Method for controlling the operation of an electric machine

Abstract

Method for controlling the operation of an electric machine (3) of a motor vehicle (1), wherein an operating parameter of the electric machine (3), in particular a current and / or a torque, is limited in an overload range in which an actual temperature of the electric machine (3) exceeds a limit temperature, wherein the actual temperature is determined based on a thermal model of the electric machine (3) and the limit temperature is determined based on at least one driving parameter describing the driving behavior of the motor vehicle (1).

Description

[0001] The invention relates to a method for controlling the operation of an electric machine of a motor vehicle, wherein an operating parameter of the electric machine, in particular a current and / or a torque, is limited in an overload range in which an actual temperature of the electric machine exceeds a limit temperature.

[0002] Methods for controlling the operation of electric motors in motor vehicles are generally known from the prior art. Typically, the operating parameters of the electric motor, such as the current supplied to the electric motor or the torque output or to be provided by the electric motor, are controlled or regulated to drive the motor vehicle in a specific operating state. During operation, the actual temperature of the electric motor can be monitored to ensure that it does not exceed a certain temperature, thus guaranteeing efficient operation and preventing damage to its components. A technique known as "derating" is used for this purpose, in which the operating parameters of the electric motor are limited if a critical temperature is exceeded.For example, the torque or current supplied to the electric machine is limited when the limit temperature is exceeded, so that a further increase in the actual temperature of the electric machine, in particular an overload of the electric machine, can be ruled out.

[0003] It is known from the prior art to perform such "derating," particularly linearly, when the specified limit temperature is exceeded. This means that the current operating state of the electric machine is not taken into account when limiting the operating parameters; that is, a limitation is applied regardless of the current or future operating strategy of the vehicle. If the actual temperature remains relatively constant within the range of the limit temperature, such that it alternately exceeds and then quickly falls below the limit temperature (possibly due to derating), this leads to fluctuations in the operation of the electric machine, particularly in the available torque. This is detrimental to the operation and the driving comfort of the user.The described derating process thus represents a compromise, ensuring that damage to components of the electrical machine is reliably prevented, but avoiding an overly conservative approach in order to avoid unnecessarily losing potential of the electrical machine.

[0004] The invention is based on the objective of providing an improved method for controlling the operation of an electric machine of a motor vehicle, in which, in particular, the limitation of the operating size is improved.

[0005] The problem is solved by a method with the features of claim 1. Advantageous embodiments are the subject of the dependent claims.

[0006] As described at the outset, the invention relates to a method for controlling the operation of an electric machine of a motor vehicle, wherein an operating parameter of the electric machine, in particular a current and / or a torque, is limited in an overload range in which the actual temperature of the electric machine exceeds a limit temperature. In other words, the method performs a so-called "derating" in which the operation of the electric machine is limited so that no thermal overload can occur.

[0007] The invention is based on the understanding that the actual temperature is determined using a thermal model of the electric machine, and the limit temperature is defined based on at least one driving parameter describing the vehicle's behavior. The invention thus proposes, firstly, to use a thermal model to determine the actual temperature of the electric machine. Parameters of the electric machine are input into the thermal model, for example, operating parameters or temperature parameters of selected temperature-critical components of the electric machine. The thermal model uses these input parameters to determine the actual temperature of the electric machine. In other words, the input parameters are fed into the thermal model, which then outputs the actual temperature as a parameter.

[0008] In addition, the described method incorporates the vehicle's driving behavior through the driving parameter. By defining the limit temperature as a function of the driving parameter, the vehicle's driving behavior, and in particular the driving style or strategy of the vehicle's user, is integrated into the method. This eliminates the need to specify a fixed temperature, regardless of the driving situation, above which derating is always performed in the same way. Instead, it is possible to define the limit temperature based on the vehicle's driving behavior. This allows for a higher limit temperature in more conservative driving styles or situations, in order to better utilize the thermal potential of the electric motor.In driving situations where a high load on the electric machine is expected, for example due to a sportier driving style, higher recuperation performance and the like, it is possible to set the limit temperature lower in order to be able to react to thermal loads at an early stage.

[0009] By incorporating driving behavior, the so-called "hopping" of the electric machine between normal operation and derating can be prevented. This is because the current driving situation can be taken into account, and thus, in situations where the actual temperature fluctuates around a certain temperature close to the limit temperature, the limit temperature can be set based on the driving parameter in such a way that the fluctuating actual temperature does not lead to a constant switching between derating and normal operation. In other words, the method described herein proposes, firstly, to execute the limitation of the operating parameter based on knowledge of the actual temperature of the electric machine, and secondly, to incorporate knowledge or understanding of the vehicle's driving behavior—i.e., the vehicle's operating mode and the driver's behavior—into the execution of the limitation, i.e., the "derating," by setting the limit temperature.

[0010] The described method can be further developed such that at least one driving parameter is determined based on a driving profile of the driver of the motor vehicle, in particular based on at least one current or historical movement parameter. The driver's driving profile can reflect the driver's driving style, for example, the way the driver travels a particular section of road or how the driver usually operates the motor vehicle. For example, the driving profile can include the use of the accelerator pedal, in other words, how much the driver demands from the electric motor during operation of the motor vehicle.

[0011] The driving profile can define or incorporate driving behavior based on factors such as lateral acceleration, speed, longitudinal acceleration, recuperation, and the like, so that the driving parameter can subsequently describe the vehicle's behavior. Determining the driving profile can be based on historical data, i.e., how the driver has driven the vehicle in the past, for example, on a similar or the same stretch of road. It is also possible for the driving profile to reflect the current state, such as how the driver is currently operating the vehicle. Incorporating driving behavior makes it possible, in particular, to increase the availability of the electric motor and avoid unnecessary limitations on its operating range. This allows the electric motor's power ranges to be extended and its thermal potential to be utilized more effectively.

[0012] At least one driving parameter can be determined based on a test track run and / or current or expected recuperation power and / or prior route data. As previously described, it is also possible to determine the driving parameter for the current operating state, for example, the current speed of the driver or the power output the driver is drawing from the electric motor. The driving parameter can be determined, for example, by means of a test track run. This means that a specific route can be designated as the test track, based on which the driving profile or at least one driving parameter can be defined. During this process, lateral accelerations, longitudinal accelerations, speeds, and similar parameters can be recorded while driving along the test track to determine how the electric motor is stressed.

[0013] Based on the test track run, driving parameters for similar or different routes can be determined, for example, based on curve radii, expected speeds, gradients, and the like. The limit temperature can then be adjusted accordingly, depending on whether the route to be driven will place a higher or lower load on the electric motor. Furthermore, recuperation power can be included, as this also represents a load on the electric motor. In both cases, upcoming route data can be considered, for example, from navigation data, in particular regarding gradients, curve radii, speeds, and the like that lie ahead and must therefore be traversed.Accordingly, the limit temperature can be adjusted depending on the requirements for the electric machine, for example, whether it is operated on an incline following the current operating state, whether it has to provide recuperation power, or whether the driver is driving in a sporty manner and / or this is expected. All the parameters described can be taken into account, and an average value can be calculated as a driving parameter, which can then be used as the basis for setting the limit temperature.

[0014] Furthermore, at least one driving parameter can be determined based on the torque to be provided by the electric machine and / or the current to be supplied to the electric machine. This offers the possibility of determining the driving parameter without prediction, for example, independently of the previously described determination of the driving parameter based on the test track drive, the expected recuperation power, or route data. In particular, it is possible to monitor which torque is to be provided by the electric machine in the current operating state or which electric current is to be supplied to the electric machine or is currently being supplied. This therefore includes the driving behavior of the vehicle, since the driver ultimately indirectly influences the current supplied to the electric machine via the accelerator pedal position or the setting of the vehicle speed.This determines the torque output of the electric motor. Depending on the driver's requirements for the electric motor, the limit temperature can be adjusted to prevent overloading and avoid unnecessary limitations on the operating range.

[0015] As described, the thermal model for determining the actual temperature is supplied with at least one input parameter. According to one embodiment of the method, the thermal model can determine the actual temperature of at least one main component of the electric machine based on this input parameter. In other words, the current operating point of the electric machine can be determined based on one or more input parameters, such as the temperatures, of the main components, i.e., the critical components, of the electric machine. The rotor, stator, and inverter of the electric machine are considered to be the main components.The thermal model can then describe the physical processes and thus output an actual temperature for the electric machine, which can be compared with the limit temperature to determine whether the electric machine is operating in an overload range where its operating size must be limited. Furthermore, the thermal model can make predictions, i.e., incorporate the expected development of the actual temperature, for example, based on thermal inertia, current or expected temperatures, temperature gradients, heat transfer, power losses, or other parameters of the main components of the electric machine.

[0016] Furthermore, the method can be designed so that the thermal model determines the actual temperature based on at least one heat transfer point between at least two main components of the electric machine. Such heat transfer points can also be referred to as "nodes," allowing the thermal model to represent the fundamental physical behavior of the electric machine with respect to temperature or temperature development. In this context, the temperature-critical components are considered the main components, so that the overall actual temperature of the electric machine can be determined based on their actual temperature or temperature development. Determining the actual temperature can also be based, for example, on the power losses of the individual main components, taking into account heat transfers, thermal inertia, temperature gradients, and the like, as described.

[0017] The method can further provide for the thermal model to determine the actual temperature for a current operating state and / or for at least one operating state preceding it in the direction of travel. As described, a current analysis of the actual temperature can be performed based on the input parameters described. For example, the actual temperatures, heat transfers, and the like, as previously described, can be fed into the thermal model so that the thermal model outputs the actual temperature for the electric machine. Likewise, the actual temperature can be predicted, i.e., the actual temperature for at least one preceding operating state, i.e., an operating state that follows or is immediately adjacent to the current operating state, can be determined. This makes it possible to incorporate changes in the actual temperature, such as temperature increases or decreases, into the thermal model.If the thermal model indicates, for example, a cooling of the electric machine, the limiting temperature can be raised if necessary. Conversely, if the thermal model indicates a continuous heating of the electric machine, the limiting temperature can be lowered if necessary.

[0018] In addition to the method, the invention relates to a control device for controlling the operation of an electric machine of a motor vehicle, wherein the control device is configured to limit an operating parameter of the electric machine, in particular a current and / or a torque, in an overload range in which an actual temperature of the electric machine exceeds a limit temperature, wherein the control device is configured to determine the actual temperature based on a thermal model of the electric machine and to define the limit temperature based on at least one driving parameter describing the driving behavior of the motor vehicle.

[0019] The invention further relates to a drive arrangement comprising an electric machine and a previously described control device. The invention also relates to a motor vehicle comprising such a drive arrangement and / or a previously described control device. The drive arrangement can, for example, be configured as an electric axle drive of the motor vehicle. The control device is configured to execute the method with all previously described details, advantages, and features. All advantages, details, and features described with respect to the method are fully transferable to the control device, the drive arrangement, and the motor vehicle.

[0020] The invention is explained below with reference to exemplary embodiments and the figures. The figures are schematic representations and show: Fig. 1. A schematic diagram of a motor vehicle; and Fig. 2. A flowchart of a procedure for controlling the operation of an electric machine of a motor vehicle.

[0021] Fig. Figure 1 shows a schematic diagram of a motor vehicle 1, which has a drive arrangement 2 comprising an electric machine 3 and a control device 4. The electric machine 3 is designed, in particular, as a traction drive for the motor vehicle 1, specifically as an electric axle drive. The control device 4 is designed, in particular, to control or regulate the operation of the electric machine 3. For example, the electric machine 3 can be operated by supplying it with a specific electric current, such that the electric machine 3 outputs a requested torque to drive the motor vehicle 1.

[0022] The control device 4 is further configured for so-called "derating," meaning that if the electric machine 3 enters an overload range, its operating parameters, i.e., the current or torque, are limited to reliably prevent overloading. The overload range of the electric machine 3 is defined, for example, by a limit temperature. Depending on the actual temperature of the electric machine 3, the control device 4 can perform the limitation, i.e., the "derating."

[0023] A schematic sequence of the procedure for operating the electric machine 3 of the motor vehicle 1, which can be carried out by the control device 4, is shown in Fig.Figure 2 illustrates this. The process can, for example, start in a block 5, where the actual temperature of the electric machine 3 is determined. For this purpose, various or at least one input parameter can be collected, which can relate to at least one main component of the electric machine 3, for example, the stator, the rotor, or an inverter of the electric machine 3. The at least one input parameter can be fed into a thermal model in a block 6, which can output the actual temperature of the electric machine 3 based on the at least one input parameter. The actual temperature of the electric machine 3 can be output for a current operating state or for a future operating state, i.e., current or predicted.

[0024] Subsequently or simultaneously, the limit temperature can be set in a block 7, namely based on a driving parameter that describes the driving behavior of the vehicle 1. The driving parameter thus describes, in particular, how the vehicle 1 is operated, i.e., driven, specifically whether a conservative or sporty driving style is used, whether the vehicle 1 is driven on a slope or an incline, and the like. The driving parameter can include further individual parameters, such as curve radii, longitudinal accelerations, lateral accelerations, recuperation power, and the like. It is also possible for the driving parameter to be set based on the operating variable, for example, accelerator pedal input by the driver of the vehicle 1.In other words, the driving parameter can be determined by the control device 4 monitoring which current is supplied or is to be supplied to the electric machine 3, or which torque is provided or is to be provided by the electric machine 3, i.e., is called upon.

[0025] Subsequently, in block 8, a decision is made based on the actual temperature of the electric machine 3, determined using the thermal model, and the defined limit temperature, which was determined based on the driving parameter, as to whether a limitation of the operating size of the electric machine 3 is necessary. If the limit temperature is exceeded by the actual temperature, this leads to a limitation of the operating size, as described above. If the limit temperature is higher than the actual temperature, a limitation of the operating size is not necessary.

[0026] Advantageously, the described method can incorporate the driver's or vehicle's driving behavior by not setting the limit temperature as fixed for all operating conditions, but rather by defining it as a function of the driving parameter. This allows for better utilization of the thermal potential of the electric machine 3, i.e., in particular, avoids unnecessary limitations on the operating parameters. Specifically, fluctuations in the electric machine 3 can also be avoided, for example, when its temperature oscillates or fluctuates within a derating temperature range. In this case, the limit temperature in the method can be set such that if the change in the actual temperature due to driving behavior is only minor, the limit temperature is not exceeded, for example, by setting the limit temperature above the fluctuation range.

[0027] The described procedure can be carried out continuously or at fixed time intervals to ensure that the actual temperature remains below the limit temperature or, if the limit temperature is exceeded, that the operating size can be limited to prevent overheating of the electric machine 3.

[0028] As described, the control device 4 is designed to execute the described procedure. Since the control device 4 is part of the motor vehicle 1, the preceding description is fully transferable to the motor vehicle 1 or the drive arrangement 2 of the motor vehicle 1. Reference sign 1 motor vehicle 2 Drive arrangement 3 electric machine 4 Control unit 5-8 Block

Claims

[1] Method for controlling the operation of an electrical machine (3) of a motor vehicle (1), wherein an operating variable of the electrical machine (3), in particular a current and / or a torque, is limited in an overload range in which an actual temperature of the electrical machine (3) exceeds a limit temperature, characterized by that the actual temperature is determined based on a thermal model of the electric machine (3) and the limit temperature is set based on at least one driving parameter describing a driving behavior of the motor vehicle (1). [2] Method according to claim 1, characterized by that the at least one driving parameter is determined based on a driving profile of a driver of the motor vehicle (1), in particular based on at least one current or historical movement parameter. [3] Method according to claim 1 or 2, characterized bythat the at least one driving parameter is determined based on a test route drive and / or a current or expected recuperation performance and / or upcoming route data. [4] Method according to one of the preceding claims, characterized by that the at least one driving parameter is determined based on a torque to be provided by the electric machine (3) and / or a current to be supplied to the electric machine (3). [5] Method according to one of the preceding claims, characterized by that the thermal model determines the actual temperature based on at least one input parameter of at least one main component of the electrical machine (3). [6] Method according to one of the preceding claims, characterized by that the thermal model determines the actual temperature based on at least one heat transfer of at least two main components of the electrical machine (3). [7] Method according to one of the preceding claims, characterized by that the thermal model determines the actual temperature for a current operating state and / or for at least one previous operating state. [8] Control device (4) for controlling the operation of an electrical machine (3) of a motor vehicle (1), wherein the control device (4) is designed to limit an operating variable of the electrical machine (3), in particular a current and / or a torque, in an overload range in which an actual temperature of the electrical machine (3) exceeds a limit temperature, characterized by that the control device (4) is designed to determine the actual temperature based on a thermal model of the electric machine (3) and to set the limit temperature based on at least one driving parameter describing a driving behavior of the motor vehicle (1). [9] Drive arrangement (2) comprising an electric machine (3) and a control device (4) according to the preceding claim. [10] Motor vehicle (1) comprising a drive arrangement (2) according to the preceding claim and / or a control device (4) according to claim 8.

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