METHOD AND DEVICE FOR DETERMINING THE POSITION AND SPEED OF A ROTOR OF AN ELECTRIC MACHINE

Description

[0001] The present invention relates to a method for determining the position and rotational speed of a rotor of an electric machine during an active short circuit and a corresponding rotor state determination device.

[0002] Electrical machines, such as permanent magnet synchronous machines, are used in numerous technical fields. For example, such permanent magnet synchronous machines are used in motor vehicles, especially electric and hybrid vehicles. State of the art

[0003] WO 2016 / 066330 discloses a method and a device for switching from the freewheeling operating state of an electric machine to a short-circuit operating state.

[0004] The invention is based on the fact that, in the event of a failure of the rotor position sensors, the electric machine switches to emergency operation at a rotor speed within a defined emergency operating speed range. To prevent damage to the electric machine, an active short circuit is automatically activated above this emergency operating speed. However, this prevents the electric machine from operating in emergency mode.

[0005] It is therefore the object of the present invention to provide a method and a device with which, in the event of a failure of rotor position sensors, the position and rotational speed of the rotor of an electric machine can be determined during an active short circuit, so that a safe transition to emergency operation is possible.

[0006] The publications EP 1 195 611 A1; DE 10 2016 210238 A1; DE 10 2013 112169 disclose different methods and devices for determining the position and speed of electrical machines in different applications. Disclosure of the invention

[0007] The problem is solved by a method for determining the position and rotational speed of a rotor of an electric machine during an active short circuit, comprising the features of claim 1. Regarding a device for carrying out such a method, reference is made to claim 5. The dependent claims relating back to claim 1 describe advantageous embodiments of the invention.

[0008] The method according to the invention comprises the steps of determining the short-circuit currents resulting from the short circuit, determining a total current resulting from the short-circuit currents, determining a stator current angle of the total current with respect to a stator coordinate system, and determining a rotor current angle of the total current with respect to a flux direction of the rotor. This includes the steps of calculating the magnitude of the total current, determining the rotor current angle based on a characteristic relationship between the magnitude of the total current and a rotor current angle established for the electrical machine, wherein the rotor position corresponds to the sum of the stator current angle and the rotor current angle, and wherein the rotor speed is obtained from monitoring the rotor position.

[0009] In the context of the present invention, the position of the rotor is understood to be its position relative to the stator. This position is preferably expressed as an angle. Accordingly, the rotational speed of the rotor is also understood to be the relative movement of the rotor to the stator. The stator current angle and rotor current angle are understood to be the angle between the stator and rotor, respectively, and the total current.

[0010] The advantage of the invention lies in the fact that the rotor position and speed can be determined even if the rotor position sensors fail. This allows the electric machine to be safely switched to emergency operation during an active short circuit. Upon reaching an emergency running speed, emergency operation can thus be initiated without damaging the electric machine.

[0011] In a preferred embodiment of the invention, the characteristic relationship is determined by relating the speed-dependent values ​​of the total current (in magnitude) and the rotor current angle. This makes it possible to calculate the rotor current angle by determining the total current (in magnitude).

[0012] In a further preferred embodiment of the invention, a rotor position smoothing value is determined by smoothing a multitude of rotor position values. This minimizes inaccuracies caused by large deviations in individual values. Measurement noise is thereby reduced, thus increasing the accuracy of the determined rotor position.

[0013] The method preferably includes a step in which the determined rotor position and / or rotor speed is compared with sensor information. This allows a sensor defect to be verified again.

[0014] The invention further comprises a rotor state determination device which is configured to carry out the method according to the invention.The rotor state determination device comprises a current determination unit for determining the short-circuit currents resulting from a short circuit, a total current determination unit for determining a total current resulting from the short-circuit currents, a stator current angle determination unit for determining a stator current angle of the total current relative to a stator coordinate system, a rotor current angle determination device for determining a rotor current angle of the total current relative to a flux direction of the rotor, wherein the rotor current angle determination device comprises a calculation unit for calculating a magnitude of the total current, and a current angle correlation unit for determining the rotor current angle correlated to the magnitude of the total current, a rotor position determination unit for determining a rotor position, and a rotor speed determination device for determining a rotor speed.

[0015] The inventive method can be carried out using the rotor state determination device, so that the advantages mentioned for this method can be achieved.

[0016] In a preferred embodiment, the rotor speed determination device includes a smoothing unit. This smoothing unit can be used to smooth the rotor position values, thereby increasing the accuracy of the determined rotor position values.

[0017] In another preferred embodiment, the electric machine is a permanent magnet synchronous machine, an electrically excited synchronous machine, or a synchronous reluctance machine. The permanent magnet synchronous machine has the advantage of high efficiency and a compact design. The synchronous reluctance machine has the advantage that, unlike permanent magnet synchronous motors, its manufacture does not require the use of magnetic materials based on so-called rare earth elements. Furthermore, the synchronous reluctance machine exhibits virtually no rotor losses, resulting in good efficiency.

[0018] Preferably, the electric machine is three-phase. The advantage of such electric machines is that they exhibit high dynamics, high torque, and high efficiency.

[0019] To carry out the method according to the invention, the invention comprises a computer program product with program code means for carrying out the method when the computer program product is installed on a control unit of a rotor state determination device.

[0020] Furthermore, the invention comprises a machine-readable storage medium on which the computer program product is stored.

[0021] Exemplary embodiments of the invention are shown in the drawing and explained in more detail in the following description. It shows: Figure 1 Exemplary embodiment of a method and a rotor state determination device for determining the position and speed of a rotor of an electric machine, Figure 2 Graphical representation of a position determination of a rotor relative to a stator using the example of a three-phase electric machine, Figure 3 Diagrams for deriving a characteristic dependence between the magnitude of the total current and a rotor current angle, and Figure 4 Diagram of the characteristic dependence between the magnitude of the total current and a rotor current angle.

[0022] Figure 1Figure 1 shows an embodiment of a method and an embodiment of a rotor state determination device 10 for determining the position ΘR and rotational speed nR of a rotor (not shown) of an electric machine (not shown). In a current determination unit 14, the short-circuit currents IU, IVI, IW resulting during an active short circuit are determined using the example of a three-phase electric machine. The resulting short-circuit currents IU, IVI, IW are shown in Figure 2 The following is shown. In a total current determination unit 18 of the rotor state determination device 10, a total current Iα, Iβ resulting from the short-circuit currents IU, IV, IW is then determined. A graphical determination of the total current Iα, Iβ from the short-circuit currents IU, IV, IW, offset by 120° for a three-phase motor, is shown in Figure 2 depicted.

[0023] A stator current angle determination unit 22 determines a current angle ψ I, which is defined as a stator current angle ψ I and in Figure 2 The angle shown is that of the total current Iα, Iβ relative to a stator coordinate system α, β. This stator current angle ψI indicates the direction of the total current Iα, Iβ relative to the stator coordinate system α, β. The rotor state determination device 10 additionally comprises a rotor current angle determination device 26, which includes a calculation unit 30 in which a magnitude I of the total current Iα, Iβ is calculated.

[0024] Furthermore, the rotor current angle determination device 26 includes a current angle correlation unit 34, which determines a rotor current angle φ I based on a characteristic dependence created for the electrical machine between the total current I determined by the calculation unit 30 and a rotor current angle φ I.

[0025] As in Figure 2As shown, the rotor current angle φI indicates the angle between the total current Iα, Iβ and a flux direction dR of the rotor. The rotor state determination device 10 additionally includes a rotor position determination unit 38, which calculates the rotor position ΘR from a sum of the stator current angle ψI and the rotor current angle φI. The rotor position ΘR corresponds, as shown in Figure 2 The angle between the flux direction d R of the rotor and the stator is shown. The rotor speed n R is determined by monitoring the rotor position Θ R using a rotor speed determination device 42.

[0026] From a large number of rotor position values ​​ΘR and rotor speed values ​​nR, a rotor position smoothing value ΘRg and a rotor speed smoothing value nRg are calculated in a smoothing unit 46. This allows inaccuracies caused by large deviations in individual values ​​to be minimized.

[0027] Figure 3The diagrams show the derivation of a characteristic relationship between the total current I and a rotor current angle φI. For this purpose, the total current I and the rotor current angle φI, calculated from the total current Iα and Iβ, were determined for an electric machine as a function of the machine speed n. These speed-dependent values ​​are different for each electric machine and characterize it.

[0028] Using the same machine speed values ​​n, the total current I and the rotor current angle φ I can be related to each other without knowing the rotational speed. Such a relationship between the two values ​​is shown in Figure 4The characteristic relationship between the total current I and the rotor current angle φI is shown in this figure. Using this diagram, the current-angle correlation unit 34 determines the corresponding rotor current angle φI based on the total current I.

Claims

1. Method for determining a position (ΘR) and rotational speed (nR) of a rotor of an electric machine during an active short circuit, wherein the rotor position (ΘR) of the rotor corresponds to the angle between the direction of flow (dR) of the rotor and the stator, wherein the method comprises the steps: - determining the short circuit currents (IU, IV, IW) occurring during the short circuit, - determining a total current (Iα, Iβ), arising from the short circuit currents (IU, IV, IW), - determining a stator current angle (ψl) of the total current (Iα, Iβ) with respect to a stator coordinate system (α, β), characterized by the steps of: - determining a rotor current angle (ϕI) of the total current (Iα, Iβ) with respect to a direction of flow (dR) of the rotor, wherein this step comprises the steps: - calculating an absolute-value variable (I) of the total current (Iα, Iβ), - determining the rotor current angle (ϕI) on the basis of a characteristic dependence, produced for the electric machine, between the absolute-value total current (I) and a rotor current angle (ϕI), wherein the rotor position (ΘR) corresponds to a sum of the stator current angle (ψI) and the rotor current angle (ϕI), and wherein the rotor rotational speed (nR) is obtained from monitoring the rotor position (ΘR).

2. Method for determining a position (ΘR) and rotational speed (nR) of a rotor of an electric machine according to Claim 1, characterized in that the characteristic dependence is determined by relating to one another the rotational-speed-dependent values of absolute-value total current (I) and of the rotor current angle (ϕI).

3. Method for determining a position (ΘR) and rotational speed (nR) of a rotor of an electric machine according to Claim 1 or 2, characterized in that a rotor position smoothed value (ΘRg) is determined from smoothing a multiplicity of rotor position values (ΘR).

4. Method for determining a position (ΘR) and rotational speed (nR) of a rotor of an electric machine according to one of the preceding claims, characterized in that the method comprises a step in which the determined rotor position (ΘR) and / or rotor rotational speed (nR) are / is compared with sensor information.

5. Rotor state-determining device (10) for determining a position (ΘR) and rotational speed (nR) of a rotor of an electric machine during an active short circuit, wherein the rotor position (ΘR) of the rotor corresponds to the angle between the direction of flow (dR) of the rotor and the stator, wherein the rotor state-determining device (10) configured to carry out the method according to one of the preceding claims, comprising: - a current-determining unit (14) for determining the short circuit currents (IU, IV, IW) which occur during the short circuit, - a total current-determining unit (18) for determining a total current (Iα, Iβ), which results from the short circuit currents (IU, IV, IW), - a stator current angle-determining unit (22) for determining a stator current angle (ψI) of the total current (Iα, Iβ) with respect to a stator coordinate system (α, β), characterized by - a rotor current angle-determining device (26) for determining a rotor current angle (ϕI) of the total current (Iα, Iβ) with respect to a direction of flow (dR) of the rotor, wherein the rotor current angle-determining device (26) comprises - a calculation unit (30) for calculating an absolute-value variable (I) of the total current (Iα, Iβ), and - a current angle-correlation unit (34) for determining the rotor current angle (ϕI) which is correlated with the absolute-value total current (I), - a rotor position-determining unit (38) for determining a rotor position (ΘR), - a rotor rotational speed-determining device (42) for determining a rotor rotational speed (nR).

6. Rotor state-determining device (10) according to Claim 5, characterized in that the rotor rotational speed-determining device (42) comprises a smoothing unit (46).

7. Rotor state-determining device (19) according to Claim 5 or 6, characterized in that the electric machine is a permanent magnet synchronous machine, an electrically excited synchronous machine or a synchronous reluctance machine.

8. Rotor state-determining device (10) according to one of Claims 5 to 7, characterized in that the electric machine has three phases.

9. Computer program product having program code means for carrying out the method according to one of Claims 1 to 4 when the computer program product runs on a control unit (14, 18, 22, 26, 38, 42) of a rotor state-determining device (10) according to one of Claims 5 to 8.

10. Machine-readable storage medium on which the computer program product according to Claim 9 is stored.