechanical output power in drive operation takes place as a function of the specific operating temperature with a predetermined drive curve. [3] Method according to claim 2, characterized by that the recuperation curve and the drive curve are each, at least in sections, linearly decreasing curves depending on the operating temperature. [4] Method according to claim 3, characterized by that the recuperation curve has a steeper gradient than the drive curve. [5] Method according to one of the preceding claims, characterized bySwitching off the recuperative operation when the determined operating temperature reaches a predetermined recuperation switch-off temperature (T(R2)), and switching off the drive operation when the determined operating temperature reaches a predetermined drive switch-off temperature (T(A2)). [6] Method according to claim 5, characterized by that the predetermined drive switch-off temperature (T(A2)) is higher than the predetermined recuperation switch-off temperature (T(R2)). [7] Method according to one of claims 2-6, characterized by that the recuperation process and the drive process for reducing power are variable depending on other operating parameters of the working machine. [8] Method according to one of claims 1-7, characterized by that the predetermined temperatures (T(R1); T(A1); T(R2); T(A2)) are variable depending on other operating parameters of the working machine. [9] Method according to one of claims 1-8, characterized bythat in recuperative operation, a braking torque is generated for the working machine depending on a braking torque requirement, wherein when the maximum mechanical input power is reduced due to the recuperation limit temperature (T(R1)) being exceeded, a mechanical braking device is additionally operated if the braking torque generated by the electric machine is lower than the braking torque requirement. [10] Method according to one of claims 1-9, characterized by that in recuperative operation a braking torque is generated for the working machine as a function of a braking torque requirement, wherein a transmission provided on the electric machine with at least two transmission ratios is controlled as a function of the thermal load on the electric machine in such a way that the braking torque generated by the electric machine is closest to the braking torque requirement. [11] Control device for an electrical machine of a work machine with input and output interfaces for receiving and outputting measurement or control signals and a memory device, wherein the control device is set up to determine an operating temperature, which is the temperature of at least one element assigned to the electrical machine, and to compare it with values stored in the memory device, and to control the operation of the electrical machine at least in a recuperative mode and a drive mode, wherein the control device is set up to carry out the method according to one of the preceding claims.

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