Determination of an interrupted motor phase of an electric motor

Abstract

A method for determining an interrupted motor phase of an electric motor having at least three windings by means of a control unit is disclosed, wherein voltages induced in the windings are determined on outer conductors of the electric motor by means of at least one measuring unit, wherein the measuring unit is connected to at least one outer conductor of the electric motor via at least one resistor, the induced voltages of the outer conductors of the electric motor are compared with one another, and an interrupted motor phase is registered if the induced voltage differs or if a frequency of the induced voltage differs. A control unit, a computer program and a machine-readable storage medium are also disclosed.

Claims

1. A method for determining an interrupted motor phase of an electric motor (2) having at least three windings (6) by a control unit (4), the method comprising: determining voltages induced in the windings (6) on outer conductors (U, V, W) of the electric motor (2) by at least one measuring unit (14), wherein the measuring unit (14) is connected to at least one outer conductor (U, V, W) of the electric motor (2) via at least one resistor (R), comparing induced voltages of the outer conductors (U, V, W) of the electric motor (2) with one another, and registering an interrupted motor phase when the induced voltage differs or when a frequency of the induced voltage differs.

2. The method according to claim 1, wherein the electric motor (2) is at least temporarily deactivated or is operated with a reduced current if an interrupted motor phase (U, V, W) is registered.

3. The method according to claim 1, wherein the control unit (4) is in the form of at least one BEMF comparator (14) or in the form of an electric motor controller with at least one BEMF comparator (14), wherein the induced voltage is measured in the form of a signal from the BEMF comparator (14) and the determined signals of the outer conductors (U, V, W) are compared with one another.

4. The method according to claim 1, wherein an interrupted motor phase (U, V, W) is registered if the frequency of the induced voltage is at least doubled in comparison with a reference frequency on at least one outer conductor (U, V, W).

5. The method according to claim 1, wherein an interrupted motor phase (U, V, W) is registered if the frequency of the induced voltage differs from the reference frequency on at least one outer conductor (U, V, W).

6. The method according to claim 1, wherein an interrupted motor phase (U, V, W) is registered if no induced voltage can be measured on at least one outer conductor U, V, W).

7. The method according to claim 1, wherein the electric motor (2) is an electric motor (2) of an engine cooling system.

8. A control unit (4), wherein the control unit (4) is configured to carry out the method according to claim 1.

9. The control unit according to claim 8, wherein the control unit (4) is a comparator (14) or a measuring unit of an electric motor controller.

10. The control unit according to claim 8, wherein the control unit (4) is a comparator (14) or a measuring unit of a pulse width modulator.

11. A non-transitory machine-readable storage medium (16) having a computer program comprising instructions which, when the computer program is executed by a computer or a control unit (2), cause the latter to carry out a method (1) according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred exemplary embodiments of the invention are explained in more detail below on the basis of highly simplified schematic illustrations, in which:

(2) FIG. 1 shows a schematic circuit diagram of an arrangement having an electric motor and a connected control unit according to one embodiment,

(3) FIG. 2 shows a schematic graph with a detected edge change of the comparator within a measuring window,

(4) FIG. 3 shows a schematic graph with a detected edge change of the comparator within a measuring window in the event of a fault D1,

(5) FIG. 4 shows a schematic graph with a detected edge change of the comparator within a measuring window in the event of an alternative fault D1, and

(6) FIG. 5 shows a schematic graph with a detected edge change of the comparator within a measuring window in the event of a fault D2.

DETAILED DESCRIPTION

(7) FIG. 1 illustrates a schematic circuit diagram of an arrangement 1 having an electric motor 2 and a connected control unit 4 according to one embodiment.

(8) In particular, the circuit diagram is used to illustrate a method for determining an interrupted motor phase U, V, W of the electric motor 2 having three windings 6 by means of the control unit 4.

(9) An equivalent circuit diagram for the electric motor 2 is illustrated. Each winding 6 can be described here as a combination of a resistor 8 and an inductance 10. The respective voltage sources 12 (BEMF) in the windings 6 are likewise illustrated in the form of a sinusoidal profile for the sake of completeness.

(10) The outer conductors U, V, W or the motor phases are not represented in the control unit 4 by circuit breakers. The control unit 4 is implemented at least once and electrically connects the respective outer conductors U, V, W to the comparator 14 via connection points SH1, SH2, SH3. One control unit 4 is illustrated for the sake of simplicity. The induced voltages on the outer conductors U, V, W are measured and are compared with one another. In particular, in the comparator 14 illustrated, the induced voltages of the outer conductors V and W are added to one another and are compared with a doubly induced voltage of the outer conductor U. The voltages are added or doubled by means of the resistors R which are used and are identical.

(11) The control unit 4 has three comparators 14 which compare the respective phases U, V, W with one another in an alternating sequence. In particular, the following comparisons can be carried out: U+V with 2*W V+W with 2*U U+W with 2*V

(12) In this case, the voltages induced in the outer conductors U, V, W, in particular, can be measured and compared with one another. The resistors R are used to measure the induced voltages.

(13) An interrupted motor phase U, V, W is determined if the induced voltage differs or if a frequency of the induced voltage differs.

(14) D1 and D2 show, by way of example, possible interruptions of the motor phases U, V, W.

(15) The control unit 4 may be in the form of a microcontroller, for example, which has a machine-readable storage medium 16 and is programmable.

(16) FIG. 2 illustrates, in a schematic graph, detected edge changes of the comparator 14 within a measuring window during regular operation of the electric motor 2. All comparators 14 have virtually identical values and, in particular, identical frequencies of the determined induced voltages.

(17) For a speed measurement, the pulses are counted four times in time slices of 100 ms each. The four levels shown in FIGS. 2 to 5 are each exemplary excerpts of a plurality of speed measurements which are strung together.

(18) A speed measurement therefore consists of four exemplary levels here which have been determined by the control unit 4 or the comparators 14.

(19) So that the functionality of the electric motor 2 is ensured, the pulses of the respective determined voltages U, V, W within a level must match one another. This is the case in FIG. 2, with the result that the electric motor 2 operates without faults.

(20) FIG. 3 and FIG. 4 show pulse profiles of the speed determination in the event of a fault D1. In this case, two different scenarios may occur during the fault D1.

(21) In a first scenario, if a phase V is disconnected during a start-up of the electric motor 2, the voltage or measured pulses can be omitted since no voltage can be induced on account of the interruption. Twice the voltage of the phase V is then induced. This is illustrated in FIG. 3.

(22) In the second scenario which is illustrated by FIG. 4, no voltage is determined in the motor phase W or no voltage is induced in the phase W over the entire measuring interval.

(23) FIG. 5 shows a schematic graph with a detected edge change of the comparator within a measuring window in the event of a fault D2. In the event of the fault D2, the motor phase V is completely decoupled from the corresponding winding 6. In this case, a measurement result which is comparable to FIG. 3 is produced, in which no voltage can initially be determined and the pulses measured by the comparator 14 are then determined at twice the frequency.

(24) Three comparators 14 with resistance circuitry, as illustrated by way of example in FIGS. 1 to 4 for one phase, are preferably needed to detect an interrupted motor phase. An interruption can be detected if the pulses or levels between the three measured phases differ from one another.