Method for determining a coil temperature of an electric machine

Abstract

A method for determining an actual temperature of a coil of an electric machine, includes detecting a voltage in a no-load state of the electric machine; detecting a current strength in an induced short circuit state of the electric machine; calculating an actual stator coil resistance as a function of the voltage detected during the no-load state and the current strength detected during the active short circuit state; and calculating the actual temperature of the coil of the electric machine as a function of the actual stator coil resistance.

Claims

1. A method for determining a temperature of a stator coil of an electric machine, comprising: measuring in a no-load state of the electric machine an open-circuit voltage across the stator coil of the electric machine; determining from the measured open-circuit voltage a magnetic flux through the stator coil; shorting the stator coil of the electric machine to produce an induced short circuit state and measuring in the induced short circuit state a short-circuit current strength; calculating a stator coil resistance as a function of the magnetic flux determined during the no-load state and the short-circuit current strength measured during the induced short circuit state; and calculating the temperature of the stator coil of the electric machine as a function of the stator coil resistance.

2. The method of claim 1, further comprising switching the electric machine into the no-load state for determining the voltage and subsequently switching the electric machine into the induced short circuit state for determining the induced current.

3. The method of claim 2, further comprising driving a vehicle with the electric machine and switching the electric machine into the no-load state and/or the short circuit state during coasting mode of the vehicle.

4. The method of claim 3, wherein the vehicle is a hybrid vehicle comprising an internal combustion engine, and wherein the method further comprises driving the vehicle with the internal combustion engine when switching into the no-load state and/or the induced short circuit state.

5. The method of claim 1, wherein the temperature of the electric machine is calculated using a model.

6. A vehicle comprising a control device configured to determine a temperature of a stator coil of an electric machine, said control device being configured to block semiconductors of a power electronics of the electric machine and measure in a no-load state of the electric machine an open-circuit voltage across the stator coil of the electric machine, to determine from the measured open-circuit voltage a magnetic flux through the stator coil, to switch the electric machine into an induced short circuit state and measure in the induced short circuit state a short-circuit current strength, to calculate a stator coil resistance as a function of the magnetic flux determined during the no-load state and the short-circuit current strength measured during the induced short circuit state, and to calculate the temperature of the coil of the electric machine as a function of the stator coil resistance.

7. The vehicle of claim 6, further comprising at least one sensor for detecting the open-circuit voltage and/or the short-circuit current strength.

8. The vehicle according to one of the claim 6, wherein the electric machine is a three-phase electric machine.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

(2) FIG. 1 shows a schematic representation of a possible configuration of the method according to the invention in a vehicle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(3) Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

(4) FIG. 1 shows a vehicle 1 including an electric machine 3 with a stator coil 6, an internal combustion engine 4, and a control device 5. In order to determine a temperature of the electric machine 3, the electric machine 3 is first switched into a state no-load by the control device 5 by blocking semiconductors of a power electronics 7 of the electric machine 3, whereupon the control device detects a voltage induced in the state no-load and thereafter switches the electric machine into a state active short circuit. While the electric machine 3 is switched in the state active short circuit the control device 5 detects by way of sensors 8 an induced short circuit current, i.e., an induced current strength and via the detected voltage and the detected short circuit current calculates the actual temperature of the electric machine 3.

(5) For this a magnetic flux is calculated via a voltage measured at a defined rotational speed for example in the freewheel of the electric machine. By means of the magnetic flux an actual stator coil resistance R.sub.S can be concluded via formula (3) at known current strength. Because the stator coil resistance. R.sub.S changes in dependence on an actual temperature the actual temperature of the electric machine or the stator can be concluded via the stator coil resistance R.sub.S via formula (4).

(6) While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

(7) What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: