Method and electronic assembly for determining a temperature of at least one electronic switching element

Abstract

A method determines a temperature of at least one electronic switching element by way of a temperature measuring circuit. A first electronic switching element in an electronic module is first of all turned off and a second electronic switching element in the electronic module is turned on. A voltage measuring unit is then coupled to the electronic module and a voltage drop across the second electronic switching element is measured. A current intensity of a current flowing through the second electronic switching element is also determined and the temperature of the second electronic switching element is determined with the inclusion of the measured voltage drop and the determined current intensity. An electronic assembly for determining a temperature of at least one electronic switching element is also described.

Claims

1. A method for determining a temperature of at least one electronic switching element by a temperature measuring circuit comprising at least one electronic module having a first electronic switching element and a second electronic switching element, wherein the first and second electronic switching elements are configured so as to block a current flow in one direction in a first switching position, the method comprising the steps of: a) turning off the first electronic switching element and turning on the second electronic switching element; b) coupling a voltage measuring unit to the electronic module; c) measuring a voltage drop across the second electronic switching element; d) measuring a current intensity of a current flowing through the second electronic switching element; and e) ascertaining the temperature of the second electronic switching element based on a resistance of the second electrical switching element, wherein the resistance is determined based on the measured voltage drop and the measured current intensity, wherein: the current intensity of the current flowing through the second electronic switching element is measured by way of measurement of a current through a load, and the load is an inductor.

2. The method according to claim 1, further comprising the step of: turning on an electronic switching unit in order to couple the voltage measuring unit to the electronic module, wherein the electronic switching unit is configured so as to block a current flow in one direction in a first switching position.

3. The method according to claim 2, further comprising the step of: driving, via a controller, at least one of the first and second electronic switching elements and/or the electronic switching unit.

4. The method according to claim 2, further comprising the step of: driving, via a controller, both the first and second electronic switching elements and the electronic switching unit.

5. The method according to claim 2, wherein at least the electronic switching unit comprises a field effect transistor.

6. The method according to claim 5, wherein the field effect transistor is a MOSFET.

7. The method according to claim 5, wherein the field effect transistor is an SiC MOSFET.

8. The method according to claim 1, wherein after step d), the voltage measuring unit is decoupled from the electronic module before the second electronic switching element is turned off and the first electronic switching element is turned on.

9. The method according to claim 1, wherein the temperature is ascertained on the basis of a functional relationship or is taken from a table of values.

10. An electronic assembly for determining a temperature of at least one electronic switching element, comprising: at least one electronic module having a first electronic switching element and a second electronic switching element, wherein an electronic switching unit is provided, which is turned off in a first switching position and is turned on in a second switching position, such that a voltage measuring unit is coupled to the electronic module such that the voltage measuring unit measures a voltage drop across the second electronic switching element, a current measuring unit is provided, which is configured to measure the current intensity of a current flowing through the second electronic switching element by way of measurement of a current through a load, wherein the load is an inductor, and a control and evaluation unit is provided, which is designed to process the measured voltage and the measured current intensity in order to determine a resistance of the second electrical switching element, and to determine the temperature of the second electronic switching element based on the resistance of the second electrical switching element.

11. The electronic assembly according to claim 10, wherein the electronic switching unit is coupled to the electronic module via an electrical line, and the electrical line branches off from the electronic module between the first electronic switching element and the second electronic switching element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a circuit diagram of an electronic assembly according to an embodiment of the invention.

(2) FIG. 2 is a graph showing a temporal profile of a drain-source voltage across the second electronic switching element of the electronic assembly in accordance with FIG. 1.

(3) FIG. 3 is a graph showing a family of characteristic curves of the second electronic switching element of the electronic assembly in accordance with FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) The construction of an electronic assembly 10 for determining a temperature of at least one electronic switching element is explained below with reference to FIG. 1.

(5) FIG. 1 shows a circuit diagram of the electronic assembly 10, which has a temperature measuring circuit for the electronic switching element. The electronic assembly 10 comprises an electronic module 12 having a first electronic switching element 14 and a second electronic switching element 16.

(6) The electronic assembly 10 furthermore comprises an electronic switching unit 18, via which a voltage measuring unit 20 is able to be coupled to the electronic module 12.

(7) The electronic switching unit 18 is connected to the electronic module 12 via an electrical line 18L. The electrical line 18L branches off between the first electronic switching element 14 and the second electronic switching element 16.

(8) In the embodiment shown, the electronic switching unit 18 has an electronic switching element 21 configured as a MOSFET, to put it more precisely as a normally off n-channel MOSFET. In particular, an SiC MOSFET is involved.

(9) Moreover, a current measuring unit 22 is provided, which is designed to determine the current intensity of a current through the second electronic switching element 16.

(10) The voltage measuring unit 20 and the current measuring unit 22 can each comprise an analog-to-digital converter, such that the analog input signals are digitized.

(11) Moreover, in the embodiment shown, an inductive component 24, in particular an inductor, is connected in series with the current measuring unit 22.

(12) The electronic switching elements 14, 16 are configured for example as MOSFETs, to put it more precisely as normally off n-channel MOSFETs. In particular, SiC MOSFETs are involved. A drain terminal 14D of the first (high-side) electronic switching element 14 is connected to a positive pole of a DC source 26. In addition, a source terminal 16S of the second (low-side) electronic switching element 16 is connected to a negative pole of the DC source 26.

(13) A control and evaluation unit 28 is additionally provided, which drives the two electronic switching elements 14, 16 and the electronic switching unit 18 via electrical lines (not illustrated more specifically). In addition, via lines (not illustrated here), the control and evaluation unit 28 obtains the measurement results of the voltage measuring unit 20 and the current measuring unit 22 in order correspondingly to evaluate them, as will also be explained below.

(14) Electrical lines and electronic components additionally required for the operation of the electronic module 12 are not shown in FIG. 1 for reasons of clarity.

(15) A method for determining a temperature of at least one electronic switching element by way of the temperature measuring circuit described above is described below with reference to FIGS. 1 to 3.

(16) For determining the temperature of the second electronic switching element 16, firstly the first electronic switching element 14 is turned off and the second electronic switching element 16 is turned on. This is also referred to as step a). Step a) is carried out at a time t.sub.I (see FIG. 2).

(17) After step a), the second electronic switching element 16 is decoupled from the DC source 26. Therefore, a link circuit voltage U.sub.ZK of the DC source 26 is no longer present at the second electronic switching element 16.

(18) The voltage measuring unit 20 is then coupled to the electronic module 12, which is referred to as step b). The coupling is effected by the electronic switching unit 18 being turned on, in particular the switching element 21 thereof.

(19) A voltage drop U.sub.DS between drain and source terminals of the second electronic switching element 16 is then measured by means of the voltage measuring unit 20, which is referred to as step c).

(20) The voltage drop between drain and source terminals of the second electronic switching element 16 is dependent on the temperature of the second electronic switching element 16 since the ohmic resistance thereof is temperature-dependent.

(21) The voltage measuring unit 20 is designed, in particular, to measure the voltage drop U.sub.DS so accurately that differences in the voltage drop U.sub.DS at different temperatures of the second electronic switching element 16 are resolvable.

(22) As can be seen in FIG. 2, the voltage drop U.sub.DS after step a), that is to say at times greater than t.sub.I (see FIG. 2), is significantly less than the link circuit voltage U.sub.ZK of the DC source 26. Differences in the voltage drop U.sub.DS at different temperatures are therefore smaller than the link circuit voltage U.sub.ZK potentially by a plurality of orders of magnitude.

(23) Therefore, in step a), the second electronic switching element 16 is decoupled from the DC voltage source 26 before the voltage measuring unit 20 is coupled to the electronic module 12. The link circuit voltage U.sub.ZK could otherwise damage the voltage measuring unit 20.

(24) The current intensity of a current I.sub.DS flowing through the second electronic switching element 16 is determined by way of the current measuring unit 22, which is reflected as step d). This can be carried out in particular by the measurement of a current that flows through the inductive component 24, in particular proceeds from the latter.

(25) With the inclusion of the measured voltage drop U.sub.DS and the determined current intensity of the current I.sub.DS, the temperature T of the second electronic switching element 16 is then ascertained, in particular by the control and evaluation unit 28, which obtains the measured values of the voltage measuring unit 20 and the current measuring unit 22. This is also referred to as step e).

(26) Step e) is explained in more specific detail below. Firstly, the ohmic resistance R.sub.DS,on of the second electronic switching element 16 in the on state is ascertained in accordance with Ohm's law, that is to say by way of:

(27) $R_{\mathrm{DS},\mathrm{on}}=\frac{U_{\mathrm{DS}}}{I_{\mathrm{DS}}}$

(28) Since the ohmic resistance R.sub.DS,on is temperature-dependent, the temperature T of the second electronic switching element 16 can be ascertained from said ohmic resistance and the determined current intensity I.sub.DS.

(29) If the functional relationship between the temperature T, the ohmic resistance R.sub.DS,on and the determined current intensity I.sub.DS is known, then the temperature of the second electronic switching element 16 can be calculated in accordance with the following formula:
T=f(R.sub.DS,on,I.sub.DS)

(30) In this case, f is a function which assigns a temperature to pairs of values (R.sub.DS,on,I.sub.DS).

(31) Alternatively, the temperature T can be read from a table of values that assigns a temperature to the pairs of values (R.sub.DS,onI.sub.DS).

(32) Analogously to the explanations above, the temperature of the second electronic switching element 16 can also be determined from the ohmic resistance R.sub.DS,on and the measured voltage drop U.sub.DS.

(33) If the functional relationship is known, then the temperature of the second electronic switching element 16 can be calculated in accordance with the following formula:
T=g(R.sub.DS,on,U.sub.DS)

(34) In this case, g is a function that assigns a temperature T to pairs of values (R.sub.DS,on,U.sub.DS).

(35) Alternatively, the temperature T can be read from a table of values that assigns a temperature to the pairs of values (R.sub.DS,onU.sub.DS).

(36) Likewise analogously to the explanations above, the temperature of the second electronic switching element 16 can also be determined directly from the measured voltage drop U.sub.DS and the determined current intensity I.sub.DS.

(37) If the functional relationship is known, the temperature of the second electronic switching element 16 can be calculated in accordance with the following formula:
T=h(U.sub.DS,I.sub.DS)

(38) In this case, h is a function that assigns a temperature T to the pairs of values (U.sub.DS,I.sub.DS).

(39) Alternatively, the temperature T can be read from a table of values that assigns a temperature to the pairs of values (U.sub.DS,I.sub.DS).

(40) The control and evaluation unit 28 can be fashioned in such a way that it automatically carries out the method described above and, in particular, automatically determines the temperature of the second electronic switching element 16.

(41) The method can analogously also be applied for measuring a temperature of the first electronic switching element 14. In this case, a voltage measuring unit 20 is then able to be coupled to the electronic module 12 via an electronic switching unit 18 in such a way that the voltage measuring unit 20 taps off a voltage across the first electronic switching element 14.

(42) The voltage measuring unit 20 is then only coupled to the electronic module 12 if the first electronic switching element 14 is turned on and the second electronic switching element 16 is turned off.

(43) Otherwise, reference is made to the explanations above.

(44) FIG. 3 shows a diagram in which the measured current intensity I.sub.DS is plotted against the measured voltage drop U.sub.DS for three different temperatures, namely for 25 C., 150 C. and 175 C. The temperature dependence of the measured values is evident from the diagram. This makes it clear that the temperature of the electronic switching element can correspondingly be determined by way of the measured values.

(45) 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.