Method for measuring a collector current of a semiconductor switch using a measuring resistor

Abstract

The present invention relates to a method for measuring a collector current (Ic) of a semiconductor switch, comprising a first step for determining a value of the measuring resistor (Rs), a second step for measuring a voltage drop (Us) across the measuring resistor (Rs), which is connected between an emitter terminal (E1) of a measuring semiconductor switch (S1) of the semiconductor switch and an emitter terminal (E2) of a main semiconductor switch (S2) of the semiconductor switch, a third step for determining a measuring current (Is) from a quotient of the voltage drop (Us) across the measuring resistor (Rs) and the value of the measuring resistor (Rs), a fourth step for determining a gate voltage of the measuring semiconductor switch (S1) based on an area-adjusted current value and a transfer function, a fifth step for determining a gate voltage of the main semiconductor switch (S2),by adding an ohmic total voltage drop and an inductive voltage drop between the emitter (E1) of the measuring semiconductor switch (S1) and the emitter (E2) of the main semiconductor switch (S2) to the gate voltage of the measuring semiconductor switch (S2), and a sixth step for determining a collector current (Ic) of the main semiconductor switch based on the determined gate voltage of the main semiconductor switch (S2) and the transfer function.

Description

State of the art

[0001] The present invention relates to a method for measuring a collector current of a semiconductor switch by means of a measuring resistor.

[0002] Power modules are known from the state of the art in which several power semiconductor switches, such as IGBTs, designed as chips are connected in parallel.

[0003] For various reasons, it can be important to obtain information about the distribution of the total current flowing through the power module among the individual chips. For example, there may be cases where a particularly uniform distribution across the respective parallel-connected chips is desired, but there may also be cases where a non-uniform distribution is desired.

[0004] Measuring the current distribution in such a power module is traditionally performed using open power modules that are not packaged in a housing. This makes it possible, for example, to insert a so-called Rogowski coil between the chips to measure the current flowing through each chip independently. Disclosure of the invention

[0005] The method according to the invention for measuring a collector current of a semiconductor switch by means of a measuring resistor offers the particular advantage that this method can be carried out in connection with semiconductor chips and / or semiconductor modules which can be enclosed by a housing, in particular by an injection-molded housing, so that a conventional measurement by means of a Rogowski coil is not possible.

[0006] It should be noted in general that the method steps described below can be carried out at least partially on the basis of an evaluation unit which, for example, executes a computer program which implements the method steps according to the invention.

[0007] In a first step of the method according to the invention, a resistance value of the measuring resistor is determined. This is preferably done based on a four-wire measurement in order to achieve a particularly accurate measurement result. During this step, the measuring resistor is preferably separated from other components (e.g., physically separated or separated by a suitable isolating device such as a switch, in particular a mechanical and / or electromagnetic switch, etc.) so that it can be measured using a suitable measuring arrangement without interference from other components.

[0008] In a second step of the method according to the invention, a voltage drop across the measuring resistor is measured in a state in which the measuring resistor is connected between an emitter terminal of a measuring semiconductor switch of the semiconductor switch and an emitter terminal of a main semiconductor switch of the semiconductor switch, wherein respective collector terminals of the main semiconductor switch and the measuring semiconductor switch and respective gate terminals of the main semiconductor switch and the measuring semiconductor switch are electrically connected to one another and wherein a DC voltage is applied between the collector terminals and the emitter terminals.

[0009] The measuring semiconductor switch and the main semiconductor switch are preferably formed using the same process technology and more preferably on a single substrate, so that they represent, for example, a single chip.

[0010] The main semiconductor switch has a first area that is larger than a second area of ​​the measuring semiconductor switch. Preferably, the first area is substantially larger than the second area, so that only a small current flows through the measuring semiconductor switch, which is connected in parallel with the main semiconductor switch. For example, a ratio of the first area to the second area corresponds to a factor of 1000, without thereby imposing a restriction on such an area ratio.

[0011] In a third step of the method according to the invention, a measuring current is determined from a quotient of the voltage drop across the measuring resistor and the resistance value of the measuring resistor as follows: Is=UsRs where Is represents the measuring current, Us the measured voltage drop and Rs the resistance value of the measuring resistor.

[0012] In a fourth step of the method according to the invention, a gate-emitter voltage of the measuring semiconductor switch is determined based on an area-adjusted current value, which results from a product of the measuring current and a quotient of the first area and the second area, and based on a predefined transfer function of the semiconductor switch, which predefines a relationship between an internal gate-emitter voltage of the semiconductor switch and a collector current of the semiconductor switch. The area-adjusted current value is determined accordingly as follows: Isa=Is×A2A1 where Isa represents the area-adjusted current value, Is the measuring current, A2 the area of ​​the main semiconductor switch and A1 the area of ​​the measuring semiconductor switch.

[0013] The internal gate-emitter voltage on which the transfer function is based preferably represents a voltage free of parasitic influences on the gate-emitter voltage. The transfer function is stored, for example, in the form of representative data in a memory unit that is connected to the evaluation unit via information technology.

[0014] In a fifth step of the method according to the invention, a gate-emitter voltage of the main semiconductor switch is determined by adding to the gate-emitter voltage of the measuring semiconductor switch an ohmic total voltage drop between the emitter of the measuring semiconductor switch and the emitter of the main semiconductor switch and in particular additionally an inductive voltage drop between the emitter of the measuring semiconductor switch and the emitter of the main semiconductor switch.

[0015] The inductive voltage drop ΔU ge,M is preferably calculated as follows: ΔUge,M=M×dIsadt where M is an inductive coupling between wirings of the measuring semiconductor switch and wirings inside and outside the semiconductor switch or a chip and / or a module into which the semiconductor switch is integrated.

[0016] The gate-emitter voltage of the main semiconductor switch U ge,S2 is calculated, for example, as follows: Uge,S2=Uge,S1+ΔUge,R+ΔUge,M where U ge,S1 the internal gate-emitter voltage of the measuring semiconductor switch determined in the fourth step, ΔU ge,R the total ohmic voltage drop between the emitter terminal of the measuring semiconductor switch and the emitter terminal of the main semiconductor switch and ΔU ge,M represents the inductive voltage drop determined as above. A concrete composition of the total ohmic voltage drop ΔU ge,Rwill be explained in more detail below in the course of the description of advantageous embodiments of the present invention.

[0017] Finally, in a sixth step of the method according to the invention, a collector current of the main semiconductor switch is determined based on the determined gate-emitter voltage of the main semiconductor switch and the transfer function of the semiconductor switch. It should be noted that the transfer function used in the fourth step is the same transfer function used in the sixth step.

[0018] The subclaims show preferred developments of the invention.

[0019] Further preferably, the main semiconductor switch and the measuring semiconductor switch are each designed as an IGBT, as a MOSFET, or as a bipolar transistor, without thereby imposing a restriction to the semiconductor types mentioned.

[0020] The total ohmic voltage drop considered in the fifth method step preferably results from the voltage drop across the measuring resistor and particularly preferably additionally from a voltage drop across a wiring resistor and / or across a bond resistor. The wiring resistance results from the resistance of the lines used to connect the measuring resistor to the semiconductor switch. The wiring resistance can be determined, for example, by means of a separate, prior measurement of the lines and / or based on information about the dimensioning of the lines. The bond resistance results from the resistance of the bond wires via which the externally accessible terminals of the measuring semiconductor switch (via which the measurement is performed) are connected to internal terminals of the measuring semiconductor switch.By determining the corresponding voltage drops during the measurement based on the respective resistance values ​​of the wiring resistor and the bond resistor, and taking these into account when determining the total voltage drop, the collector current of the main semiconductor switch can be determined with particularly high accuracy. The ohmic .

[0021] Total voltage drop ΔU ge,R is preferably calculated as follows: ΔUge,R=Is×(Rs+Rw+Rb) where Is represents the measuring current, Rs the resistance of the measuring resistor, Rw the wiring resistance and Rb the bond resistance.

[0022] In a preferred embodiment of the present invention, in addition to measuring the voltage drop across the measuring resistor, a measurement of a common-mode interference is performed in order to compensate for the influence of the common-mode interference on the voltage drop. For this purpose, a first measuring line of the measuring arrangement is connected, for example, permanently to the emitter terminal of the main semiconductor switch, while a second measuring line of the measuring arrangement is connected, for example, alternately to the emitter terminal of the measuring semiconductor switch and to the emitter of the main semiconductor switch. If, in the case where both measuring lines are each connected to the emitter of the main semiconductor, a voltage drop deviating from zero is measured, this value can be used for compensation during the actual voltage measurement across the measuring resistor.This allows the accuracy of determining the collector current of the main semi-conductor switch to be further increased based on the method according to the invention. Particularly advantageously, the switching between the two measuring points to be measured by the second measuring line is carried out using a changeover switch, so that the arrangement of the two measuring lines remains unchanged between the two measurements, in order to avoid changing inductive coupling between the measuring lines and / or to implement particularly fast compensation of common-mode interference.

[0023] Preferably, the measurement of the voltage drop across the measuring resistor is carried out several times and the value of the voltage drop is preferably determined on the basis of the respective individual results of the multiple measurements and in particular on the basis of an average value over the respective individual results in order to filter out any interference that may be present.

[0024] In an advantageous embodiment of the present invention, the semiconductor switch, which comprises the main semiconductor switch and the measuring semiconductor switch, is embodied as a semiconductor chip and / or integrated into a semiconductor module, which in particular comprises at least one further main semiconductor switch. In the latter case in particular, a conventional individual measurement of the collector current of the main semiconductor switch is generally no longer possible, which is why the method according to the invention can be applied particularly advantageously in this case.

[0025] In a further advantageous embodiment of the present invention, the method further comprises a step for calibrating the measuring arrangement, on the basis of which the current and voltage values ​​for determining the collector current of the semiconductor switch are measured by measuring a collector current of the semiconductor switch to determine a deviation between the measured collector current and the collector current determined based on the measuring semiconductor switch. The determined deviation is then used to calibrate the measuring arrangement.

[0026] The calibration of the measuring arrangement is preferably carried out by adjusting the wiring resistance in order to substantially equalize the measured collector current and the determined collector current in a steady state of the semiconductor switch and / or by adjusting an inductance which causes the inductive voltage drop, so that respective times of a rising edge and / or a falling edge of the measured collector current (which is generated by a switch-on process and a subsequent switch-off process) and the determined collector current substantially coincide.

[0027] Preferably, the calibration is carried out on the basis of the same control of the semiconductor switch with which the collector current is determined, wherein in particular a sequence of the rising falling edge of the collector current is checked for plausibility by comparing an expected sequence of the edges with the measured sequence of the edges.

[0028] In a further advantageous embodiment of the present invention, in a case where a semiconductor module has a plurality of semiconductor switches, calibration is performed by switching on only the main semiconductor switch of the semiconductor module whose measuring semiconductor switch is used or accessible for determining the collector current of the semiconductor switch according to the invention. In a case where several measuring semiconductor switches are accessible from outside for a measurement according to the invention, the method according to the invention can be advantageously applied to further main semiconductor switches corresponding to the measuring semiconductor switches in order to be able to determine any deviations between the respective collector currents of the main semiconductor switches. This requires, in any case, that the respective semiconductor switches of the plurality of semiconductor switches in such a module can be controlled independently of one another. Short description of the drawings

[0029] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing: Fig. 1 a circuit diagram of an embodiment of a semiconductor according to the invention in conjunction with a measuring arrangement according to the invention; Fig. 2a shows an exemplary measuring arrangement for determining common-mode interference in a first measuring state; and Fig. 2b shows the exemplary measurement setup for determining common-mode interference in a second measurement state. Embodiments of the invention

[0030] Fig. Figure 1 shows a circuit diagram of an embodiment of a semiconductor according to the invention in conjunction with a measuring arrangement 10 according to the invention, on the basis of which a method according to the invention for measuring a collector current Ic of the semiconductor switch using a measuring resistor Rs can be carried out. The semiconductor according to the invention is embodied here as an IGBT.

[0031] The measuring arrangement 10 has an evaluation unit 20 designed as a microcontroller, a memory unit 30, a first measuring line 50 and a second measuring line 55, wherein the evaluation unit 20 is configured to carry out at least some of the steps of the method according to the invention.

[0032] For this purpose, a resistance value of the measuring resistor Rs is first measured with high accuracy using a four-wire measurement based on the measuring arrangement 10 and / or on a different arrangement. The measured value is advantageously stored in the memory unit 30 for subsequent use by the measuring arrangement 10.

[0033] The measuring arrangement 10 is connected to the measuring resistor Rs via the measuring lines 50, 55 and is thus configured to measure a voltage drop Us across the measuring resistor Rs in a state in which the measuring resistor Rs is connected between an emitter terminal E1 of a measuring semiconductor switch S1 of the semiconductor switch and an emitter terminal E2 of a main semiconductor switch S2 of the semiconductor switch.

[0034] In addition, respective collector terminals C1, C2 of the two semiconductor switches S1, S2 and respective gate terminals G1, G2 of the two semiconductor switches S1, S2 are electrically connected to each other, while a DC voltage UDC is applied between the collector terminals C1, C2 and the emitter terminals E1, E2.

[0035] The main semiconductor switch S1 has a first area which is here a factor of 1000 larger than a second area of ​​the measuring semiconductor switch S2.

[0036] The measuring arrangement 10 is designed to carry out the measurement of the voltage drop Us several times and to calculate a resulting voltage drop Us by averaging the respective measurement results.

[0037] The measuring arrangement 10 is further configured to calculate a measuring current Is from a quotient of the voltage drop Us across the measuring resistor Rs and the resistance value of the measuring resistor Rs.

[0038] In addition, the measuring arrangement 10 is configured to determine a gate-emitter voltage of the measuring semiconductor switch S1 on the basis of an area-adjusted current value, which results from a product of the measuring current Is and a quotient of the first area and the second area, and on the basis of a predefined transfer function of the semiconductor switch, which predefines a relationship between an internal gate-emitter voltage of the semiconductor switch and a collector current Ic of the semiconductor switch.

[0039] The transfer function is preferably a previously determined transfer function, which can be stored in the memory unit 30 in the form of data representing the transfer function.

[0040] The measuring arrangement 10 is further configured to determine a gate-emitter voltage of the main semiconductor switch S2 by adding to the gate-emitter voltage of the measuring semiconductor switch S2 an ohmic total voltage drop between the emitter E1 of the measuring semiconductor switch S1 and the emitter E2 of the main semiconductor switch S2 and an inductive voltage drop between the emitter E1 of the measuring semiconductor switch S1 and the emitter E2 of the main semiconductor switch S2.

[0041] Finally, the measuring arrangement 10 is configured to determine a collector current Ic of the main semiconductor switch based on the determined gate-emitter voltage of the main semiconductor switch S2 and the transfer function of the semiconductor switch.

[0042] Fig. 2a shows an exemplary measuring arrangement 10 for determining common-mode interference in a first measuring state.

[0043] In this first measuring state, a measuring resistor Rs, which is connected between an emitter terminal E1 of a measuring semiconductor switch S1 (see Fig. 1) and an emitter terminal of a measuring semiconductor switch S2 (see Fig. 1) is switched on, is measured via a first measuring line 50 and a second measuring line 55, since a changeover switch 40 has a first switching position.

[0044] Fig. 2b shows the exemplary measuring arrangement 10 from Fig. 2a for determining common-mode interference in a second measurement state.

[0045] In this second measuring state, the first measuring line 50 and a third measuring line 57 are used to measure on that side of the measuring resistor Rs which is connected to the emitter E2 of the main semiconductor switch S2, since the changeover switch 40 has a second switching position.

[0046] Information about a common mode interference measured in this measurement state can be advantageous for compensation of the measurement in Fig. 2a can be used to increase the accuracy of the measuring method according to the invention.

Claims

[1] Method for measuring a collector current (Ic) of a semiconductor switch by means of a measuring resistor (Rs) comprising: - a first step to determine a resistance value of the measuring resistor (Rs), - a second step for measuring a voltage drop (Us) across the measuring resistor (Rs) in a state in which the measuring resistor (Rs) is connected between an emitter terminal (E1) of a measuring semiconductor switch (S1) of the semiconductor switch and an emitter terminal (E2) of a main semiconductor switch (S2) of the semiconductor switch, wherein - respective collector terminals (C1, C2) of the two semiconductor switches (S1, S2) and respective gate terminals (G1, G2) of the two semiconductor switches (S1, S2) are electrically connected to each other, - a DC voltage (UDC) is applied between the collector terminals (C1, C2) and the emitter terminals (E1, E2), and - the main semiconductor switch (S1) has a first area which is larger than a second area of ​​the measuring semiconductor switch (S2), - a third step for determining a measuring current (Is) from a quotient of the voltage drop (Us) across the measuring resistor (Rs) and the resistance value of the measuring resistor (Rs), - a fourth step for determining a gate-emitter voltage of the measuring semiconductor switch (S1) based on - an area-adjusted current value, which results from a product of the measuring current (Is) and a quotient of the first area and the second area, and - a predefined transfer function of the semiconductor switch, which predefines a relationship between an internal gate-emitter voltage (Uge) of the semiconductor switch and a collector current (Ic) of the semiconductor switch, - a fifth step for determining a gate-emitter voltage of the main semiconductor switch (S2) by adding to the gate-emitter voltage of the measuring semiconductor switch (S2) an ohmic total voltage drop between the emitter (E1) of the measuring semiconductor switch (S1) and the emitter (E2) of the main semiconductor switch (S2) and, in particular, additionally an inductive voltage drop between the emitter (E1) of the measuring semiconductor switch (S1) and the emitter (E2) of the main semiconductor switch (S2), and - a sixth step for determining a collector current (Ic) of the main semiconductor switch based on the determined gate-emitter voltage of the main semiconductor switch (S2) and the transfer function of the semiconductor switch. [2] The method according to claim 1, wherein the main semiconductor switch and the measuring semiconductor switch are each formed as an IGBT, as a MOSFET, or as a bipolar transistor. [3] Method according to one of the preceding claims, wherein the total ohmic voltage drop results from the voltage drop (Us) across the measuring resistor (Rs) and in particular additionally from a voltage drop across a wiring resistor (Rw) and / or across a bond resistor (Rb). [4] Method according to one of the preceding claims, wherein in addition to measuring the voltage drop (Us) across the measuring resistor (Rs), a measurement of a common-mode interference is carried out in order to compensate for the influence of the common-mode interference on the voltage drop (Us). [5] Method according to one of the preceding claims, wherein the measurement of the voltage drop (Us) across the measuring resistor (Rs) is carried out several times and the value of the voltage drop (Us) is determined on the basis of respective individual results of the multiple measurements and in particular on the basis of an averaging of the respective individual results. [6] Method according to one of the preceding claims, wherein the semiconductor switch comprising the main semiconductor switch (S2) and the measuring semiconductor switch (S1), - is designed as a semiconductor chip, and / or - is integrated into a semiconductor module which in particular has at least one further main semiconductor switch. [7] Method according to one of the preceding claims, further comprising a step of calibrating a measuring arrangement on the basis of which the current and voltage values ​​for determining the collector current (Ic) of the semiconductor switch are measured by - a collector current of the semiconductor switch is measured in order to determine a deviation between the measured collector current and the collector current (Ic) determined on the basis of the measuring semiconductor switch (S1), and - a determined deviation is used to calibrate the measuring arrangement. [8] Method according to claim 7, wherein the measuring arrangement is calibrated by - the wiring resistance (Rw) is adjusted to substantially equalise the measured collector current and the determined collector current (Ic) in a steady state, and / or - an inductance (M) which causes the inductive voltage drop is adjusted so that respective times of a rising edge and / or a falling edge of the measured collector current and the determined collector current (Ic) substantially coincide. [9] Method according to claim 7 or 8, wherein the calibration is carried out on the basis of the same control of the semiconductor switch with which the collector current (Ic) is determined, wherein in particular a sequence of the rising falling edge of the collector current (Ic) is checked for plausibility. [10] Method according to one of claims 7 to 9, wherein in a case where a semiconductor module has a plurality of semiconductor switches, the calibration is carried out by switching on only that main semiconductor switch of the semiconductor module whose measuring semiconductor switch (S1) is used for determining the collector current (Ic) of the semiconductor switch according to the invention.

Images