Method for detecting an error in a generator unit

Abstract

The invention relates to a method for detecting an error in a generator unit which has an electric machine (100) with a rotor winding (110), a stator winding (120), and a rectifier (130) connected thereto, via which the electric machine (100) is connected to an onboard electrical system (150) of a motor vehicle, wherein a voltage of the onboard electrical system (150) is controlled to a target value via an excitation current (I.sub.E) through the rotor winding (110) of the electric machine (100), and a curve of a phase voltage (U.sub.y) of the stator winding (120) is monitored, wherein an error in the generator unit is inferred when a change of the phase voltage (U.sub.y) is detected and a voltage of the onboard electrical system (150) changing within a threshold value range (S) is detected.

Claims

1. A method for detecting an error in a generator, the generator including an electrical machine with a rotor winding and a stator winding and a rectifier, the method comprising: connecting, via the rectifier, the electrical machine to an on-board electrical network of a motor vehicle, regulating, via an excitation current through the rotor winding of the electrical machine, a voltage of the onboard network to a nominal value, and monitoring, with a computer, a waveform of a phase voltage of the stator winding, wherein an error is assumed to exist in the generator unit if a change in the phase voltage is detected and wherein the error is assumed to exist in the generator unit if a voltage varying within a threshold band of the onboard network is also detected and/or an oscillating progression of the variation in the temporal width of the pulse of the phase voltage is detected, and wherein a magnitude of the oscillation exceeds a threshold, or an increased amplitude of the pulses of the phase voltage is detected.

2. The method as claimed in claim 1, wherein a frequency of the oscillation is proportional to a number of pole pairs and/or a current rotation speed of the electrical machine.

3. The method as claimed in claim 1, wherein the fault comprises a short circuit and/or an interruption in a high-side path between the rectifier and the onboard network, a short circuit and/or an interruption in a low-side path between the rectifier and the onboard network, a short circuit of the stator winding in relation to the onboard network, a break in a wire of the stator winding, a short circuit between wires of the stator winding and/or a short circuit between different phases.

4. The method as claimed in claim 1, wherein a nature of the error is inferred on the basis of the magnitude of the oscillation and/or on the basis of a frequency of the oscillation and/or on the basis of the oscillating progression of the variation in the phase voltage.

5. The method as claimed in claim 1, wherein a countermeasure is carried out if an error in the generator unit is determined.

6. The method as claimed in claim 5, wherein the countermeasure comprises a reduction of the magnitude of the excitation current, in particular by reducing the nominal value of the excitation current, and/or a reduction of a maximum permissible excitation current and/or an error message.

7. The method as claimed in claim 1, wherein the excitation current is regulated to a nominal value.

8. A generator regulator configured to control a generator having an electric machine connected, via a rectifier, to an on-board electrical network of a motor vehicle and having a computer configured to implement a method of controlling the generator, the method comprising: regulating, via an excitation current through a rotor winding of the electrical machine, a voltage of the onboard network to a nominal value, and monitoring, a waveform of a phase voltage of a stator winding of the electrical machine, wherein an error is assumed to exist in the generator if a change in the phase voltage is detected and wherein the error is assumed to exist in the generator unit if a voltage varying within a threshold band of the onboard network is also detected and/or an oscillating progression of the variation in the temporal width of the pulse of the phase voltage is detected, and wherein a magnitude of the oscillation exceeds a threshold, or an increased amplitude of the pulses of the phase voltage is detected.

9. A machine-readable storage medium having a computer program that when implemented by a computer causes the computer to implement a method of controlling a generator having an electric machine connected, via a rectifier, to an on-board electrical network of a motor vehicle, the method comprising: regulating, via an excitation current through a rotor winding of the electrical machine, a voltage of the onboard network to a nominal value, and monitoring, a waveform of a phase voltage of a stator winding of the electrical machine, wherein an error is assumed to exist in the generator if a change in the phase voltage is detected and wherein the error is assumed to exist in the generator unit if a voltage varying within a threshold band of the onboard network is also detected and/or an oscillating progression of the variation in the temporal width of the pulse of the phase voltage is detected, and wherein a magnitude of the oscillation exceeds a threshold, or an increased amplitude of the pulses of the phase voltage is detected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic diagram of a generator unit with an electric machine, rectifier and generator regulator, in which a method according to the invention can be implemented;

(2) FIGS. 2a to 2c show the generator unit of FIG. 1 with different errors in the rectifier;

(3) FIGS. 3a to 3c show diagrams of voltage and current waveforms for the errors shown in FIGS. 2a to 2c; and

(4) FIG. 4 shows a flowchart for a method for detecting a fault in the generator.

DETAILED DESCRIPTION

(5) FIG. 1 shows a schematic diagram of a generator unit having an electrical machine 100 with a rectifier 130 and a processing unit 140 designed as a generator regulator, in which a method according to the invention can be implemented. The electrical machine 100 has a rotor or excitation winding 110 and a stator winding 120, and in this case is used as a generator for supplying power to an on-board electrical network 150 of a motor vehicle.

(6) The electric machine 100 and therefore its stator winding 120 is in this case designed with five phases U, V, W, X and Z. Each of the five phases is linked via an associated diode 131 of the rectifier 130 to a positive side, or high-side B+ of the onboard network 150 and via an associated diode 132 to a negative side, or low-side B of the onboard network 150. It goes without saying that the number five of the phases in the present case is only exemplary and that a method according to the invention can also be implemented with a different phase number, for example 3, 6, 7 or more. It is also possible to use suitable semiconductor switches instead of the diodes.

(7) The generator regulator 140 supplies the rotor winding 110 with an excitation current I.sub.E. Furthermore, the generator regulator 140 has inputs for detecting the on-board electrical network voltage with B+ and B, as well as a phase voltage, which is in the present case is the phase Y, with voltage U.sub.Y. An output current delivered by the electrical machine 100 is designated with I.sub.G.

(8) In FIGS. 2a to 2c, respectively, the arrangement shown in FIG. 1 is shown, each with a specific error in the rectifier 130.

(9) FIG. 2a shows an example of a short-circuit in the high-side path, in the present case in the phase U. This can occur, for example, in the event of a short-circuit of the associated diode 131.

(10) FIG. 2b shows an example of a short-circuit in the low-side path, in the present case in the phase U. This can occur, for example, in the event of a short-circuit of the associated diode 132.

(11) FIG. 2c shows an example of an interruption in a low-side path, in the present case in the phase U. Such an interruption occurs, for example, if the associated diode 132 is disconnected on one side of the diode, or, as shown in the figure, on both sides of the diode, or if the diode is destroyed, for example. An interruption in a high-side path would accordingly occur, for example, in the case of a disconnection or destruction of a diode 131.

(12) FIGS. 3a to 3c show waveforms of the generator voltage U+, the generator current I.sub.G, the phase voltage U.sub.Y of the phase Y and of the excitation current I.sub.E over time t, respectively. Before time t.sub.0 a normal operation of the arrangement prevails and at time t.sub.0 a fault occurs in the generator unit. The curves in FIGS. 3a to 3c are associated with waveforms, which correspond to errors as shown in FIGS. 2a to 2c. It should be noted here that the scaling of the individual diagrams for both current and voltage as well as for time does not always match, but this is not relevant to the present invention.

(13) In FIG. 3a it is apparent that a short circuit in a high-side path becomes noticeable in the generator voltage just a short time after the error has occurred. The generator voltage after time t.sub.0 thus shows a typical waveform within a threshold band S and has a substantially constant mean temporal progression. The waveform within the threshold bands S, however, is not absolutely necessary for error detection, but it can be used as an additional criterion. The generator current decreases and the phase voltage U.sub.Y varies in such a way that the temporal width 2 of the pulses of the phase voltage U.sub.Y after the error differs significantly from the temporal width 1 of the pulses of the phase voltage U.sub.Y before the error. On closer examination, the temporal variation in the width of the phase voltage U.sub.Y also has a temporally oscillating progression compared to the waveform without error. The frequency f of the oscillation of the width of the phase voltage U.sub.Y here corresponds to:
f=n.Math.PPZ/60,

(14) where n is the rotation speed of the generator in 1/min and PPZ is the number of pole pairs of the generator.

(15) In FIG. 3b it is apparent that a short circuit in a low-side path is noticeable in the generator voltage just a short time after the error has occurred, and that the generator current decreases. The generator voltage after time t.sub.0 thus also shows a typical waveform within a threshold band S and has a substantially constant mean temporal progression. The waveform within the threshold bands S, however, is not absolutely necessary for error detection, but it can be used as an additional criterion. In the phase voltage U.sub.Y, as also in the short-circuit in the high-side path (FIG. 3a), a significant variation in the temporal width 2 of the pulses of the phase voltage U.sub.Y is apparent following the error, compared to the temporal width 1 of the pulses of the phase voltage U.sub.Y before the error. On closer examination, the temporal variation in the width of the phase voltage U.sub.Y also has a temporally oscillating waveform in comparison to the waveform without error, wherein the frequency f of the oscillation of the width of the phase voltage U.sub.Y follows the same relationships as shown in FIG. 3a.

(16) In FIG. 3c it is apparent that an interruption in a low-side path leads to slight fluctuations in the generator voltage, which typically varies within a threshold band S and has an essentially constant mean temporal progression. The waveform within the threshold bands S, however, is not absolutely necessary for error detection, but it can be used as an additional criterion. The generator current follows an oscillation, in which the value of the current on reaching the respective disconnected low-side path in each case tends to zero. The phase voltage U.sub.Y has a higher amplitude than before the error, and a significant variation in the temporal width 2 of the pulses of the phase voltage U.sub.Y is also apparent following the error, compared to the temporal width 1 of the pulses of the phase voltage U.sub.Y before the error. On closer examination, the temporal variation in the width of the phase voltage U.sub.Y also has a temporally oscillating waveform in comparison to the waveform without error, wherein the frequency f of the oscillation of the width of the phase voltage U.sub.Y follows the same relationships as shown in FIG. 3a.

(17) In summary, it is evident that on the basis of the phase voltage in conjunction with a substantially constant generator voltage, all the errors referred to in the rectifier and/or the machine can be detected. Since both the phase voltage and the generator voltage can already be detected due to the regulation in the generator regulator, the method can be implemented very easily without additional constructive effort.

(18) FIG. 4 shows an example flow chart for a method for detecting an error in a generator unit. In step 200, the temporal width of the pulses of the phase voltage U.sub.Y is determined and, if appropriate, stored in a memory for further processing. In step 202, the temporal widths of the individual pulses of the phase voltage U.sub.Y are compared with each other in order to determine whether a significant deviation in the temporal pulse widths exceeding a threshold value exists. It can also be checked in 206 and 208 whether the pulse widths are subject to an oscillatory variation.

(19) In the event that 202 evaluates negative and 206 is also negative, there is no error in the system. In the event that 202 evaluates negative and 206 evaluates in the affirmative, in step 214 it can be checked whether the voltage of the onboard electrical network 115 varies within a threshold band S and/or whether it has a substantially constant mean temporal progression. If the outcome of step 214 is negative, the system is in an undefined state 218 and, if necessary, an error message can be output and/or the state can be checked for plausibility by one of the other measured values shown in FIG. 3. If step 214 evaluates in the affirmative, then the generator has a defect 220.

(20) In the event that 202 evaluates in the affirmative and 208 (presence of an oscillatory variation) also evaluates in the affirmative, it can be checked whether the voltage of the onboard electrical network 115 varies within a threshold band S and/or whether it has a substantially constant mean temporal progression 222. In the event that 208 is affirmative and 222 is also affirmative, there is a fault in the generator 220. If step 208 is affirmative and 222 evaluates negative, the system is in an undefined state 224 and, if necessary, an error message can be output, and/or the state can be checked for plausibility by one of the other measured values shown in FIG. 3. The same applies to the case in which 208 evaluates negative.