Method and device for determining the position and the rotational speed of a rotor of an electric machine

Abstract

The invention relates to a method for determining the position (Θ.sub.R) and the rotational speed (n.sub.R) of a rotor of an electrical machine during an active short circuit and a rotor-state determining device (10) designed to carry out the method. The method comprises the steps of determining the short circuit currents (I.sub.u, I.sub.v, I.sub.w) resulting during the short circuit, determining a total current (I.sub.α, I.sub.β) resulting from the short circuit currents (I.sub.u, I.sub.v, I.sub.w), determining a stator current angle (ψ.sub.I) of the total current (I.sub.α, I.sub.β) with respect to a stator coordinate system (α, β), determining a rotor current angle (φ.sub.I) of the total current (I.sub.α, I.sub.β) with respect to a flux direction (d.sub.R) of the rotor, this step comprising the steps of calculating an amount variable (I) of the total current (I.sub.α, I.sub.β), determining the rotor current angle (φ.sub.I) on the basis of a characteristic dependence between the amount variable (I) and a rotor current angle (φ.sub.I), which dependence is created for the electrical machine, the rotor position (Θ.sub.R) corresponding to a sum of the stator current angle (ψ.sub.I) and the rotor current angle (φ.sub.I), and the rotor rotational speed (n.sub.R) resulting from monitoring of the rotor position (Θ.sub.R).

Claims

1. A computer-implemented method for determining a position (Θ.sub.R) and rotational speed (n.sub.R) of a rotor of an electric machine during an active short circuit, wherein the method comprises: determining the short circuit currents (I.sub.U, I.sub.V, I.sub.W) occurring during the short circuit, determining a total current (I.sub.α, I.sub.β) arising from the short circuit currents (I.sub.U, I.sub.V, I.sub.W), determining a stator current angle (ψ.sub.I) of the total current (I.sub.α, I.sub.β) with respect to a stator coordinate system (α, β), determining a rotor current angle (φ.sub.I) of the total current (I.sub.α, I.sub.β) with respect to a direction of flow (d.sub.R) of the rotor by: calculating an absolute-value variable (I) of the total current (I.sub.α, I.sub.β) determining the rotor current angle (φ.sub.I) on the basis of a characteristic dependence, produced for the electric machine, between the absolute-value total current (I) and a rotor current angle (φ.sub.I), wherein the rotor position (Θ.sub.R) corresponds to a sum of the stator current angle (ψ.sub.I) and the rotor current angle (φ.sub.I), and wherein the rotor rotational speed (n.sub.R) is obtained from monitoring the rotor position (Θ.sub.R), and wherein a rotor position smoothed value (Θ.sub.Rg) is determined from smoothing a multiplicity of rotor position values (Θ.sub.R).

2. The method for determining a position (Θ.sub.R) and rotational speed (n.sub.R) of a rotor of an electric machine as claimed in claim 1, wherein the characteristic dependence is determined by relating to one another the rotational-speed-dependent value of absolute-value total current (I) and of the rotor current angle (φ.sub.I).

3. The method for determining a position (Θ.sub.R) and rotational speed (n.sub.R) of a rotor of an electric machine as claimed in claim 1, wherein the method comprises a step in which the determined rotor position (Θ.sub.R) and/or rotor rotational speed (n.sub.R) are/is compared with the sensor information.

4. A rotor state-determining device (10) comprising: a current-determining unit (14) for determining the short circuit currents (I.sub.U, I.sub.V, I.sub.W) which occur during the short circuit, a total current-determining unit (18) for determining a total current (I.sub.α, I.sub.β) which results from the short circuit currents (I.sub.U, I.sub.V, I.sub.W), a stator current angle-determining unit (22) for determining a stator current angle (ψ.sub.I) of the total current (I.sub.α, I.sub.β) with respect to a stator coordinate system (α, β), a rotor current angle-determining device (26) for determining a rotor current angle (φ.sub.I) of the total current (I.sub.α, I.sub.β) with respect to a direction of flow (d.sub.R) 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 (I.sub.α, I.sub.β), and a current angle-correlation unit (34) for determining the rotor current angle (φ.sub.I) which is correlated with the absolute-value total current (I), a rotor position-determining unit (38) for determining a rotor position (Θ.sub.R), a rotor rotational speed-determining device (42) for determining a rotor rotational speed (n.sub.R), and a smoothing unit for determining a rotor position smoothed value (Θ.sub.Rg) determined from smoothing a multiplicity of rotor position values (Θ.sub.R).

5. The rotor state-determining device (10) as claimed in claim 4, wherein the electric machine is a permanent magnetic synchronous machine, an electrically excited synchronous machine or a synchronous reluctance machine.

6. The rotor state-determining device (10) as claimed in claim 4, wherein the electric machine has three phases.

7. A non-transitory, computer-readable medium containing instructions that when executed by a computer in a control unit (14, 18, 22, 26, 38, 42) of a rotor state-determining device (10) cause the computer to determine the short circuit currents (I.sub.U, I.sub.V, I.sub.W) occurring during the short circuit, determine a total current (I.sub.α, I.sub.β) arising from the short circuit currents (I.sub.U, I.sub.V, I.sub.W), determine a stator current angle (ψ.sub.I) of the total current (I.sub.α, I.sub.β) with respect to a stator coordinate system (α, β), determine a rotor current angle (φ.sub.I) of the total current (I.sub.α, I.sub.β) with respect to a direction of flow (d.sub.R) of the rotor by: calculate an absolute-value variable (I) of the total current (I.sub.α, I.sub.β), determine the rotor current angle (φ.sub.I) on the basis of a characteristic dependence, produced for the electric machine, between the absolute-value total current (I) and a rotor current angle (φ.sub.I), wherein the rotor position (Θ.sub.R) corresponds to a sum of the stator current angle (ψ.sub.I) and the rotor current angle (φ.sub.I), and wherein the rotor rotational speed (n.sub.R) is obtained from monitoring the rotor position (Θ.sub.R), and wherein a rotor position smoothed value (Θ.sub.Rg) is determined from smoothing a multiplicity of rotor position values (Θ.sub.R).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are illustrated in the drawing and explained in more detail in the following description. In the drawing:

(2) FIG. 1 shows an exemplary embodiment of a method and of a rotor state-determining device for determining a position and rotational speed of a rotor of an electric machine,

(3) FIG. 2 shows a graphic illustration of a position determination process of a rotor with respect to a stator using the example of a three-phase electric machine,

(4) FIG. 3 shows diagrams relating to the derivation of a characteristic dependence between the absolute-value total current and a rotor current angle, and

(5) FIG. 4 shows a diagram of the characteristic dependence between the absolute-value total current and a rotor current angle.

DETAILED DESCRIPTION

(6) FIG. 1 shows an exemplary embodiment of a method and an exemplary embodiment of a rotor state-determining device 10 for determining a position OR and rotational speed n.sub.R of a rotor (not shown) of an electric machine (not shown). For this purpose, the short circuit currents I.sub.U, I.sub.V, I.sub.W occurring during an active short circuit are determined in a current-determining unit 14, using the example of a three-phase electric machine. The resulting short circuit currents I.sub.U, I.sub.V, I.sub.W are illustrated in FIG. 2. A total current I.sub.α, I.sub.β arising from the short circuit currents I.sub.U, I.sub.V, I.sub.W is then determined in a total current-determining unit 18 of the rotor state-determining device 10. A graphic determination of the total current I.sub.α, I.sub.β from the short circuit currents I.sub.U, I.sub.V, I.sub.W which are offset by 120° for a three-phase motor is illustrated in FIG. 2.

(7) A stator current angle-determining unit 22 determines an angle, denoted as a stator current angle ψ.sub.I and shown in FIG. 2, of the total current I.sub.α, I.sub.β with respect to a stator coordinate system α, β. A direction of flow of the total current I.sub.α, I.sub.β with respect to the stator coordinate system α, β is indicated by means of the stator current angle ψ.sub.I. The rotor state-determining device 10 additionally comprises a rotor current angle-determining device 26 which comprises a calculation unit 30 in which an absolute-value variable I of the total current I.sub.α, I.sub.β is calculated.

(8) Moreover, the rotor current angle-determining device 26 comprises a current angle-correlation unit 34 which determines a rotor current angle φ.sub.I on the basis of a characteristic dependence, produced for the electric machine, between the absolute-value total current I determined by the calculation unit 30 and a rotor current angle φ.sub.I.

(9) As shown in FIG. 2, the rotor current angle φ.sub.I indicates the angle between the total current I.sub.α, I.sub.β and the direction of flow d.sub.R of the rotor. The rotor state-determining device 10 additionally comprises a rotor position-determining unit 38 which calculates the rotor position Θ.sub.R from a sum of the stator current angle ψ.sub.I and rotor current angle φ.sub.I. The rotor position Θ.sub.R corresponds, as shown in FIG. 2, to the angle between the direction of flow d.sub.R of the rotor with respect to the stator. The rotor rotational speed n.sub.R is determined by means of a rotor rotational speed-determining device 42, by monitoring the rotor position Θ.sub.R.

(10) A rotor position smoothed value Θ.sub.Rg and rotor rotational speed smoothed value n.sub.Rg are calculated from a multiplicity of rotor position values Θ.sub.R and rotor rotational speed values n.sub.R in a smoothing unit 46. Consequently, inaccuracies as a result of large deviations in individual values can be minimized.

(11) FIG. 3 shows diagrams relating to the derivation of a characteristic dependence between the absolute-value total current I and a rotor current angle φ.sub.I. For this purpose, the absolute-value total current I determined from the total current I.sub.α, I.sub.β and the rotor current angle φ.sub.I have been respectively determined for an electric machine as a function of the machine rotational speed n. These rotational-speed-dependent values which are determined in the process are different for each electric machine and characterize said machine.

(12) The absolute-value total current I and the rotor current angle (pi can be related to one another by means of the same machine rotational speed values n without a rotational speed being known. Such a relationship between the two values is shown in FIG. 4. In this figure, the characteristic dependence between the absolute-value total current I and the rotor current angle φ.sub.I is shown. By means of this diagram, the current angle-correlation unit 34 determines, on the basis of the absolute-value total current I, the rotor current angle φ.sub.I associated therewith.