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

Abstract

The present invention relates to a control system (10) for an electric machine (EM), for producing a braking torque, by means of the electric machine (EM), in a traction drive, said system comprising a control device (SE), the control device (SE) being configured to control a generator voltage or a generator current in or through a power electronics system (LE) of the electric machine such that during a movement of the traction drive, the electric power (Pel) of the electric machine (EM) can be limited to a level at least below a predefined minimum value.

Claims

1. A control system (10) for an electric machine (EM) for generating a braking torque by means of the electric machine (EM) in a traction drive, the control system comprising: a control facility (SE), wherein the control facility (SE) is configured to control a generator voltage or a generator current in or by means of an electronic power system (LE) of the electric machine in such a manner that during a movement of the traction drive an electrical power (Pei) of the electric machine (EM) can be limited at least to a predetermined minimum value.

2. The control system (10) as claimed in claim 1, wherein the control facility (SE) comprises a switch unit (S) which is connected to machine clamps and/or to the electronic power system (LE) and which is configured to switch a short circuit at the machine clamps and/or at the electronic power system (LE).

3. The control system (10) as claimed in claim 1, wherein the control facility (SE) is configured to determine a rotational speed (D) of the electric machine (EM) and to calculate or generate therefrom a generator current (Is) that is generated by the electric machine (EM) in such a manner that an electrical power (P.sub.el) of the electric machine (EM) that is associated with the generator current (Is) can be achieved as less than a predetermined limit value or equal to zero.

4. The control system (10) as claimed in claim 1, wherein the control facility (SE) is configured to determine a rotational speed (D) of the electric machine (EM) and to determine therefrom in dependence upon the rotational speed (D) a characteristic field (KF) for a generator current (Is) that is generated by the electric machine (EM), and to determine the generator current (Is) in dependence upon the rotational speed (D) from the characteristic field (KF).

5. The control system (10) as claimed in claim 3, wherein the control facility (SE) is configured to determine from the characteristic field (KF) in dependence upon the rotational speed (D) a current phase angle (ϕ.sub.I) that is associated with the generator current (Is).

6. The control system (10) as claimed in claim 3, wherein the control facility (SE) comprises a power control facility (LR) that is configured to generate a current phase angle (ϕ.sub.I), which is associated with the generator current (Is), in such a manner that the electrical power (P.sub.el) of the electric machine (EM) is limited to below the predetermined minimum value or can be set to zero.

7. The control system (10) as claimed in claim 3, wherein the control facility (SE) comprises a current control facility (StR) that is configured for the respectively determined rotational speed of the electric machine (EM) to receive in each case the determined value for the generator current (Is) and the associated current phase angle (ϕ.sub.U-ϕ.sub.I) and in dependence upon the determined rotational speed (D) to control it in such a manner that a generator voltage (Us) and an associated voltage phase angle (ϕU) are generated in the electric machine (EM) with the result that the electrical power (P.sub.el) of the electric machine (EM) is limited to below the predetermined minimum value or can be set to zero.

8. The control system (10) as claimed in claim 7, wherein the current control facility (StR) is connected to the electric machine (EM) and a generator current (Is_i) that results after the control procedure by means of the current control facility (StR) in the electric machine (EM) can be applied thereto afresh as an input variable for the current control facility (StR).

9. The control system (10) as claimed in claim 8, wherein the control facility (SE) is configured, from the generator current (Is_i) that results at the electrical machine (EM), and/or from the value of the voltage phase angle (ϕ.sub.U) that is associated respectively with the resulting generator current (Is_i), and/or from the value of the generator voltage (Us) that is associated respectively with the resulting generator current (Is_i), to determine a resulting electrical power (P.sub.el-i) of the electric machine and to generate it as an input variable for the power control facility (LR).

10. A method for operating a control system (10) for an electric machine (EM), the method comprising the steps: controlling (S1) a generator voltage or a generator current in or by means of a power electronics system (LE) of the electric machine in such a manner that during a movement of the traction drive an electrical power (P.sub.el) of the electric machine (EM) can be limited at least to a predetermined minimum value and in this case a braking torque is generated by means of the electric machine in the traction drive.

11. The method as claimed in claim 10, wherein the control facility (SE) determines a rotational speed (D) of the electric machine (EM) and determines therefrom in dependence upon the rotational speed (D) a characteristic field (KF) for a generator current (Is) that is generated by the electric machine (EM).

12. The method as claimed in claim 11, wherein a power control facility (LR) generates a current phase angle (Phi_I), which is associated with the generator current (Is), in such a manner that the electrical power (P.sub.el) of the electric machine (EM) is limited to below the predetermined minimum value or is set to zero.

13. The method as claimed in claim 10, wherein a current control facility (StR) receives for the respectively determined rotational speed of the electric machine (EM) in each case the determined value for the generator current (Is) and the associated current phase angle (ϕ.sub.I) and in dependence upon the determined rotational speed (D) controls the electric machine (EM) in such a manner that a generator voltage (Us) and an associated voltage phase angle (ϕ.sub.U) are generated in the electric machine (EM) with the result that the electrical power (P.sub.el) of the electric machine (EM) is limited to below the predetermined minimum value or is set to zero.

14. The method as claimed in claim 13, wherein a generator current (Is_i) that results after the control procedure by means of the current control facility (StR) in the electric machine (EM) is applied thereto afresh as an input variable for the current control facility (StR).

15. The method as claimed in claim 14, wherein, from the generator current (Is_i) that results in the electric machine (EM) and/or from the value of the voltage phase angle (ϕ.sub.U) that respectively is associated with the resulting generator current (Is_i) and/or from the value of the generator voltage (Us) that respectively is associated with the resulting generator current (Is_i), the control facility (SE) determines a resulting electrical power (P.sub.el-i) of the electric machine and generates it as an input variable for the power control facility (LR).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is further explained below with the aid of the exemplary embodiment that is disclosed in the schematic figures of the drawing.

(2) In the drawing:

(3) FIG. 1 illustrates a schematic view of a control system for an electric machine in accordance with an exemplary embodiment of the present invention in an electric vehicle;

(4) FIG. 2 illustrates a schematic block diagram of a control system in accordance with a further exemplary embodiment of the present invention;

(5) FIG. 3 illustrates a schematic block diagram of a control system in accordance with a further exemplary embodiment of the present invention; and

(6) FIG. 4 illustrates a schematic block diagram of a control system in accordance with a further exemplary embodiment of the present invention.

(7) In the figures, like reference numerals describe like or like-functioning elements.

DETAILED DESCRIPTION

(8) FIG. 1 illustrates a schematic view of a control system for an electric machine in accordance with an exemplary embodiment of the present invention in an electric vehicle.

(9) An electric vehicle F or a hybrid vehicle can have a traction drive T that can be driven by an electric machine EM. In addition to a mechanical brake, the electric machine can also advantageously generate a braking torque in such a manner that the battery is not charged by the recuperation energy. For this purpose, it is possible to set a generator voltage to be equal to or close to zero in order to be able to keep the electrical power P.sub.el close to or equal to zero. In order to be able to implement this, the electric machine is connected to a control system 10.

(10) The control facility in the control system 10 can comprise a switch unit S which is connected to machine clamps and/or to the electronic power system of the electric machine EM and which is configured so as to switch a short circuit at the machine clamps and/or at the electronic power system.

(11) FIG. 2 illustrates a schematic block diagram of a control system in accordance with a further exemplary embodiment of the present invention.

(12) The control system 10 for an electric machine EM comprises a control facility SE, wherein the control facility SE is configured so as to control a generator voltage or a generator current in or by means of an electronic power unit LE of the electric machine in such a manner that during a movement of the traction drive an electrical power P.sub.el of the electric machine EM can be limited at least to below a predetermined minimum value.

(13) In so doing, the control facility SE can be configured so as to determine a rotational speed D of the electric machine EM, in other words advantageously read it out from a monitoring procedure of the operation of the electric machine, and using a characteristic field KF to determine therefrom a generator current Is that is generated by the electric machine EM in dependence upon the rotational speed D (the phase and the current are in this case functions of the rotational speed). Furthermore, the control facility SE can be configured so as to determine a current phase angle ϕ.sub.I that is associated with the generator current Is from the characteristic field KF in dependence upon the rotational speed D, in other words to determine in which phase the current is in the case of the prevailing rotational speed.

(14) The control facility SE can furthermore comprise a current control facility StR which can receive in each case a value for the generator current Is and the associated current phase angle ϕ.sub.I from the control facility. The current control facility StR can be configured so as, for the respectively determined rotational speed of the electrical machine EM, to receive in each case the determined value for the generator current Is and the associated current phase angle ϕ.sub.I and in dependence upon the determined rotational speed D to perform a control procedure in such a manner that a generator voltage Us and an associated voltage phase angle ϕ.sub.U are generated in the electric machine EM (in other words the generator voltage Us and the associated phase ϕ.sub.U can be generated) with the result that the electrical power P.sub.el of the electric machine EM can be limited to below the predetermined minimum value or can be set to zero. In so doing, the electric machine can comprise an inverter on which it is possible to apply a corresponding modulation, possibly also having transformation elements (I/O).

(15) It is possible on the basis of the predetermined minimum value to ensure that sufficiently little power flows into the DC circuit for the battery, in particular said power can however be advantageously equal to zero.

(16) The current control facility StR can be connected to the electrical machine EM and a generator current Is_i (predominantly at the outlet of the electrical machine in the respective step) that results after the control procedure by means of the current control facility StR at the electric machine EM can be applied thereto afresh as an input variable for the current control facility StR. Thus, an iterative control loop can be achieved and, after an initial control procedure of the generator current and its phase so as to achieve the generator voltage Us and the associated phase ϕ.sub.U, it can be adjusted afresh with each step in such a manner in order in an adaptive manner to come closer to the conditions for an electrical power below the predetermined minimum value or at zero.

(17) In so doing, the generator voltage Us can be advantageously set to equal to zero.

(18) Alternatively or in addition thereto, the generator current Is can be controlled in such a manner in the current control facility StR that the electrical power P.sub.el=3*Us*Is*cos(ϕ.sub.UMI) is produced, with ϕ.sub.UMI=mod (ϕ.sub.U−ϕ.sub.I+π, 2*η)−π) as an angle difference between ϕ.sub.U and ϕ.sub.I, the two phase angles can be represented in a field-generating and torque-generating direction.

(19) Thus, P.sub.el of the electric machine EM can be below the predetermined minimum value or zero. The current can then be controlled for example using a standard controller with field-oriented control or similar.

(20) FIG. 3 illustrates a schematic block diagram of a control system in accordance with a further exemplary embodiment of the present invention.

(21) The embodiment illustrated in FIG. 3 differs from that of FIG. 2 to the extent that although the generator current Is or its value is provided in a similar manner to the embodiment in FIG. 2, its phase angle ϕ.sub.I is determined and generated in such a manner by the control facility SE that an electrical power P.sub.el of the electric machine EM that results from the generator current and its phase can be below the predetermined minimum value or at zero. Consequently, as described with reference to FIG. 2, the generator voltage and its phase can also be controlled based on these values. In iterative steps, an actual power P.sub.el can then be determined and the current phase angle ϕ.sub.I and/or the generator voltage and its phase adjusted afresh.

(22) For this purpose, the control facility SE can comprise a power control facility LR that is configured so as to generate a current phase angle ϕ.sub.I that is associated with the generator current Is in such a manner that the electrical power P.sub.el of the electric machine EM can be limited to below the predetermined minimum value or can be set to zero. In other words, in the case of the given length of the current Is, the phase angle of the current can be adjusted such that the electrical power is minimum or zero and such that no power or almost no power is flowing into the DC circuit, possibly of a battery. In so doing, the control facility SE can initially set a power that is to be achieved equal to zero and determine the resultant required phase for the determined generator current (determined from the rotational speed), advantageously generate it and transmit it as an input variable to the current control facility StR.

(23) Furthermore, the exemplary embodiment illustrated in FIG. 3 can also comprise a further feedback control loop, advantageously use the current Is-i that is actually prevailing at the electric machine EM in order to determine an actual prevailing electrical power of the machine EM and determine a difference with respect to the desired power P.sub.el=0. This control loop can be realized by means of the control facility SE. To that end, further variables, such as possibly the generator voltage Us and its phase angle ϕ.sub.u, can also be taken into consideration. For this purpose, the control facility SE can be configured so as, from the generator current Is_i that results in the electrical machine EM, and/or from the value of the voltage phase angle ϕ.sub.U that is associated respectively with the resulting generator current Is_i, and/or from the value of the generator voltage Us that is associated respectively with the resulting generator current Is_i, to determine a resulting electrical power P.sub.el-i of the electric machine and generate it as an input variable for the power control facility LR for a new control procedure of the phase of the generator current.

(24) FIG. 4 illustrates a schematic block diagram of a control system in accordance with a further exemplary embodiment of the present invention.

(25) The embodiment illustrated in FIG. 4 differs from that of FIG. 3 to the extent that, in lieu of the initial determination of the generator current Is for the respective rotational speed D, this is not determined from a characteristic field but rather a desired generator voltage Us′=0 can be specified, possibly by the control facility SE, which by means of a corresponding selection of the generator current Is can then lead to a minimized or diminishing electrical power P.sub.el (by determining the further variables as explained in FIG. 3). The control facility SE can thus be configured so as to determine a rotational speed D of the electric machine EM and to calculate or generate therefrom a generator current Is that is generated by the electric machine EM, in such a manner that an electrical power of the electric machine EM that is associated with the generator current Is can be generated as less than a predetermined limit value or equal to zero if these specific conditions of the voltages, currents and/or their phases are fulfilled.

(26) Theoretically, in the case of a generator voltage of Us=0, an electrical power equal to zero would then occur if the other variables according to P.sub.el=3*Us*Is*cos(ϕ.sub.UMI).

(27) For Us=0 or cos(ϕUMI)=0, it can then occur that P.sub.el=0 or at least below a limit value that is to be tolerated.

(28) However, deviations of these variables from the determined variables can occur and consequently a predetermined limit value which is to be tolerated can be set for the resulting power (actually determined in the iterative step), below which the power can then be maintained.

(29) By means of controlling the current, possibly by means of the current control facility StR, it is thus possible as a direct result therefrom to also control the torque of the electric machine. It is also possible by means of this control procedure to provide such a torque that does not generate any oscillations or generates almost no oscillations in the drive train, it is thus possible to reduce or avoid jerking in the torque.

(30) Although the present invention has been described in full with the aid of the preferred exemplary embodiment above, it is not limited thereto but rather can be modified in numerous ways.