Control system for an electric machine for generating a braking torque by means of the electric machine and method for operating a control system for an electric machine

Abstract

The invention provides a control system (10) for an electric machine (EM) for generating a braking torque at a traction drive by means of the electric machine (EM), the control system comprising a control device (SE), wherein the control device (SE) is configured to: determine the torque (BM) of the electric machine (EM) and thereafter determine the generator current (Is) generated by the electric machine (EM) at the corresponding torque (BM) and regulate the generator current (Is) of the electric machine in such a way that the electric power (P) of the electric machine (EM) can be reduced during the movement of the traction drive. el ) is at least limited to a predetermined minimum value.

Description

Technical Field

[0001] The invention relates to a control system for an electric machine for generating a braking torque by means of the electric machine and to a method for operating a control system for an electric machine. Background Art

[0002] For electrically operated vehicles, the electric motor generates regenerative energy during the movement of the electric vehicle, which is generated from the kinetic energy of the vehicle's dynamics. The generated regenerative energy is mostly transmitted as electrical energy to the loads and batteries in the vehicle. In the event that the battery is no longer able to receive energy because it is fully charged, defective or not connected, the energy flow to the battery should be suppressed. Usually, the electric motor itself cannot generate a braking torque without supplying power to the battery or the load.

[0003] On the other hand, in the case of a long downhill trip or when driving with a trailer load, an additional braking torque of the machine may be required in order to unload the brake system. If the electric motor itself cannot generate the additional braking torque, the conventional brake system must be designed to be very large.

[0004] DE 10 2010 054 452 A1 describes a brake control device for an electric vehicle, which calculates a target braking torque based on the wheels. The brake control device can implement ABS control. The brake control device can include a battery for storing regenerated energy and generate a motor torque command based on the charge state. Summary of the invention

[0005] The invention provides a control system for an electric machine for generating a braking torque by means of the electric machine as claimed in claim 1 and a method for operating a control system for an electric machine as claimed in claim 10 .

[0006] Preferred developments are the subject matter of the dependent claims.

[0007] The invention is based on the idea of ​​providing a control system for an electric machine for generating a braking torque by means of the electric machine and a method for operating a control system for an electric machine so that even if the battery of the vehicle is defective, fully charged or not connected, a controlled braking torque can still be generated by means of the electric machine without any electrical power being output or the electrical power being able to be kept within a predetermined value range. The mechanical brake can be relieved by means of this additional braking torque.

[0008] According to the invention, a control system for an electric machine for generating a braking torque at a traction drive via the electric machine comprises a control device, wherein the control device is designed to ascertain a torque of the electric machine and a generator current generated by the electric machine at a corresponding torque and thereafter regulate the generator current of the electric machine in such a way that the electrical power of the electric machine can be limited to at least a predetermined minimum value during a movement of the traction drive.

[0009] The control system is advantageously suitable for electric vehicles and hybrid vehicles. The electrical power that can be fed into a DC circuit, for example a battery for an electric drive, can advantageously be kept below a certain value or at zero.

[0010] According to a preferred specific embodiment of the control system, the control device is designed to calculate a generator current as a function of the respective torque generated by the electric machine or to ascertain the generator current from a characteristic diagram as a function of the respective rotational speed and the respective torque of the electric machine.

[0011] The braking torque can advantageously be generated by the electric machine if the electrical power is zero or close to zero and the associated generator voltage is equal to zero or close to zero (below a predetermined limit value).

[0012] According to a preferred embodiment of the control system, the control device comprises a power regulation device which is designed to generate a current phase angle of the generator current in such a way that the electrical power of the electric machine can be limited to below a predetermined minimum value or can be set to zero.

[0013] According to a preferred embodiment of the control system, the control device includes a current regulating device, which is designed to: receive the determined values ​​for the generator current and the corresponding values ​​of the current phase angle for the corresponding determined speed of the motor and regulate them according to the determined speed in such a way that a generator voltage and the corresponding voltage phase angle are generated in the motor, so that the electrical power of the motor can be limited to below a predetermined minimum value or can be set to zero.

[0014] According to a preferred specific embodiment of the control system, the current phase angle and / or the voltage phase angle can be generated in such a way that the cosine of the difference between the two phase angles is equal to zero.

[0015] According to a preferred embodiment of the control system, the phase angle between the generator current and the generator voltage is +90° or −90°.

[0016] According to a preferred specific embodiment of the control system, the current regulator is connected to the electric machine and the generator current generated at the electric machine after regulation by the current regulator can be applied to the current regulator again as an input variable for the current regulator.

[0017] According to a preferred embodiment of the control system, the control device is configured to determine the electric power generated by the motor from the generator current generated at the motor and / or from a value of the voltage phase angle correspondingly related to the generated generator current and / or from a value of the generator voltage correspondingly related to the generated generator current, and to use the electric power generation as an input variable for a power control device.

[0018] According to a preferred specific embodiment of the control system, the control device is designed to ascertain a maximum generator current that can be generated by the electric machine and to ascertain a maximum torque associated with this maximum generator current and to take this into account during regulation.

[0019] According to the invention, in the method for operating a control system for an electric machine, a torque of the electric machine and a generator current generated by the electric machine at a corresponding torque are ascertained, and the generator current of the electric machine is regulated in such a way that during a movement of the traction drive the electrical power of the electric machine is limited to at least a predetermined minimum value and a braking torque is generated at the traction drive by the electric machine.

[0020] According to a preferred specific embodiment of the method, the power regulating device of the control device generates a current phase angle relative to the generator current in such a way that the electrical power of the electric machine can be limited to below a predetermined minimum value or can be set to zero.

[0021] According to a preferred embodiment of the method, the current regulating device receives the determined values ​​for the generator current and the associated values ​​for the current phase angle for the correspondingly determined rotational speed of the motor, and regulates the generator current according to the determined rotational speed in such a way that a generator voltage and the associated voltage phase angle are generated in the motor, so that the electrical power of the motor can be limited to below a predetermined minimum value or can be set to zero.

[0022] According to a preferred specific embodiment of the method, the current regulator is connected to the electric machine and the generator current generated at the electric machine after regulation by the current regulator is applied to the current regulator again as an input variable for the current regulator.

[0023] According to a preferred embodiment of the method, the control device determines the electric power generated by the electric motor from the generator current generated at the electric motor and / or from a value of the voltage phase angle correspondingly related to the generated generator current and / or from a value of the generator voltage correspondingly related to the generated generator current, and uses the electric power generation as an input variable for a power control device.

[0024] The method can also advantageously be distinguished by already mentioned features and advantages thereof being combined with the control system and vice versa.

[0025] Further features and advantages of embodiments of the present invention are apparent from the following description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention is explained in more detail below with reference to an exemplary embodiment illustrated in the schematic representation of the drawing.

[0027] in:

[0028] Figure 1 A schematic diagram showing a control system for a motor in an electric vehicle according to an embodiment of the present invention; and

[0029] Figure 2 A schematic block diagram of a control system according to another embodiment of the present invention is shown. DETAILED DESCRIPTION

[0030] In the figures, the same reference symbols denote identical elements or elements having the same function.

[0031] Figure 1 A schematic diagram of a control system for an electric motor in an electric vehicle according to an embodiment of the present invention is shown.

[0032] In an electric vehicle F or a hybrid vehicle, a traction drive T may be present, which may be driven by an electric machine EM. In addition to a mechanical brake, the electric machine may also advantageously generate a braking torque in such a way that the battery is not charged by recuperation energy.

[0033] To this end, the generator voltage can be set equal to or close to zero so that the electrical power P el Keep close to or equal to zero. In order to achieve this, the motor can be connected to a control system 10.

[0034] Figure 2 A schematic block diagram of a control system according to another embodiment of the present invention is shown.

[0035] The control system 10 for the electric machine EM comprises a control device SE for generating a braking torque at the traction drive by means of the electric machine EM, wherein the control device SE is designed to ascertain a torque BM of the electric machine EM and to ascertain a generator current Is generated by the electric machine EM at a corresponding torque BM and thereafter to regulate the generator current Is of the electric machine in such a way that an electrical power P of the electric machine EM can be reduced during a movement of the traction drive. el At least below a predetermined minimum value.

[0036] The torque BM can be calculated as follows:

[0037] ,in,

[0038] Np is the number of pole pairs of the motor, FM is the flux of the permanent magnet, Iq is the current in the direction of torque formation, Ld is the inductance in the d direction, and Lq is the inductance in the q direction.

[0039] According to the field-oriented regulation commonly used for synchronous machines, the d-direction is referred to as the field-forming direction and the q-direction is referred to as the transverse direction or torque-forming direction.

[0040] In this case, the control device SE can be configured to determine the rotational speed D of the electric machine EM, advantageously to read out the rotational speed from monitoring of the operation of the electric machine, and to determine therefrom a characteristic diagram KF for the generator current Is generated by the electric machine EM as a function of the rotational speed D (phase and current are functions of the rotational speed in this case).

[0041] The control device SE can further be designed to determine the current phase angle φ associated with the generator current Is as a function of the rotational speed D from the characteristic diagram KF. I , that is, identifying in which phase the current is at the current rotor angle.

[0042] In this case, the control device SE can be designed to calculate the generator current Is as a function of the respective torque BM generated by the electric machine EM or to ascertain the generator current from a characteristic diagram KF as a function of the respective rotational speed D of the electric machine EM and the respective torque BM.

[0043] The control device SE can include a power control device R which is designed to generate a current phase angle φ of the generator current Is in such a way that I , so that the electric power P of the motor EM el Can be limited below a predetermined minimum value or can be set to zero.

[0044] The control device SE can include a current regulator StR which can be designed to receive in each case an ascertained value for the generator current Is and a current phase angle φ for a respectively ascertained rotational speed D of the electric machine EM. I and, depending on the ascertained rotational speed D, is adjusted in such a way that a generator voltage Us and an associated voltage phase angle φ are generated in the electric machine EM. U , so that the electric power P of the motor EM el Can be limited below a predetermined minimum value or can be set to zero.

[0045] The current phase angle φ I and / or voltage phase angle φ U It can be produced in such a way that the cosine of the difference of the two phase angles is equal to zero. In this case, the electrical power for the battery circuit (DC circuit) can be equal to zero.

[0046] Phase Angle The generator current Is can be between + 90° or - 90° to the generator voltage Us, so that for example And also through The electrical power can be equal to zero. As a result, advantageously only power losses, for example for field weakening or field strengthening, are generated. Here, the magnetic field of the permanent magnet can be weakened or strengthened by the magnetic field of the stator (the current of the stator receives a positive (field strengthening) or negative (field weakening) component in the d direction).

[0047] Thus, it is also possible to A braking torque is generated under the condition that the electric power can be equal to zero.

[0048] In this case, the generator voltage Us can advantageously be set equal to zero and the generator current Is can therefore be regulated in the current regulating device StR in such a way that the electrical power ,in , where φ UMI Can be φ U With φ I The angular difference between them, and the two phase angles can be expressed along the direction of field formation and torque formation.

[0049] The current Is can be regulated, for example, using a standard regulator with field-oriented regulation or the like.

[0050] The current regulator StR can be connected to the electric machine EM and the generator current Is_i generated at the electric machine EM after regulation by the current regulator StR can be applied to the current regulator again as an input variable for the current regulator StR.

[0051] Furthermore, the control device SE can be designed for the control system 10 to generate a generator current Is_i generated at the operating electric machine EM and at its output in a corresponding control step and / or to generate a voltage phase angle φ U The generated electrical power P of the electric machine (actually output at the output in the corresponding control step) is determined from the value of the generator voltage Us correspondingly dependent on the generated generator current Is_i (the voltage Us belonging to the controller and specified or calculated in order to set the electrical power to zero) el , and the electrical power is generated as an input variable for the power control device LR.

[0052] The generation of the new input variable can be realized in the sense of a feedback control loop, advantageously using the current Is-i actually present at the electric machine EM in order to ascertain the actual instantaneous electrical power of the electric machine EM and to determine the actual instantaneous electrical power P relative to the desired power P el =0. Such a control loop can be implemented by a control device SE. For this purpose, other variables such as, for example, the generator voltage Us and its phase angle φu can also be taken into account. For this purpose, the control device SE can be set up to: generate the generator current Is_i at the electric machine EM and / or the voltage phase angle φ U The generated electrical power P of the electric machine is determined from the value of the generator voltage Us which is respectively dependent on the generated generator current Is_i and / or from the value of the generator voltage Us which is respectively dependent on the generated generator current Is_i. el -i and uses this electric power generation as an input variable for a power control device LR in order to readjust the phase position of the generator current.

[0053] Control device SE can be designed to ascertain a maximum generator current Is_max that can be generated by electric machine EM and to ascertain a maximum torque BM_max associated with this maximum generator current Is_max that can be generated and to take this into account during control.

[0054] according to The generator current can be calculated where BM_des is the torque desired by the vehicle control system or the driver, omega is the electrical rotational speed, np is the number of pole pairs, and R is the resistance (of the motor). The power losses at the stator resistance can be calculated here, which can be calculated by to achieve.

[0055] Therefore, the electrical power P of the electric machine EMel Can be limited below a predetermined minimum value or can be set to zero.

[0056] In this case, the electric machine can include an inverter, on which a corresponding modulation can be applied, for example also by means of a conversion element (I / O).

[0057] The predetermined minimum value can be used to ensure that sufficiently little power flows into the DC circuit for the battery, but this sufficiently little power can particularly advantageously be equal to zero.

[0058] for Then it can be concluded that, Change to P el = 0 or at least remain below the tolerable limit.

[0059] However, it is possible that deviations of these variables from specific variables may occur and that a tolerable, predetermined limit value may therefore be set for the resulting power (actually ascertained in an iteration step) and that the power may then be kept below this limit value.

[0060] By regulating the current, for example, by the current regulator StR, the torque of the electric machine can then also be regulated as a direct result.

[0061] By means of such a control, a torque can also be provided which generates no or almost no vibrations in the drive train, ie shocks in the torque can be reduced or avoided.

[0062] Although the invention has been fully described above with reference to preferred exemplary embodiments, it is not restricted thereto but can be modified in many ways and methods.

Claims

1. A control system (10) for an electric machine (EM), the control system being used to generate a braking torque at a traction drive by means of the electric machine (EM), the control system comprising: a control device (SE), wherein the control device (SE) is designed to ascertain the torque (BM) of the electric machine (EM) and to ascertain the generator current (Is) generated by the electric machine (EM) at the corresponding torque (BM), and thereafter to regulate the generator current (Is) of the electric machine in such a way that the electrical power (P) of the electric machine (EM) can be reduced during the movement of the traction drive. el ) is at least limited to a predetermined minimum value and a braking torque is generated at the traction drive by the electric machine, wherein the control device (SE) comprises a power regulation device (LR) which is designed to generate a current phase angle (Phi_I) of the generator current (Is) in such a way that the electric power (P el ) can be limited below the predetermined minimum value or can be set to zero, wherein the control device (SE) includes a current regulating device (StR), which is designed to: receive the determined values ​​for the generator current (Is) and the associated values ​​of the current phase angle (Phi_I) for the correspondingly determined speed (D) of the electric machine (EM) and regulate it according to the determined speed (D) in such a way that a generator voltage (Us) and the associated voltage phase angle (Phi_U) are generated in the electric machine (EM), so that the electrical power (P el ) can be limited to below a predetermined minimum value or can be set to zero.

2. A control system (10) according to claim 1, wherein the control device (SE) is configured to calculate a generator current (Is) associated with a corresponding torque (BM) generated by the electric motor (EM), or to determine the generator current from a characteristic curve group (KF) associated with a corresponding rotational speed (D) and a corresponding torque (BM) of the electric motor (EM).

3. The control system (10) according to claim 1 or 2, wherein the current phase angle (Phi_I) and / or the voltage phase angle (Phi_U) can be generated in such a way that the cosine of the difference between the two phase angles is equal to zero.

4. The control system (10) according to claim 3, wherein the phase angle (Phi_UM) between the generator current (Is) and the generator voltage (Us) is +90° or -90°.

5. A control system (10) according to claim 1 or 2, wherein the current regulator (StR) is connected to the motor (EM), and the generator current (Is_i) generated on the motor (EM) after regulation by the current regulator (StR) can be loaded again on the current regulator as an input variable for the current regulator (StR).

6. A control system (10) according to claim 5, wherein the control device (SE) is designed to determine the generated electrical power (P s_i) of the electric machine from the generator current (Is_i) generated at the electric machine (EM) and / or from a value of the voltage phase angle (Phi_U) correspondingly related to the generated generator current (Is_i) and / or from a value of the generator voltage (Us) correspondingly related to the generated generator current (Is_i) el -i), and the electrical power generation is used as an input variable for the power control device (LR).

7. A control system (10) according to claim 1 or 2, wherein the control device (SE) is configured to: determine the maximum generator current (Is_max) that can be generated by the electric motor (EM) and determine the maximum torque (BM_max) associated with this maximum generator current (Is_max) that can be generated and take this into account during regulation.

8. A method for operating a control system (10) for an electric machine (EM), the method comprising the following steps: - determining (S1) a torque (BMs) of the electric machine (EM) and a generator current (Is) generated by the electric machine (EM) at the corresponding torque (BM); - regulating (S2) the generator current (Is) of the electric machine in such a way that the electric power (P el ) is at least limited to a predetermined minimum value and a braking torque is generated at the traction drive by the electric machine, wherein a power regulation device (LR) of a control device (SE) generates a current phase angle (Phi_I) associated with the generator current (Is) in such a way that the electric power (P el ) can be limited to a predetermined minimum value or can be set to zero, wherein the current control device (StR) receives the determined values ​​for the generator current (Is) and the associated values ​​for the current phase angle (Phi_I) for the respectively determined rotational speed (D) of the electric machine (EM), and regulates the generator current (Is) as a function of the determined rotational speed (D) in such a way that a generator voltage (Us) and an associated voltage phase angle (Phi_U) are generated in the electric machine (EM), so that the electrical power (P el ) can be limited to below a predetermined minimum value or can be set to zero.

9. A method according to claim 8, wherein the current regulator (StR) is connected to the electric motor (EM), and after regulation by the current regulator (StR), the generator current (Is_i) generated at the electric motor (EM) is loaded onto the current regulator again as an input variable for the current regulator (StR).

10. The method according to claim 9, wherein the control device (SE) determines the generated electrical power (P s_i) of the electric machine from the generator current (Is_i) generated at the electric machine (EM) and / or from a value of the voltage phase angle (Phi_U) which is respectively related to the generated generator current (Is_i) and / or from a value of the generator voltage (Us) which is respectively related to the generated generator current (Is_i) el -i), and the electrical power generation is used as an input variable for the power control device (LR).

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