System for targeted loss generation in an electric motor over the entire operating range of the electric motor, electric motor, motor vehicle drive and method for operating an electromotive motor vehicle drive

Abstract

The invention relates to a system (1) for controlling the operation of an electric motor which is provided for driving a motor vehicle, said system having a field weakening controller (2) which accesses the stator flux during operation in a controlling manner in order to achieve a field weakening, wherein a loss controller (3) is provided, which is prepared to perform controlling of the power loss from a target loss and an actual loss of power, wherein the loss controller (3) is configured such that the stator flux is used as a manipulated variable. The invention also relates to a synchronous machine having such a system (1), and to a motor vehicle drive having such a synchronous machine. Furthermore, the invention relates to a method for operating an electromotive motor vehicle drive, wherein the system (1) according to the invention is included and is operated in a targeted manner such that a target power loss is achieved.

Description

[0001] P241063

[0002] - 1 -

[0003] System for targeted loss generation in an electric motor across the entire operating range of the electric motor, electric motor, motor vehicle drive and method for operating an electric motor vehicle drive

[0004] The invention relates to a system for controlling the operation of an electric motor intended for driving a motor vehicle, with a field weakening controller which, during operation, accesses the stator flux in a controlling manner in order to achieve field weakening, wherein a loss controller is provided which is prepared to control the power loss from a target loss and an actual loss of power.

[0005] Numerous documents are already known from the prior art, such as US 2018 / 0083509 A1, WO 2017 / 214234 A1, EP 2 540 552 B1, the

[0006] US 10183580 B2 and DE 102019 133 634 A1. While previously the only conceivable option was to avoid losses during the operation of electric motors, current technology offers numerous considerations for eliminating electric motor-independent heating systems in motor vehicles. For some time now, the fundamental idea has been to operate electric motors not at their optimal efficiency, but with controlled losses, in order to utilize these losses and the associated heat for heating vehicle interiors or batteries.

[0007] However, all known control strategies and systems are incomplete and require improvement. The invention aims to address this by intervening in an improvement manner and eliminating or at least mitigating the disadvantages known from the prior art.

[0008] In a generic system, this is achieved according to the invention by setting up the loss controller in such a way that the stator flux is used as the manipulated variable by the loss controller.

[0009] In this way, the dynamics and robustness of the control system are not limited, and existing disadvantages are eliminated. P241063

[0010] - 2 -

[0011] The invention thus presents a method for controlling additional losses in electric motors using field-oriented control across the entire operating range of the electric motor, while maintaining the required torque. In other words, the inventive solution consists of shifting the operating point for generating additional losses depending on the stator flux, thereby also allowing or shifting to dq current pairs that have a smaller d-current than the point on an MTPV line. An MTPV line is understood to be a "Max Torque Per Volt" line.

[0012] This operating range is not currently reached during efficiency-optimized operation of an electric motor. When calculating losses, the limiting flux value of the field weakening controller is always taken into account to ensure correct field weakening. A method as disclosed in DE 102023 101 155 A1, which is considered integrated here, is used as the basis for determining the target current. That earlier patent application presents a vector control method for a synchronous machine and a control unit. Specifically, it presents a vector control method for a synchronous machine, particularly a permanent magnet synchronous machine, in which the q-axis and d-axis target currents (lq, Id) are determined by respective assignments that define a target torque (MTgt) and a target flux (M^Tgt-MTPA) with the q-axis target current (lq) and d-axis target current (Id), respectively.The d-axis target current (Id) is determined without considering a voltage variation of a voltage to be applied to the stator windings of the synchronous machine, whereby the voltage variation is previously controlled or compensated by adjusting the target flux strength.

[0013] The details disclosed in that earlier patent application are also to be considered as included in this invention now presented. P241063

[0014] - 3 -

[0015] This earlier patent application is now improved by the present invention in such a way that the method already known from that earlier patent application is extended to include the targeted generation of losses in all areas of operation.

[0016] The inventive solution to the problem can therefore be seen in the fact that the control method operates on the basis of field-oriented control. The combination of d-current and q-current for the selected torque is shifted along the torque hyperbola compared to the efficiency-optimal operation or the point with minimum stator current, such that (intentionally) increased losses occur.

[0017] This shift leads to a smaller d-current (more negative) and an adjusted q-current. To determine this shift, taking all boundary conditions for dynamic robust control into account, the stator flux is used as the key parameter. This is because the stator flux is used in the overall electric motor control strategy to determine the field weakening. To avoid compromising the advantageous field weakening based on the stator flux, the loss generation strategy also relies on the stator flux and interacts with the field weakening strategy.

[0018] The intended behavior is that the flux determined by the flux weakening controller (MJ-TgtMTPA; also referred to as Psi_TgtFluxWeakeningController or Psi-TgtFieldWeakeningController) is modified by the loss controller and then passed on to the setpoint current tables. Additionally, a range 1 or 2 for the setpoint flux is determined and passed on to the setpoint current tables. The loss controller has a flux overflow signal which becomes non-zero as soon as the loss controller encounters a manifold limit. This overflow, in turn, limits the flux weakening controller. The loss controller also requires the setpoint power loss, the actual power loss (which can be estimated or measured), the setpoint torque, and optionally the magnet temperature (or rotor temperature) for a separately excited synchronous machine. P241063

[0019] - 4 -

[0020] The division of the target current characteristic into two regions, 1 and 2, is necessary because a desired torque and stator flux each have two possible dq current pairs. The boundary between the two regions is the MTPV line, or analogously, the "Max Torque Per Flux" (MTPF) line. Region 1 here denotes dq current pairs where the d-current is greater than the d-current on the MTPF line. Region 2 denotes dq current pairs where the d-current is less than the d-current on the MTPF line.

[0021] The loss controller takes as its input the difference between the target loss and the actual loss, and as its output the flux. It can preferably be implemented as a PI controller.

[0022] The controller output, flux, must be switched between range 1 and range 2. In range 1, the flux must be reduced to increase losses. Once the flux is reduced to the MTPF line, the controller switches to range 2 and increases the flux again. For this switching to function correctly, the MTPF line must be defined as a function of the torque (and optionally the rotor temperature). The losses increase significantly due to the increased ohmic losses, because shifting the target current point towards lower d-currents increases the current magnitude.

[0023] The loss controller has several limits to consider:

[0024] 1) It does not increase the flow beyond what is specified by the flow weakening regulator, so that field weakening is always guaranteed.

[0025] 2) It must achieve the desired torque without exceeding the current limit. For this purpose, a characteristic curve must be defined that outputs the flux at the current limit as a function of the torque and whether this value lies in range 1 or 2. If the flux value at the current limit is in range 1, the flux in range 1 may only be reduced to the extent that a switch to range 2 is prevented. If the flux value at the current limit is in range 2, the flux in range 2 may only be increased up to this flux value.

[0026] As soon as the flux value of the flux attenuator is modified (reduced) by the loss controller, the flux attenuator is limited (overflow signal) so that P241063

[0027] - 5 - this cannot regulate towards larger fluxes. This occurs because, as soon as the loss controller regulates for additional losses, the required voltage of the current controller decreases, since the output of the flux attenuator has been modified. The flux attenuator must continue to regulate towards smaller fluxes, as proper flux attenuation must always be ensured.

[0028] The target current tables store the dq current pairs as a function of torque (or optionally as relative torque to the maximum torque), flux, optionally rotor temperature and range.

[0029] Advantageous embodiments are claimed in the dependent claims and are explained in more detail below.

[0030] It is therefore advantageous if the loss controller has a converter that is configured to determine an associated d-current and q-current depending on at least the parameters target torque, target stator flux and range information (range 1 or range 2), wherein the range information refers to whether the d-current of a dq-current point is greater (range 1) or less (range 2) than the d-current of the dq-current point at the respective given torque on the MTPV line, wherein the loss controller, which can also be referred to as a power loss controller, is configured to specifically select the smaller d-current of range 2.

[0031] It has also proven advantageous to have a current table stored with the converter. This allows for simple conversion.

[0032] An advantageous embodiment is further characterized in that the loss controller is designed to consider a rotor temperature as an input value when calculating the MTPV line and / or the converter uses the rotor temperature during conversion. Using the rotor temperature increases accuracy. P241063

[0033] - 6 -

[0034] It is advantageous if the loss controller is prepared to always consider the stator flux specification of the field weakening controller as a limit, so that only dq current pairs are required that can be achieved with the available DC voltage.

[0035] It is advantageous if the loss controller is prepared to limit the manipulated variable "stator flux" so that the associated dq current pair does not exceed a permissible phase current of the stator.

[0036] If the loss controller is prepared to deliberately generate a torque that corresponds to a target torque, then a desired behavior of the electric motor can be achieved.

[0037] The invention also relates to a synchronous machine for a drive of a motor vehicle with a system according to the invention.

[0038] The invention also relates to a motor vehicle drive with a synchronous machine of this design.

[0039] Ultimately, the invention also relates to a method for operating an electric motor vehicle drive, wherein the system according to the invention is included and is operated in such a targeted manner that a target power loss occurs or is achieved.

[0040] The invention is explained in more detail below with the aid of a drawing. The drawing shows:

[0041] Fig. 1 shows a section of a first schematically illustrated embodiment of a system according to the invention and

[0042] Fig. 2 shows a schematically sketched sequence of a control system according to the invention in a dq flow diagram.

[0043] The figures are schematic and serve only to illustrate the invention. The same elements are identified by the same reference numerals. P241063

[0044] - 7 -

[0045] Figure 1 shows a system 1 according to the invention for controlling an electric motor (not shown). The input Uctri_req could also be called Uctrl_req. The system 1 has a field weakening controller 2 and a loss controller 3. Furthermore, a converter 4 is provided. The converter 4 is designed as a current table or uses current tables. There is a section for determining the efficiency-optimal flux. This section is designated with reference numeral 5. In addition, there is a voltage control section 6. The converter includes a normalization section 7. There is also a maximum torque determination section 8. In the present embodiment, a current table 9 is also included. The rotor temperature is denoted Tpotor. The target torque is denoted MTgt. A voltage currently applied to the stator winding is denoted Uctri_req. Umax denotes the maximum voltage. The current electrical frequency is denoted CÜEI.The target flux strength of the flux attenuation controller is denoted by i Tgt_MTPA. The flux strength for the lowest stator current is denoted as M- X-MTPA. The target torque is denoted by MTgt, as already explained. The normalized target torque is denoted as Mreiativ. The maximum torque is Mmax_MTPA.

[0046] Target values ​​are referenced with "Tgt" and rotor-related values ​​with "Rtr".

[0047] In Fig. 2, Id is plotted on the abscissa and l on the ordinate. qThe abscissa is referenced by reference numeral 10 and the ordinate by reference numeral 11. The current limit is referenced by reference numeral 12. It should be noted that the current limit is actually circular; ideally, a quarter circle would be drawn. An iso-torque hyperbola is shown by reference numeral 13. An MTPL line is referenced by reference numeral 14 and an MTPV line by reference numeral 15. A region 2 is shown hatched from bottom left to top right between the current limit 12, the abscissa 10, and the MTPV line 15. A region 17, hatched from top left to bottom right, exists between the current limit 12, the ordinate 11, the abscissa 10, and the MTPV line. A control according to the invention follows the one indicated by arrow 18. P241063

[0048] - 8 - designated path, for example. An iso-stator flux ellipse is indicated by reference symbol 19.

[0049] The control process can be implemented in a PI controller.

[0050] P241063

[0051] - 9 -

[0052] List of reference signs

[0053] 1 system

[0054] 2 field weakening regulators

[0055] 3 loss controllers

[0056] 4 converters

[0057] Section 5 on determining the efficiency-optimal flow rate

[0058] 6 Voltage regulation section

[0059] 7 Standardization section

[0060] 8 Maximum Moment Determination Section

[0061] 9 Current table

[0062] 10 ID

[0063] 11 lq

[0064] 12 Current limit

[0065] 13 Iso-torque hyperbola

[0066] 14 MTPL line

[0067] 15 MTPV line

[0068] 16 Area 2

[0069] 17 Area 1

[0070] 18 Regulatory path

[0071] 19 Iso-Statorfluss-Ellipse

Claims

P241063 - 10 - Patent claims 1. System (1) for controlling the operation of an electric motor intended for driving a motor vehicle, comprising a field weakening controller (2) which, during operation, controls the stator flux to achieve field weakening, wherein a loss controller (3) is provided which is prepared to control the power loss from a target loss and an actual loss of power, characterized in that the loss controller (3) is configured such that the stator flux is used as the manipulated variable.

2. System (1) according to claim 1, characterized in that the loss controller (3) has a converter (4) which is configured to determine an associated d-current and q-current depending on at least the parameters target torque, target stator flux and a range information (range 1 and then range 2), wherein the range information (range 1 or range 2) relates to whether the d-current of a dq current point is greater (range 1) or less (range 2) than the d-current of the dq current point at the respective torque present on the MTPV line, wherein the loss controller (3) is configured to selectively choose the smaller d-current of range 2 (16).

3. System (1 ) according to claim 1 , characterized in that a current table (9) is stored in the converter (4).

4. System (1 ) according to one of claims 1 to 3, characterized in that the loss controller (3) is designed to take into account a rotor temperature as an input value when calculating the MTPV line and / or the converter (4) uses the rotor temperature during conversion.

5. System (1 ) according to one of claims 1 to 4, characterized in that the loss controller (3) is prepared to always take into account the stator flux specification of the field weakening controller (2) as a limit, so that only dq current pairs are required which can be achieved with the available DC voltage. P241063 - 11 - 6. System (1 ) according to one of claims 1 to 5, characterized in that the loss controller (3) is prepared to limit the manipulated variable stator flux so that the associated dq current pair does not exceed a permissible phase current of the stator.

7. System (1 ) according to one of claims 1 to 6, characterized in that the loss controller (3) is prepared to selectively cause a torque corresponding to a target torque.

8. Synchronous machine for a drive of a motor vehicle with a system (1 ) according to one of the preceding claims.

9. Motor vehicle drive with a synchronous machine according to claim 8.

10. Method for operating an electric motor vehicle drive, wherein the system (1) according to one of claims 1 to 7 is included, which is operated in such a targeted manner as to achieve a target power loss.

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