Method for identifying a fault in a rotor of an electric motor and controller

Abstract

A method for operating a separately excited electric motor, which includes a rotor and a stator, includes the following: determining an electrical characteristic variable of the rotor and an electrical characteristic variable of the stator, calculating an initial setpoint voltage value for the stator based on a setpoint current value, a measured current value, and the determined electrical characteristic variables of the rotor and the stator, checking, based on the calculated initial setpoint voltage value, whether there is an electrical fault, in particular a shorted coil, at the rotor, and providing a fault message and/or disconnecting the electric motor if a fault has been identified.

Claims

1. A method for identifying a fault in a rotor of an electric motor comprising a stator, the method comprising: determining a characteristic variable of the rotor and an electrical characteristic variable of the stator, measuring a current value of the electric motor, calculating an initial setpoint voltage value for the stator based on a setpoint current value, the measured current value, the determined characteristic variable of the rotor, and the determined electrical characteristic variable of the stator, checking, based on a calculated initial setpoint voltage value, whether there is a fault at the rotor, and operating the electric motor based on the initial setpoint voltage value by way of the controller if no fault has been identified, or at least one of: providing a fault message by way of the controller or disconnecting the electric motor by way of the controller if the fault has been identified.

2. The method according to claim 1, wherein the fault is a shorted coil.

3. The method according to claim 2, wherein the controller identifies the fault based on an increased voltage control value compared with fault-free operation of the electric motor.

4. The method according to claim 1, wherein the controller verifies or falsifies a presence of the fault by changing the initial setpoint voltage value.

5. The method according to claim 1, wherein the controller determines in a rotor-fixed coordinate system two setpoint voltage values for the stator and, based on an increased voltage control value for one of the two setpoint voltage values, verifies the fault.

6. The method according to claim 5, wherein the controller verifies the presence of the fault of the rotor if, by changing the setpoint voltage values, one of the two voltage control values still has an increased value and falsifies the presence of the fault if, by changing the setpoint voltage values, both voltage control values have an increased value.

7. The method according to claim 4, wherein the controller at least one of provides the fault message or disconnects the electric motor only upon a verified fault.

8. The method according to claim 7, wherein the controller operates the electric motor using the calculated setpoint value voltage if the identified fault has been falsified by way of the controller.

9. The method according to claim 1, wherein the controller determines at least one of an inductance or a resistance as the characteristic variable of the rotor and the electrical characteristic variable of the stator.

10. The method according to claim 1, wherein the electric motor is a separately excited three-phase machine which is controlled by the controller.

11. The method according to claim 10, wherein the electric motor is a separately excited three-phase synchronous machine.

12. The method according to claim 1, wherein the controller additionally determines the setpoint voltage value based on at least one of a torque demand or a measured angular velocity of the rotor.

13. A controller for an electric motor, wherein the controller is configured to perform the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic side view of an electric motor and a controller according to embodiments of the invention.

(2) FIG. 2 shows a schematic block diagram of a method according to embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) FIG. 1 shows an electric motor 10 and a controller 12 connected electronically to the electric motor 10.

(4) For example, the electric motor 10 and the controller 12 are provided in a vehicle, in particular a motor vehicle.

(5) In this case, the electric motor 10 is designed as a separately excited three-phase synchronous machine, wherein the electric motor 10 comprises a stator 14 and a rotor 16.

(6) The stator 14 surrounds the rotor 16 and, in the embodiment of FIG. 1, has three electromagnets 20, for example 3 coils. Another number of electromagnets 20 is of course also conceivable.

(7) The three electromagnets 20 are arranged offset from one another at an angle of 120°, that is to say at equal angular spacings from one another, and each generate a magnetic field if a voltage with a corresponding voltage value U.sub.S is applied to the respective electromagnet 20. In this case, a current with a current value I.sub.S flows through the electromagnets 20.

(8) The rotor 16 is arranged so as to be able to rotate about an axis of rotation 22. The rotor 16 can comprise an electromagnet 24, for example a coil, through which current flows and which interacts with the electromagnets 20 of the stator 14. In FIG. 1, the electromagnet 24 is indicated by coil windings.

(9) The controller 12 is connected electronically to the electromagnets 20, 24 of the stator 14 and the rotor 16 and designed to apply a corresponding voltage value U.sub.S, U.sub.R in each case to the electromagnets 20, 24 and to determine from the electromagnets 20, 24 in each case a resistance R.sub.S, R.sub.R, an inductance L.sub.S, L.sub.R and a current value I.sub.S, I.sub.R, which flows through the electromagnets 20, 24.

(10) If the electromagnets 20 of the stator 14 generate a magnetic rotating field and a corresponding current flows through the electromagnet 24 of the rotor 16, the rotor 16 rotates about the axis of rotation 22 at an angular velocity ω. More precisely, the controller 12 uses a method to control the energization of the electromagnets 20, 24 accordingly. This method is schematically shown in the block diagram of FIG. 2.

(11) In a first method step (S1), the controller 12 determines an electrical characteristic variable of the stator 14 and an electrical characteristic variable of the rotor 16.

(12) For example, the inductances L.sub.S and the resistances R.sub.S of the electromagnets 20 of the stator 14 and accordingly also the resistance R.sub.R and the inductance L.sub.R of the electromagnet 24 (coil) of the rotor 16, which have been (previously) measured by at least one sensor, are provided to the controller 12.

(13) It is also conceivable for the inductances L.sub.S, L.sub.R and the resistances R.sub.S, R.sub.R to also be stored in a data memory, such as a read-only memory or a random-access memory of the controller 12 and for the controller 12 to read out the corresponding values from the data memory.

(14) In this case, the resistances R.sub.S and inductances L.sub.S of each electromagnet 20 of the stator 14 do not necessarily have to be identical. For the sake of simplicity, the resistances R.sub.S and inductances L.sub.S of the stator 14 are characterized by only one reference sign.

(15) Subsequently (method step S2), the current values I.sub.S of the stator 14 and the current value I.sub.R of the rotor 16 as well as the angular velocity ω of the rotor 16 are measured, for example by way of a Hall sensor. The corresponding values are provided to the controller 12.

(16) Here, too, it is pointed out that the maximum values of the current values I.sub.S that are measured at each electromagnet 20 do not necessarily have to be identical.

(17) In particular, the profile of the current values I.sub.S applied to the corresponding electromagnet 20 is shifted in each case by 120° with respect to another, that is to say correspondingly phase-shifted.

(18) In a next method step (S3), the controller 12 receives a torque demand D and transforms the variables received and determined to a rotor-fixed coordinate system with the axes d and q by way of a Park transformation.

(19) Subsequently, in step S4, the controller 12 determines an initial setpoint voltage value U.sub.S for the stator 14, that is to say the electromagnets 20, based on the electrical characteristic variables R.sub.S, L.sub.S of the stator 14, the electrical characteristic variables R.sub.R, L.sub.R of the rotor 16, setpoint current values I.sub.S*, I.sub.R* of the stator 14 and the rotor 16, which result from the torque demand D, and the angular velocity ω of the rotor 16.

(20) For this purpose, the controller 12 uses a mathematical model, which comprises the following equations:

(21) $\begin{array}{cc}{U}_d=R_1{I}_d^{*}+\frac{d}{\mathrm{dt}}{\psi }_d-\omega {\psi }_q,& \left(1\right)\\ U_q=R_1{I}_q^{*}+\frac{d}{\mathrm{dt}}{\psi }_q+\omega {\psi }_d,\mathrm{and}& \left(2\right)\\ U_R=R_R{I}_R^{*}+\frac{d}{\mathrm{dt}}{\psi }_R.& \left(3\right)\end{array}$

(22) In the equations, U.sub.d, U.sub.q are the initial setpoint voltage values for the stator 14 and I.sub.q*, I.sub.d* the setpoint current values of the stator 14 in the d-q coordinate system, I.sub.R* the setpoint voltage value of the rotor 16, R.sub.1 the combined resistance of the electromagnets 20 of the stator 14 and ψ.sub.q, ψ.sub.q, ψ.sub.R are the magnetic linked fluxes, which are determined by the following equations:
ψ.sub.d=L.sub.dRI.sub.R*+L.sub.dI.sub.d*,  (4)
ψ.sub.q=L.sub.qI.sub.q*, and  (5)
ψ.sub.R=L.sub.RdI.sub.d*+L.sub.RI.sub.R*.  (6)

(23) In this case, L.sub.d, L.sub.q are the inductances of the stator 14 that are transformed to the d-q coordinate system and the inductances L.sub.dR, L.sub.Rd are the coupling inductances between the electromagnets 20 of the stator 14 and the electromagnet 24 of the rotor 16.

(24) In a next method step, the controller 12 controls the voltages U.sub.S applied to the stator 14 using field-oriented control.

(25) For this purpose, the controller 12 uses the measured current values I.sub.S, I.sub.R of the stator 14 and the rotor 16 and accordingly corrects the initial setpoint voltage values U.sub.S at the electromagnets 20 of the stator 14.

(26) In this case, the derivations of the linked fluxes are set to be equal to 0 and accordingly produce the following control equations for the controller 12:
U.sub.d=U.sub.d,R+R.sub.1I.sub.d−ωψ.sub.q,  (7)
U.sub.q=U.sub.q,R+R.sub.1I.sub.q+ωψ.sub.d, and  (8)
U.sub.R=U.sub.R,R+R.sub.RI.sub.R.  (9)

(27) The variables U.sub.d, U.sub.q and U.sub.R have been determined in this case by way of the mathematical model and the controller 12 adapts the setpoint voltage values U.sub.d, U.sub.q of the stator 14 by correspondingly adapting the voltage control values U.sub.d,R and U.sub.q,R. Furthermore, the setpoint voltage value U.sub.R of the rotor 16 is adapted by adapting the voltage control value U.sub.R,R.

(28) Fault-free operation of the electric motor 10 results in U.sub.d,R≈U.sub.R,R≈U.sub.q,R≈0. The controller 12 thus has to intervene only a little in the fault-free operation of the electric motor 10.

(29) Based on this control, the controller 12 checks in step S6 whether there is an electrical fault F at the rotor 16. In this case, the controller 12 identifies the presence of the electrical fault F based on an increased voltage control value U.sub.q,R. The controller 12 thus has to intervene to a great extent in order to achieve the setpoint voltage value U.sub.S, that is to say the voltage values U.sub.d and U.sub.q of the mathematical model.

(30) Depending on the result of this check, the controller 12 behaves differently (this is shown by the two arrows in the block diagram of FIG. 2, which extend away from the box of step S6).

(31) If there is no electrical fault KF, the controller 12 operates the electric motor 10 based on the calculated initial setpoint voltage value U.sub.S (step S7). This is illustrated in FIG. 2 by a corresponding arrow to the electric motor 10.

(32) In the other case (the controller 12 identifies an electrical fault F), the controller 12 checks whether there is actually an electrical fault (step S8).

(33) In other words, the controller 12 verifies or falsifies the presence of the electrical fault F.

(34) For this purpose, the controller 12 varies the voltage values U.sub.S applied to the stator 14.

(35) The controller 12 thus varies the current values I.sub.S applied to the stator 14. For example, the controller 12 controls the current values I.sub.S of the stator 14 in such a way that they are equal to 0, and applies a current value I.sub.R not equal to zero to the rotor 16.

(36) If the controller 12 then still has to provide an increased voltage control value U.sub.q,R, there is a verified electrical fault VF and the controller 12 provides in step S9 a corresponding fault message M and/or disconnects the electric motor 10.

(37) If the controller 12 has to control both voltage control values U.sub.q,R and U.sub.d,R to a great extent, there is a fault in the position of the rotor 16. The controller 12 therefore identifies a falsified electrical fault FF. In this case, the controller 12 corrects the position of the rotor 16 and then operates the electric motor 10 using the initial setpoint voltage value U.sub.S.

(38) Simple identification of an electrical fault F at the rotor 16 is thus made possible by the controller 12 and the described method. In this case, the presence of an electrical fault F has an impact on the electromagnets 20 of the stator 14 by way of the electromagnetic interaction between the rotor 16 and the stator 14.

(39) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.