Method and device for controlling an inverter of an electric machine in a drive train of a vehicle

Abstract

The invention relates to a method for controlling an inverter (2) between an electric battery (1) and an electric machine (3) arranged in a drive train (4) of a vehicle, in order to bring about a desired drive torque (Tqprop) in the drive train (4) by means of the electric machine (3). In order to eliminate battery operation problems that often exist, for example at cold ambient temperatures, the invention proposes that, in the event of a desired drive torque (Tqprop) lying above a specified threshold torque (Tqth) and a temperature (Tbat) of the electric battery (1) lying below a specified threshold temperature (Tbatth), a control mode is provided in which a torque (Tq) is generated by means of the electric machine (3), which torque rapidly changes back and forth between a positive torque (Tq+) lying above the desired drive torque (Tqprop) and a negative torque (Tq-) lying below the desired drive torque (Tqprop) such that the desired torque (Tqprop) is produced on average over time. Furthermore, the invention relates to a corresponding control device (10). The invention thus advantageously makes it possible, for example, to start up a corresponding drive system even at cold ambient temperatures.

Description

[0001] 202400509

[0002] 1

[0003] Description

[0004] Method and device for controlling an inverter of an electric machine in a vehicle drive train

[0005] The present invention relates to a method for controlling an inverter according to the preamble of claim 1 and to a device for controlling an inverter according to the preamble of claim 9.

[0006] Such generic methods and devices are known from the prior art and accomplish the control of an inverter between an electric battery and an electric machine arranged in a vehicle's drive train in order to effect a desired drive torque ("target drive torque") in the drive train by means of the electric machine.

[0007] The invention can therefore be used in particular, for example, in the field of battery electric vehicles (BEVs), although the invention could also be used in other types of vehicles such as hybrid electric vehicles (HEVs).

[0008] It is also known from the prior art to regulate the torque generated by the electric machine and thus acting on the drive train to the desired drive torque. For this purpose, for example, in a control loop, an actual value of a control variable determining the torque of the electric machine (e.g., "motor current") can be regulated to a predetermined setpoint of this control variable, where the latter setpoint corresponds to the desired drive torque (target drive torque).

[0009] Especially at cold ambient temperatures, many common types of electric batteries used in the automotive sector (e.g., lithium-ion batteries) require special heating or cooling for efficiency and performance reasons, as well as to extend their lifespan.

[0010] 2. The battery needs to be preheated before it can be operated normally and thus, in particular, subjected to prolonged heavy loads, such as high discharge or charging currents. In the prior art, such preheating of the electric battery is achieved, for example, by means of an electrically operated heating device installed for this purpose. However, disadvantages of this solution include, besides the effort required to provide the electrical heating device, a relatively long preheating time and the associated energy consumption.

[0011] It is an object of the present invention to demonstrate a novel way in which the aforementioned problem, which occurs particularly at relatively low ambient temperatures, can be overcome when controlling an inverter of an electric machine in a drive train of a vehicle.

[0012] According to the present invention, this problem is solved in a method of the type mentioned at the outset by providing a special control mode in the case of a desired drive torque above a predetermined threshold torque and a temperature of the electric battery below a predetermined threshold temperature.

[0013] Advantageously, the invention enables, for example, the commissioning of a drive system even at cold ambient temperatures. The threshold temperature can be preset to suit the specific application. In many cases, a threshold temperature of at least -10°C, and in particular at least 0°C, is advantageous. Conversely, it is often advantageous if the threshold temperature is at most 30°C, and in particular at most 20°C.

[0014] According to the invention, in the aforementioned special control mode, a torque is generated by means of the electric machine which rapidly alternates between a torque above and below the desired drive torque, so that the desired drive torque is achieved on average over time. 202400509

[0015] 3

[0016] The invention is based on the idea of ​​utilizing the internal electrical resistance of the electric battery to heat it "from the inside" in a critical operating situation caused by an excessively low battery temperature. Particularly advantageously, a desired drive torque can also be generated in the drive train during this preheating process without damaging the battery. For this to work, it is essential that the torque generated by the electric motor rapidly alternates between a torque above and a torque below the desired drive torque, so that the desired drive torque is achieved on average over time.

[0017] In this control mode, the system alternates between the two drive torques (above and below the desired drive torque) at a time-related frequency, resulting (on average) in a potentially additional, predetermined target heat output. This time-related frequency preferably corresponds to a manipulated variable in a control system for the target heat output. The target heat output is generated by alternating between the drive torques, and in particular, primarily by the drive torque that exceeds the desired drive torque. The time-related frequency can correspond to a number of alternations between the two drive torques (above and below the desired drive torque), with the frequency referring to a time interval. The alternation can be regular, meaning the time intervals between successive alternations can be at least constant and can, if necessary, change with the target heat output.The change (between the drive torque above the desired drive torque and the drive torque below the desired drive torque) can also be irregular. The time-related frequency is, for example, at least 20, 50, 100, 200, or 1000 changes per second. The time-related frequency is, for example, at most 10,000, 500, 2,000, 1,000, or even at most 500, 200, or 100 changes per second. The time-related frequency is preferably designed such that the alternating torque thereby generated in the drive train is 202400509.

[0018] 4. The value is below a threshold that represents the limit at which the driving behavior or noise generated by the alternating torque becomes perceptible to the user of the vehicle in which the powertrain is installed. This depends not only on the user's sensitivity thresholds but also on the (acoustic and / or inertial) damping provided by the powertrain. The desired torque may result in an initial heat output in the battery, with a second heat output resulting from the alternating torque; the specified target heat output may correspond only to the second heat output, or the specified target heat output may correspond to a total target heat output generated in the battery, with the alternating torque representing the difference between the total heat output and the initial heat output.The adjustable parameters of the switching process used to generate the target heat output include, in particular, the frequency of the switching cycles over time, the magnitude of the drive torque exceeding the desired drive torque, and / or the magnitude of the drive torque falling below the desired drive torque, as well as, if applicable, the duration for which each of these conditions persists. At least one of these adjustable parameters is preferably a control variable of a temperature controller or temperature regulator whose control objective is a target heat output or target temperature, generated (among other things) by the switching process within the battery. The heat output is generated at the at least one internal resistance of an equivalent circuit of the battery. The battery is, in particular, a vehicle traction battery. Its nominal voltage is preferably at least 200 V, 400 V, 800 V, or more, but can also be 48 V.The term "rapidly" corresponds in particular to the time-related frequency mentioned here as an example, or is defined by this.

[0019] In one embodiment of the invention, in the aforementioned control mode, the torque above the desired drive torque is a positive torque and the torque below the desired drive torque is a negative torque.

[0020] The term "positive" moment here refers to a force generated by a "motor operation" of the electric machine, acting in the direction of the desired 202400509

[0021] 5

[0022] The driving torque is the torque acting against the direction of the desired driving torque, and the term "negative" torque accordingly refers to a torque generated by a "generator-like operation" of the electrical machine, acting in the opposite direction to the desired driving torque.

[0023] In this embodiment, the torque generated by the electric machine in the aforementioned (special) drive mode rapidly alternates between a positive torque (i.e., motor operation) and a negative torque (i.e., generator operation). This results not only in a rapid change in the battery current intensity but also in a rapid change in the direction of the battery current (between charging and discharging current). This change in current direction can be generally provided in the special control mode or dependent on one or more current operating parameters of the drive system (such as the currently desired drive torque and / or the current speed of the electric machine).

[0024] It has been found that in this specific control mode, a relatively high battery current (averaged in magnitude) can even be used, which, flowing through the battery's internal resistance, generates correspondingly large losses in order to heat the battery quickly and efficiently from the inside. At the same time, however, damage to the battery is prevented due to the rapid changes in current intensity and, if necessary, current direction (between charging and discharging current).

[0025] With the invention, a desired drive torque can advantageously be provided during the preheating process by means of the provided special control mode. This results as a time-averaged value of the time-dependent (rapidly changing) torque generated by the electric machine in this control mode. In practice, inertia in the drive train can advantageously contribute to a smoothing of the torque acting at the end of the drive train (e.g., vehicle wheels). 202400509

[0026] 6

[0027] In a further development of the invention, it is provided that, in the aforementioned control mode, the heat generated in the area of ​​the battery, the inverter, and / or the electric motor is used to heat a passenger compartment (e.g., the passenger cell) of the vehicle. Advantageously, this makes it possible to utilize the heat generated during operation in the aforementioned special control mode in the area of ​​the battery, the inverter, and / or the electric motor as a result of the losses there for heating a passenger compartment (e.g., the passenger cell) of the vehicle. Controlling and executing the corresponding transfer of heat from one or more of the aforementioned components to the passenger compartment can be achieved, for example, by a so-called thermal management system provided in the vehicle (e.g., comprising temperature sensors and heat exchangers, possibly with air conditioning fluid circulating in a loop, etc.).

[0028] In simple embodiments of the invention, the aforementioned "threshold torque" and / or "threshold temperature" are fixed, although setting a threshold torque of zero is also possible. In the latter case, the criterion to be verified during the execution of the method according to the invention for using the special control mode is reduced to the question of whether the battery temperature exceeds the threshold temperature or not. Therefore, any technical means for comparing the desired drive torque with such a threshold torque (of a fixed zero) become unnecessary, including means for "setting" this threshold torque. The special control mode is then always available if the temperature of the electric battery is below the specified threshold temperature.regardless of the desired drive torque (However, even in this case, it may be provided that at least one specific parameter of the rapid torque variation provided in the special control mode depends on the currently desired drive torque, as explained further below). 202400509.

[0029] 7

[0030] However, in contrast to a fixed specification, the invention may also provide for a variable specification of the "threshold torque" and / or the "threshold temperature", for example depending on certain instantaneous operating parameters that are determined on the relevant drive system of the vehicle.

[0031] If the currently desired drive torque does not exceed a predefined (and non-zero) threshold torque, a "normal control mode" can be used to generate a torque equal to the desired drive torque by means of the electric motor (i.e., without the rapid variation of the generated torque provided for in the special control mode). In the case of inverter control with regulation, the torque generated by the electric motor is then regulated to the desired drive torque (target drive torque). The criterion for providing the special control mode—namely, a desired drive torque exceeding the predefined threshold torque—takes into account the fact that, at low battery temperatures, a normal control mode can generally be used without problems for correspondingly small desired drive torques, i.e., without damaging the battery.Therefore, it is often advantageous to specify a non-zero threshold torque. However, the invention does not preclude specifying a zero threshold torque (either as a fixed setting or as a temporary setting under predetermined operating conditions). As explained above, however, with a "fixed zero threshold torque setting," no technical means for this setting are required, since the selection of the control mode (special control mode and normal control mode) then occurs independently of the desired drive torque (and depends solely on the battery temperature).

[0032] If the temperature of the electric battery is not below the specified threshold temperature, the normal control mode described above can also be used, in which the electrical 202400509

[0033] 8

[0034] The torque generated by the machine is equal to the desired drive torque (and there is no torque variation as provided for in the special control mode).

[0035] In one embodiment of the invention, the threshold torque is predetermined as a function of the temperature of the electric battery. This advantageously allows for even more demand-oriented control of the inverter or a demand-based switching between the aforementioned modes, normal control mode and special control mode. Alternatively or additionally, the threshold torque can be dependent on at least one further operating parameter of the drive system.

[0036] For this special control mode, it is essential that the torque generated by the electric machine rapidly alternates between a (positive) torque above the desired drive torque and a (e.g. negative) torque below the desired drive torque, so that the desired drive torque is achieved on average over time.

[0037] Regarding the specific design of this variation of the torque generated in the special control mode, the invention offers various possibilities or degrees of freedom in the form of "variation parameters." Such variation parameters include, for example, the variation frequency, the variation amplitude, and the variation's temporal profile, e.g., approximately rectangular or approximately sinusoidal, etc. Some possible configurations and thus advantageous optimization possibilities with respect to these parameters will be discussed below.

[0038] In one embodiment, the frequency of variation of the torque generated in the aforementioned control mode is in the range of 10 Hz to 1 kHz. At a very low frequency, the torque variation can be noticeable, for example, to vehicle occupants, whereas at too high a frequency, the battery current is more strongly filtered by a DC link capacitor typically installed in the inverter (and thus connected in parallel to the battery).

[0039] 9

[0040] (smoothed), thus reducing battery current variation and consequently also reducing the desired losses in the battery (heating). At very high frequencies, the torque variation might also no longer be precisely controllable, depending on the control concept used.

[0041] Considering these two aspects, the aforementioned frequency range has proven advantageous for most applications. The frequency of variation can be fixed or dependent on one or more specific operating parameters determined from the vehicle's drive system (e.g., battery temperature, electric motor speed, etc.).

[0042] In one embodiment, the time course of the variation is at least approximately rectangular. This allows, for example, a relatively high heating output to be achieved. In another embodiment, this time course is at least approximately sinusoidal. This can advantageously result, for example, in lower mechanical stress on the electric motor and the drive train.

[0043] Assuming that in practice there is an upper limit to the magnitude of both a positive torque (i.e., motor operation of the electric machine) and a negative torque (i.e., generator operation of the electric machine), certain limitations arise regarding the "desired drive torque" (target drive torque) achievable in the specific control mode. The latter is restricted to a range that depends, among other things, on the aforementioned upper limits. For example, the desired drive torque cannot be set so high as to correspond to one of the aforementioned upper limits. However, the limitation of the desired drive torque for the duration of a preheating process, typically a few minutes, is acceptable in practice. 202400509

[0044] 10

[0045] When a specific desired drive torque is set in the special control mode, there is generally also some leeway in terms of configuration, for example, regarding the amplitude of the variation of the torque generated by the electric machine. This amplitude, or rather the relevant torques, i.e., minima and maxima in the temporal profile (variation) of the generated torque, can, for example, be fixed within the scope of the invention. Alternatively, however, it is also possible to provide the values ​​of the aforementioned minima and / or maxima depending on one or more specific operating parameters determined for the drive system in question, such as, in particular, one or more of the following operating parameters: speed of the electric machine, desired drive torque, battery temperature.

[0046] In one embodiment, it is provided that, in varying the torque generated in the aforementioned control mode, the time periods with torque exceeding the desired drive torque and the time periods with torque below the desired drive torque are at least approximately equal in length. For example, it can be provided that each of these time periods occupies at least 30%, in particular at least 40%, of a cycle duration (e.g., cycle period). (Accordingly, each of these time periods then occupies at most 70%, in particular at most 60%, of the cycle duration.)

[0047] In one embodiment, it is provided that at least one parameter of the variation of the torque generated in the aforementioned control mode, i.e., e.g., the aforementioned frequency of the variation and / or e.g., the lengths of the aforementioned time intervals and / or e.g., an amplitude of the variation, is varied depending on one or more other operating parameters of the drive system. Such "other parameters" can, in particular, e.g., a rotational speed of the electric machine and / or the desired drive torque, or alternatively or additionally, e.g., the temperature of the battery. 202400509

[0048] 11

[0049] In a more specific embodiment of this design, it is provided, for example, that at least one parameter of the variation of the torque generated in the said control mode (in particular, for example, the values ​​of the minima and / or maxima of this torque, in relation to the desired drive torque) is varied as a function of a rotational speed of the electric machine.

[0050] In one embodiment of the method, it is provided that the method includes regulating the torque generated by the electric machine to a predetermined setpoint. This regulation can be implemented in both special control mode and normal control mode. Since conventional control methods and devices of the type of interest here often already provide for regulating the torque generated by the electric machine and thus acting on the drive train to a corresponding setpoint (desired torque), the invention can be implemented in this case without great effort, for example, by adjusting the torque based on the battery temperature (and possibly the battery temperature).Depending on the desired drive torque, a special control mode and a normal control mode are selected. In the special control mode, a setpoint is specified that rapidly alternates between a first (positive) setpoint corresponding to a torque above the desired drive torque and a second (positive or negative) setpoint corresponding to a torque below the desired drive torque. In contrast, in the normal control mode, a setpoint corresponding to the desired drive torque can be specified.

[0051] According to a further aspect of the present invention, the problem stated at the outset is solved in a device of the type mentioned at the outset by the fact that it is designed to provide a (special) control mode in the case of a desired drive torque above a predetermined threshold torque and a temperature of the electric battery below a predetermined threshold temperature, in which a torque is generated by means of the electric machine which rapidly alternates between a torque above the desired drive torque and a temperature below a predetermined threshold temperature.

[0052] 12

[0053] The desired drive torque is determined by a specific torque and a torque that is below the desired drive torque, so that the desired drive torque is achieved on average over time.

[0054] The embodiments and special configurations described here for the method according to the invention can, individually or in any combination, also be provided in an analogous manner as embodiments or special configurations of the device according to the invention, and vice versa.

[0055] According to a further aspect of the present invention, a computer program product comprising program code is proposed which, executed on a data processing device, e.g. a drive control device provided in a vehicle, performs a method of the type described herein.

[0056] The invention is further described below with reference to exemplary embodiments and the accompanying drawings. These schematically depict:

[0057] Fig. 1 shows a block diagram of a vehicle drive train with an electric machine and other components of a drive system according to an exemplary embodiment.

[0058] Fig. 2 shows a circuit diagram of an inverter with an electrical machine connected to it according to an exemplary embodiment.

[0059] Fig. 3 shows a block diagram of a control device according to an exemplary embodiment.

[0060] Fig. 4 is a diagram illustrating the time course of the torque generated by an electric machine, and

[0061] Fig. 5 is a diagram illustrating the dependence of a threshold moment on battery temperature. 202400509

[0062] 13

[0063] Fig. 1 shows an embodiment of a drive train 4 of a vehicle and other components of a drive system of the vehicle.

[0064] The drive train 4 shown in Fig. 1 comprises an electric machine (electric motor) 3, a shaft driven by it, and further along the drive train 4, for example, a gearbox 5 and a differential gearbox 6, as shown.

[0065] In the illustrated embodiment, the vehicle is an electric vehicle, e.g., a battery electric vehicle (BEV), which can be driven by the electric machine 3 via the illustrated drivetrain 4, wherein the transmission 5 serves as a reduction gear and the differential 6 distributes the torque to two wheels 7 of a drive axle of the vehicle. The gear ratio of the transmission 5, i.e., the ratio between the input speed of the shaft and the output speed of a shaft leading to the differential, can be, for example, in the range of approximately 20:1 to 5:1. In contrast to the illustration in Fig. 1, the transmission 5 could also be, for example, structurally integrated with the electric machine 3.

[0066] During operation of the drive system, the electric machine 3 provides a "desired torque" Tqprop to the drive train 4.

[0067] The drive system shown in Fig. 1 further comprises an inverter 2 for generating a motor current for the electric machine 3, in the example a three-phase AC current with three components (phase currents) 1u, 1v, 1w.

[0068] For the electrical supply of the inverter 2, the drive system also includes an electric battery 1, whose battery voltage provides a supply voltage (DC voltage) with potentials DC+ and DC- for the inverter 2.

[0069] The drive system also includes a control device 10, by means of which the electric machine 3 is controlled via the inverter 2. 202400509

[0070] 14

[0071] In the example shown, the control device 10 is implemented by a software-controlled computing device located on board the vehicle, such as a (or several communicatively connected) microcontroller or another digital signal processing device.

[0072] The device 10 can, for example, be in communication with a vehicle control unit (not shown) to receive a target value Cprop via this communication link, e.g., an interface of a digital data bus system. This target value is representative of the aforementioned "desired drive torque" Tqprop. The vehicle control unit can specify this target value Cprop, for example, essentially based on the operating actions currently communicated to the vehicle control unit from a vehicle control unit. This could be, for example, dependent on the position of an accelerator pedal operated by the driver and the position of a control unit operated by the driver to determine the vehicle's direction of travel. A torque requested by the driver in this way (e.g., corresponding to the position of an accelerator pedal) does not necessarily have to be passed on to the control device 10 as the target value Cprop in a 1:1 manner.Rather, the vehicle control unit can, for example, within the framework of comfort and safety functionalities, also pass this requirement on to the control device 10 in a modified form.

[0073] Based on this setpoint Cprop, the control device 10 generates a control signal for the inverter 2, which in the illustrated example is formed by three control signal components Cu, Cv, Cw, each of which serves to control one of the three phase currents lu, Iv, Iw. In a manner known per se, the components Cu, Cv, Cw can, for example, be PWM control signals, which serve to generate sinusoidal waveforms of the phase currents lu, Iv, Iw supplied by the inverter 2, each waveform being phase-shifted by 120° relative to the others. 202400509

[0074] 15

[0075] Through appropriate control, e.g. by a (not shown) vehicle control unit, the system formed from the electric battery 1, the inverter 2 and the electric machine 3 can realize both a "motor operation" of the electric machine 3, in which energy is transferred from the battery 1 to the electric machine 3 via the inverter 2, and a "generative operation" of the electric machine 3, in which energy is transferred from the electric machine 3 to the battery 1 via the inverter 2 (recuperation operation of the vehicle).

[0076] Fig. 2 shows a circuit diagram of the inverter 2 used in the drive system of Fig. 1 with the electric machine 3 connected to it. In the illustrated example, the inverter 2 comprises, in a manner known per se, a parallel arrangement of three half-bridge circuits connected to a common supply voltage (corresponding to the battery voltage with the potentials DC+ and DC-).

[0077] Each of the half-bridge circuits of inverter 2 is formed by a series connection of two controllable switches (here: MOSFETs), whereby a phase voltage is provided at a center tap of the respective series connection. This voltage is applied to the electrical machine 3 via one of three phase lines U, V, W to supply the phase currents Iu, Iv, Iw. The two switches of each half-bridge circuit are controlled in a manner known per se by the corresponding complementary control signal components Cu, Cv, Cw.

[0078] The electrical machine 3 (here: three-phase AC machine) in the example comprises a stator winding arrangement 31 connected to the phase line arrangement U, V, W with three stator windings connected in a so-called star arrangement as shown.

[0079] Fig. 3 shows a block diagram of the control device 10 used in the drive system of Fig. 1 according to an exemplary embodiment. In the case of a 202400509

[0080] 16

[0081] The implementation of the control device 10 as a software-controlled computing device means that the components of the control device 10 shown in Fig. 3 are realized or understood as components or functionalities of the corresponding software (control program).

[0082] The control device 10 has a control loop to regulate actual values ​​Iqact, Idact of control variables Iq, Id, which determine a rotary drive of the electric machine 3 according to a field-oriented vector control, to corresponding setpoint values ​​Iqsp, Idsp of these control variables Iq, Id. Here, "Id" can, for example, denote a current component generating the magnetizing current and "Iq" can, for example, denote a current component generating the torque.

[0083] The actual values ​​Iqact, Idact are calculated by the control device 10 based on the values ​​of the phase currents lu, Iv, Iw detected at the electrical machine 3 (Clarke-Parks transformation).

[0084] The setpoint values ​​Iqsp and Idsp are generated and output by a control unit 11, based on the received setpoint Cprop, which in turn was determined, for example, by a (not shown) vehicle control unit taking into account the vehicle's accelerator pedal position, and also considering the temperature Tbat of the electric battery 1. Additional information supplied to the control unit 11 can also be considered when setting the values ​​Iqsp and Idsp.

[0085] In the control device 10 of Fig. 3, a control loop is formed by:

[0086] - a first transformation device 15 for the Clarke-Parks transformation of the phase currents lu, lv, lw measured at the electric machine 3 into the corresponding actual values ​​Iqact, Idact of the control variables Iq, Id taking into account the rotation signal Srot,

[0087] - a comparison device (subtraction node) for comparing the actual values ​​Iqact, Idact with the corresponding target values ​​Iqsp, Idsp, 202400509

[0088] 17

[0089] - a controller (here: PI controller) 12 for generating control signals Idctl, Iqctl based on the result of comparing the actual values ​​Iqact, Idact with the setpoint values ​​Iqsp, Idsp,

[0090] - a second transformation device 13 for the inverse Clarke transformation of the control signals Idctl, Iqctl into control signals a, ß in a stationary (stator-fixed) coordinate system according to the vector control, taking into account the rotation signal Srot,

[0091] - a modulation device 14 for space vector modulation ("space vector PWM") based on the control signals a, ß for generating PWM phase current control signals Cu, Cv, Cw for controlling the inverter 2 for generating the phase voltages and thus the resulting phase currents lu, Iv, Iw.

[0092] By means of a rotational position sensor 20 (e.g. rotary encoder or "resolver") arranged in the example on the electric machine 3, a rotational position is determined for a rotary angular position. <p der elektrischen Maschine 3 repräsentatives Rotationssignal "Srot" gewonnen. Das Rotationssignal Srot liefert eine zeitaufgelöste Information über die Drehstellung eines Rotors der elektrischen Maschine 3. Diese Information wird im dargestellten Beispiel der sog. Vektorregelung zur Durchführung der vorgenannten mathematischen Transformationen (in den Einrichtungen 13 und 15) genutzt.

[0093] In the control loop 12, 13, 14, 15, the actual values ​​Iqact, Idact from the control variables Iq, Id determining the rotary drive of the electric machine 3 are controlled by the corresponding setpoint values ​​Iqsp, Idsp of the respective control variable Iq, Id supplied to the control device 10.

[0094] Returning to Fig. 1, the control unit 10, in conjunction with the inverter 2, implements the received input Cprop, resulting in the desired drive torque Tqprop in the drive train 4. 202400509

[0095] 18

[0096] Especially in cold ambient temperatures, it may be necessary (depending on the temperature of battery 1) to preheat battery 1 before it can be operated normally.

[0097] With regard to this problem, the control device 10 is designed to provide a "special control mode" in the case of a desired drive torque Tqprop (see thick line in Fig. 4) that is above a predetermined threshold torque (such as Tqth in Fig. 5) and a temperature of the electric battery 1 that is below a predetermined threshold temperature (such as Tbatth in Fig. 5), which is explained in more detail below with reference to Figs. 4 and 5.

[0098] To enable the control unit 10 to determine whether the temperature of the electric battery 1 is below the predetermined threshold temperature, the battery 1 in this example is equipped with appropriate sensors, including at least one temperature sensor arranged within the battery 1. As symbolized in Fig. 1, information about the battery temperature Tbat determined by the sensors is communicated to the control unit 10 (e.g., via a digital data bus system). Electric batteries of the type of interest here are generally equipped with a so-called battery management system (BMS) for controlling and monitoring battery operation, so that, for example, a battery temperature Tbat determined by a BMS can be advantageously used to implement the invention.

[0099] Fig. 4 shows an example of the course of a torque Tq (thin line in Fig. 4) generated by the electric machine 3 in the aforementioned "special control mode" as a function of time t.

[0100] A special feature of the temporal profile of the torque Tq generated by the electric machine 3 is that it rapidly alternates between a value above the desired drive torque Tqprop 202400509

[0101] 19

[0102] The torque Tq+ and a torque Tq- below the desired drive torque Tqprop result in the desired drive torque Tqprop on average over time (thick line in Fig. 4). The exact values ​​of Tq+ and Tq- are determined according to a control algorithm running in the control device 10, e.g., depending on certain operating parameters (such as the currently desired drive torque Tqprop, the current speed of the electric machine 3, and / or the current battery temperature Tbat).

[0103] In the illustrated example (Fig. 4), the torque Tq+ is positive (motor operation) and the torque Tq- is negative (generator operation). However, within the scope of the invention, this is only one possible embodiment of the torque variation (the essential point is that the desired drive torque Tqprop is achieved on average over time). Alternatively, the torque Tq- could also be positive (but below Tqprop), either generally or, for example, depending on certain operating parameters such as the currently desired drive torque Tqprop and / or the current rotational speed of the electric machine 3.

[0104] For the sake of better recognizability, the frequency of variation of the moment Tq, i.e., the rapid back-and-forth switching between the moments Tq+ and Tq-, is lower in the representation of Fig. 4 than is practical.

[0105] Preferably, this frequency is at least 5 Hz, and in particular at least 10 Hz, within the scope of the invention. On the other hand, it is usually advantageous if this frequency is a maximum of 2 kHz, and in particular a maximum of 1 kHz. In one embodiment, the frequency is less than 1 kHz, and in particular less than 500 Hz.

[0106] In the example shown in Fig. 4, a fixed value is specified for Tq-, and the value Tq+ is varied depending on the desired drive torque Tqprop (equivalent to setpoint Cprop) such that the desired drive torque Tqprop is achieved on average over time. In contrast, within the scope of the invention, the values ​​of Tq+ and / or Tq- can be varied relative to the value of 202400509.

[0107] 20

[0108] Tqprop can also be advantageously optimized by determining Tq+ and / or Tq- in a different way, for example, depending on other operating parameters of the drive system (e.g., battery temperature Tbat and / or, for example, the speed of the electric machine 3, etc.). In particular, it could then also turn out, for example, within the framework of such a dependency, that a non-negative value for Tq- is specified in certain operating situations.

[0109] In the example shown in Fig. 4, it is assumed that the drive system in question was put into operation at time t=0 and that the control device 10 detected that the temperature Tbat of the electric battery 1 was below a predetermined threshold temperature (see Tbatth in Fig. 5). More generally, this threshold temperature can be predefined, for example, by the control device 10. Alternatively, it is possible, for example, to specify the value of the threshold temperature to be used to the control device 10 externally (e.g., by a vehicle control unit). The latter can be implemented, for example, in the embodiment shown in Fig. 3, as an additional data input alongside the inputs Cprop and Tbat.

[0110] From a point in time approximately at t = 1 s, a gradually increasing desired drive torque Tqprop is required (due to the corresponding specification Cprop). As long as the desired drive torque Tqprop remains below the specified threshold torque, approximately 5 Nm in the example of Fig. 4, a "normal control mode" is provided, in which the torque Tq generated by the electric machine 3 is regulated to the desired drive torque Tqprop (target drive torque). This takes into account the fact that even at a low battery temperature Tbat, the generation of the relatively small desired drive torque Tqprop (here: up to 5 Nm) does not damage the battery 1.

[0111] From a point in time at approximately t=4s, the desired drive torque Tqprop exceeds the specified threshold torque (here: 5 Nm) (due to the corresponding setting Cprop), and the control switches to the "special control mode" in which the electric machine 3 202400509

[0112] 21 The generated torque Tq is rapidly switched back and forth between the aforementioned torques Tq+ and Tq-, whereby the torque Tq+ is provided by a motor operation and the torque Tq- by a generator operation of the electric machine 3 such that the desired drive torque Tqprop is obtained on the drive train 4 in a time average (thick line in Fig. 4).

[0113] Advantageously, vehicle propulsion can begin in normal control mode at an early stage (from approximately t=1 s) and then continue in the special control mode (from approximately t=4 s) even at higher desired drive torque Tqprop, in which effective heating of the battery 1 also takes place. Within the scope of the invention, the special control mode can therefore also be referred to as the "preheating control mode".

[0114] During the further course of operation of the drive system, the battery temperature Tbat will rise and eventually, typically a few minutes after the start of operation, exceed the predetermined threshold temperature. From then on, the control mode provided by the control device 10 according to the control algorithm running within it switches back to the normal control mode. This is also illustrated in the example of Fig. 4 by a later course of the generated torque Tq from about t=600s. Here, there is no rapid variation of the generated torque Tq (between predetermined values ​​Tq+, Tq-), but rather the generated torque Tq is again regulated to the drive torque Tqprop desired according to the specification Cprop.

[0115] Fig. 5 shows an exemplary diagram of an optional dependency of the "threshold torque" Tqth on the battery temperature Tbat, as provided for in the invention. In this example, it is assumed that a threshold temperature of Tbatth = +25°C is specified.

[0116] In the example shown, a threshold torque Tqth=0 is specified for very low battery temperatures Tbat down to approximately Tbat=-25°C. When the drive system is operated in this situation, the inverter is controlled according to 202400509.

[0117] 22 of the special control mode in every case, i.e. even with a very small predetermined desired drive torque Tqprop, with variation of the generated torque Tq (back and forth between predetermined values ​​Tq+, Tq-).

[0118] In the following temperature range up to Tbat = Tbatth = +25°C, the threshold torque Tqth increases to a maximum value of Tqth = Tqmax. In the example shown in Fig. 5, this increase is linear. When the drive system is operated in this temperature range, the inverter is controlled either in a special control mode (for Tqprop > Tqth) or in normal mode (for Tqprop <= Tqth), i.e., the appropriate control mode is selected depending on the value of the specified desired drive torque Tqprop.

[0119] In the subsequent higher temperature range from Tbat=+25°C, no value for the threshold torque Tqth needs to be specified, since in the example the threshold temperature Tbattth is then exceeded and control takes place in "normal control mode" (see right side of Fig. 4).

[0120] In contrast to the examples described with reference to Figures 4 and 5, where a threshold torque Tqth is specified within the control method and used in the algorithm of this method, a threshold torque Tqth fixed at "zero" from the outset could also be provided. In this case, a specification (of Tqth) is unnecessary in the method according to the invention, and the special control mode always occurs when the battery temperature Tbat is below the specified threshold temperature Tbatth (i.e., regardless of the desired drive torque Tqprop). In the scenario according to Figure 4, the torque variation (rapid switching between Tq+ and Tq-) would then occur from approximately t=1 s (as soon as a drive torque Tqprop > 0 is desired). 202400509

[0121] 23

[0122] Reference symbol list

[0123] 1 electric battery 2 inverter 3 electric machine 4 drive train 5 reduction gear 6 differential gear 7 vehicle wheels 10 control device 11 preset device 12 controller 13 second transformation device 14 modulation device 15 first transformation device 20 rotation position sensor 31 stator winding arrangement P rotation angle position Srot rotation signal DC+, DC- battery voltage potentials U, V, W phase lines Cu, Cv, Cw control signal components (PWM signals) Uu, Uv, Uw phase voltages l1, Iv, Iw phase currents Iq, Id control variables Iqact, Idact actual values ​​(of the control variables) Iqsp, Idsp setpoint values ​​(of the control variables) Idctl, Iqctl control signals a, ß control signals Cprop preset (for desired drive torque) Tqprop desired drive torque (in the drive train) Tq torque (generated by electric machine) Tqth threshold torque Tbat Battery temperature Tbatth Threshold temperature t Time

Claims

202400509 24 Patent claims 1. Method for controlling an inverter (2) between an electric battery (1) and an electric machine (3) arranged in a drive train (4) of a vehicle, in order to produce a desired drive torque (Tqprop) in the drive train (4) by means of the electric machine (3), characterized in that, in the case of a desired drive torque (Tqprop) above a predetermined threshold torque (Tqth) and a temperature (Tbat) of the electric battery (1) below a predetermined threshold temperature (Tbatth), a control mode is provided in which a torque (Tq) is generated by means of the electric machine (3) which rapidly alternates between a torque (Tq+) above the desired drive torque (Tqprop) and a torque (Tq-) below the desired drive torque (Tqprop), so that the desired drive torque (Tqprop) is obtained on average over time.

2. Method according to claim 1, wherein in the said control mode the torque (Tq+) above the desired drive torque (Tqprop) is a positive torque and the torque (Tq-) below the desired drive torque (Tqprop) is a negative torque.

3. Method according to claim 1 or 2, wherein the threshold moment (Tqth) is predetermined as a function of the temperature (Tbat) of the electric battery (1 ).

4. Method according to one of the preceding claims, wherein the frequency of the variation of the moment (Tq) generated in the said control mode is in the range of 10 Hz to 1 kHz.

5. Method according to one of the preceding claims, wherein in the variation of the torque (Tq) generated in the said control mode the time periods with torque (Tq+) exceeding the desired drive torque (Tqprop) and the 202400509 25 Time periods with torque (Tq-) below the desired drive torque (Tqprop) are at least approximately the same length.

6. Method according to one of the preceding claims, wherein at least one parameter of the variation of the torque (Tq) generated in the said control mode is varied as a function of a rotational speed of the electric machine (3).

7. Method according to one of the preceding claims, comprising a control of the generated torque (Tq) to a predetermined setpoint value.

8. Method according to one of the preceding claims, wherein in the said control mode, heat generated in the area of ​​the battery (1), the inverter (2) and / or the electric machine (3) is used for heating a passenger cell of the vehicle.

9. Device (10) for controlling an inverter (2) between an electric battery (1) and an electric machine (3) arranged in a drive train (4) of a vehicle, in order to generate a desired drive torque (Tqprop) in the drive train (4) by means of the electric machine (3), characterized in that the device is configured to provide a control mode in the case of a desired drive torque (Tqprop) above a predetermined threshold torque (Tqth) and a temperature (Tbat) of the electric battery (1) below a predetermined threshold temperature (Tbatth), in which a torque (Tq) is generated by means of the electric machine (3) which rapidly alternates between a torque (Tq+) above the desired drive torque (Tqprop) and a torque (Tq-) below the desired drive torque (Tqprop).so that the desired drive torque (Tqprop) is achieved on average over time.

10. Device (10) according to claim 9, wherein in the said control mode the torque (Tq+) exceeding the desired drive torque (Tqprop) is a 202400509 26 positive moment and the moment (Tq-) below the desired drive torque (Tqprop) is a negative moment.

11. Computer program product comprising program code which, when executed on a data processing device, e.g. a drive control device (10) provided in a vehicle, performs a method according to one of claims 1 to 8.

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