Electric power converter and method for operating an electric power converter

Abstract

Electric power converter (1), comprising: • - a semiconductor switching element (10) having • (i) a first power terminal (13), • (ii) a second power terminal (14), • (iii) a control terminal (15), • (iv) a Kelvin terminal (19) and • (v) a switching path (20) formed between the first power terminal (13) and the Kelvin terminal (19) and switchable depending on a first voltage (21) across the control terminal (15) and the Kelvin terminal (19) so as to allow a current flow (22) from the first power terminal (13) to the second power terminal (14), when the switching path (20) is switched on; • - a driver (11) connected to the control terminal (15) and the Kelvin terminal (19) and configured to provide the first voltage (21) for switching on the switching path (20) upon receiving a control signal (17); and • - a detection circuit (12) configured to detect a second voltage (23) across the Kelvin terminal (19) and the second power terminal (14), to determine depending on the second voltage (23) a malfunction of the semiconductor switching element (10) and to control the driver (11) to switch off the switching path (20) upon determining the malfunction, the malfunction being an overcurrent and / or an operation in an active region.

Description

[0001] Electric power converter and method for operating an electric power converter

[0002] Field of the invention

[0003] The present invention relates to an electric power converter, comprising: a semiconductor switching element having a first power terminal, a second power terminal, a control terminal, a Kelvin terminal and a switching path formed between the first power terminal and the Kelvin terminal and switchable depending on a first voltage across the control terminal and the Kelvin terminal so as to allow a current flow from the first power terminal to the second power terminal, when the switching path is switched on; and a driver connected to the control terminal and the Kelvin terminal and configured to provide the first voltage for switching on the switching path upon receiving a control signal.

[0004] Aside, the invention relates to a method for operating an electric power converter.

[0005] Background of the invention

[0006] US 9 107318 B2 discloses a power converter comprising semiconductor modules with semiconductor devices. Each semiconductor device comprises a collector, an emitter, a gate and a Kelvin emitter. The Kelvin emitter provides a reference potential for the gate. A gate drive is provided to drive the semiconductor modules.

[0007] Semiconductor switching elements are a key component of electric power converters, such as inverters for converting the DC voltage into an AC voltage. In the case of a malfunction, high currents may flow through the path, which can damage or even destroy the semiconductor switching element. It is generally known to detect such a malfunction by detecting a voltage across the first power terminal and a second power terminal and to compare the detected voltage with a predetermined threshold value. Upon exceeding the threshold value, the semiconductor switching element is turned off.

[0008] Exemplarily, the datasheet “ISO5451 High-CMTI 2.5-A and 5-A Isolated IGBT, MOSFET Gate Driver With Active Protection Features” by Texas instruments (SLLSEO1 D - June 2015 - revised May 2023) discloses a gate driver with a desaturation (DESAT) pin to be connected via one or multiple desaturation diodes with the collector. A blanking capacitor between the pin and the emitter disables DESAT detection during the off-to-on transition. Therein, an internal current source charges the blanking capacitance slowly. If the voltage across the capacitance reaches a value causing the desaturation diode to be conducting, the voltage across the collector and emitter terminal can be detected. The threshold value is determined by an internal reference voltage and the number of desaturation diodes in series. Therein, by choosing the number of desaturation diodes the threshold value can be decreased.

[0009] Such a desaturation detection circuit has several drawbacks: It is not possible to choose a threshold voltage that is above the internal reference voltage of the driver. Further, for a threshold voltage highly below the reference voltage, a large number of desaturation diodes is necessary. Also, the voltage across the first and the second power terminal is temperature dependent so that the actual current, at which a desaturation is detected, is highly varying. Further, charging the external capacitance takes time, before the malfunction can be detected. In particular with regard to fast switching SiC-MOSFETs as semiconductor switching elements, this time may be too long for safely turning off the semiconductor switching element.

[0010] Summary of the invention

[0011] It is an object of the invention to provide an improved possibility for detecting a malfunction of a semiconductor switching element in an electric power converter. According to the invention, this object is solved by an electric power converter as initially described, further comprising a detection circuit configured to detect a second voltage across the Kelvin terminal and the second power terminal, to determine depending on the second voltage a malfunction of the semiconductor switching element and to control the driver to switch off the switching path upon determining the malfunction, the malfunction being an overcurrent and / or an operation in an active region.

[0012] The electric power converter according to the invention comprises a semiconductor switching element. The semiconductor switching element has a first power terminal, a second power terminal, a control terminal, a Kelvin terminal and a switching path. The switching path is formed between the first power terminal and the Kelvin terminal. The switching path is switchable depending on a first voltage so as to allow a current flow from the first power terminal to the second power terminal, when the switching path is switched on. The first voltage is across the control terminal and the Kelvin terminal. The electric power converter further comprises a driver. The driver is connected to the control terminal and the Kelvin terminal. The driver is configured to provide the first voltage for switching on the switching path upon receiving a control signal. The electric power converter further comprises a detection circuit. The detection circuit is configured to detect a second voltage. The second voltage is across the Kelvin terminal and the second power terminal. The detection circuit is further configured to determine depending on the second voltage a malfunction of the semiconductor switching element. The detection circuit is further configured to control the driver to switch off the switching path upon determining the malfunction. The malfunction is an overcurrent / or an operation in the active region.

[0013] The present invention is based upon the consideration that there are parasitic components of the semiconductor switching element between the Kelvin terminal and the second power terminal. A voltage drop across these parasitic components depends on the current flow from the first power terminal to the second power. Therefore, by detecting the second voltage, it can be determined, whether the overcurrent and / or the operation in the active region occurs. Advantageously, conventional desaturation pins with additional external capacitance can be avoided, so as to allow a fast detection of the malfunction.

[0014] The electric power converter may be designed as an inverter, as a DC / DC converter or as an active rectifier.

[0015] The semiconductor switching element may be an insulated gate bipolar transistor (IGBT). In this case the first power terminal may be the source terminal, the second power terminal may be a emitter terminal and the control terminal may be a gate terminal. Further with regard to an IGBT, the active region may be the desaturation region of the IGBT. Alternatively, the semiconductor switching element may be a power MOSFET, preferably a SiC-MOSFET. In this case, the first power terminal may be a drain terminal, the second power terminal may be a source terminal and the control terminal may be a gate terminal. The active region may be at a saturated operation region of the power MOSFET. Obviously, the semiconductor switching element may also alternatively be a Gallium Nitride Field Effect Transistor.

[0016] Between the Kelvin terminal and the second power terminal, the semiconductor switching element may comprise a metal conductor causing a resistance of 1 pQ to 1 mQ, preferably 10 pQ to 100 pQ and / or an inductance between 100 pH and 100 nH, preferably 1 nH to 10 nH.

[0017] Preferably, the detection circuit is configured to determine the malfunction depending on that the second voltage reaches or crosses a predetermined threshold level. The threshold value may be chosen between 1 and 20 V.

[0018] Preferably, the driver comprises a first supply terminal for obtaining a positive supply voltage between the first supply terminal and the Kelvin terminal and a second supply terminal for obtaining a negative supply voltage between the second supply terminal and the Kelvin terminal. The driver may be further configured to connect the first supply terminal to the control terminal, when the control signal indicates to switch on the switching path, and to connect the second supply terminal to the control terminal, when the control signal indicates to switch of the switching path. Typically, connecting the first supply terminal to the control terminal causes a positive voltage, in particular between 10 and 20 V, between the control terminal and the Kelvin terminal. Connecting the second supply terminal to the control terminal may cause a negative voltage, preferably between -10 and -1 V, between the control terminal and the Kelvin terminal.

[0019] The detection circuit may comprise a comparator having a first comparator input terminal, a second comparator input terminal and a comparator output terminal. The detection circuit may be configured to provide an input signal depending on the second voltage to the first comparator input terminal, to provide a reference signal depending on the threshold level to the second comparator input terminal and to control the driver to switch of the switching path depending on an output signal at the comparator output terminal. Preferably, the comparator is supplied by the first supply terminal and the second supply terminal.

[0020] Further, the detection circuit may comprise an input circuit with a first input terminal connected to the first supply terminal, a second input terminal connected to the second power terminal and an output terminal. The input circuit may be configured to provide a third voltage at the output terminal as the input signal. The third voltage may refer to a potential at the second power terminal.

[0021] Preferably, the input circuit is a voltage divider with a first resistor connected to the first input terminal, a second resistor connected to the second input terminal and a tap between the resistors connected to the output terminal. Advantageously, the threshold value can be adapted by choosing the values of the first and second resistor.

[0022] Further, the detection circuit may comprise a reference voltage source connected between the second comparator input terminal and the Kelvin terminal and configured to provide a reference voltage as the reference signal. Also, by choosing the reference voltage, the threshold value can be adapted.

[0023] In detail, it is preferred that the detection circuit is configured to provide the output signal when the second voltage becomes greater than a difference of the ratio of the resistance of the second resistor to the resistance of the first resistor multiplied by the positive supply voltage and the reference voltage. I.e., the output signal may be provided, when wherein U2 denotes the second voltage, R1 denotes the resistance of the first resistor, R2 denotes the resistance of the second resistor, UDD denotes the positive supply voltage and Uref denotes the reference voltage.

[0024] Advantageously, the detection circuit comprises a clamping circuit comprising a first diode connected in forward direction from the first comparator input terminal to the first supply terminal and the second diode connected in forward direction from the Kelvin terminal to the second comparator input terminal. The clamping circuit protects the input of the comparator, e.g., in cases when a high and fast rising current is detected.

[0025] With regard to the electric power converter according to the invention, it is preferred that the determining the malfunction by the detection circuit is inactive, when the switching path is switched off and / or during a predetermined delay time starting, when the switching path is switched on. When switching on the switching path without malfunction the current commutates with several kA / ps causing an increase of the voltage over the parasitic components. This voltage may be above the threshold value. After the commutation, the second voltage decrease to a value below the threshold. Thus, it is preferred not to detect a malfunction if the second voltage is above the threshold shortly after switching on the switching path. Rather, in the case of the malfunction the second voltage, continues to increase until the delay time has expired or rises after the delay time has expired. The delay time may amount at least 50 ns, preferably at least 75 ns, more preferably at least 100 ns, and / or at most 500 ns, preferably at most 300 ns, more preferably at most 200 ns.

[0026] The detection circuit may further comprise a delay element connected between the comparator output terminal and the driver and configured to block the output signal during the delay time. The delay element may comprise a timer configured to be triggered to start the delay time when the control signal is indicative of switching on the switching path.

[0027] Preferably, the semiconductor switching element, the driver and the detection circuit form a first commutation arrangement. The electric power converter may further comprise a ground plane and a second commutation arrangement corresponding to the first one. Particularly, the second power terminal of the second commutation arrangement is connected to the first power terminal of the first commutation arrangement and the second power terminal of the first commutation arrangement is connected to the ground plane. Alternatively, the second power terminal of the first commutation arrangement may be connected to the first power terminal of the second commutation arrangement and the second power terminal of the second commutation arrangement may be connected to the ground plane.

[0028] Further, the above object is solved by a method for operating an electric power converter, the electric power converter comprising: a semiconductor switching element having a first power terminal, a second power terminal, a control terminal, a Kelvin terminal and a switching path formed between the first power terminal and the Kelvin terminal and switchable depending on a first voltage across the control terminal and the Kelvin terminal so as to allow a current flow from the first power terminal to the second power terminal, when the switching path is switched on; a driver connected to the control terminal and the Kelvin terminal; and a detection circuit; the method comprising steps of providing, by the driver, the first voltage for switching on the switching path upon receiving a control signal; detecting, by the detection circuit, a second voltage across the Kelvin terminal and the second power terminal; determining, by the detection circuit, depending on the second voltage a malfunction of the semiconductor switching element, the malfunction being an overcurrent and / or an operation in an active region; and controlling, by the detection circuit, the driver to switch off the switching path upon determining the malfunction.

[0029] Preferably, determining the malfunction by the detection circuit is inactive, when the switching path is switched off and / or during a predetermined delay time starting, when the switching path is switched on, and the malfunction is detected depending on that the second voltage reaches or crosses a predetermined threshold level.

[0030] Preferably, when no malfunction is determined, the second voltage increases upon switching on the switching path and decreases before the delay time has expired.

[0031] Preferably, when the malfunction causes a short-circuit or an overcurrent in the switching path at the time of switching on the switching path and the second voltage increases upon switching on the switching path, wherein the malfunction is determined when the second voltage is above the threshold level at the time of expiry of the delay time.

[0032] Preferably, the switching path is switched on without the malfunction and the malfunction occurs after expiry of the delay time and causes a short-circuit or an overcurrent in the switching path at the time of switching on the switching path, the second voltage increases upon switching on the switching path, decreases and remains below the threshold level before and after expiry of the delay time and increases due to the malfunction, wherein the malfunction is determined when the second voltage is above the threshold level after expiry of the delay time. All statements concerning the electric power converter according to the invention apply analogously to the method according to the invention so that the above advantages can be achieved with the method as well.

[0033] Brief description of the drawings

[0034] Further details and advantages of the invention are disclosed in the following, wherein reference is made to the drawings, which show schematically:

[0035] Fig. 1 a block diagram of an embodiment of an electric power converter according to the invention;

[0036] Fig. 2 a circuit diagram of the detection circuit and the driver according to the embodiment;

[0037] Fig. 3 diagrams of voltages, a current and an operating state of the electric power converter without malfunction;

[0038] Fig. 4 diagrams of the voltages, the current and the operating state, when a short- circuit of the switching path is present on switching on the switching path; and

[0039] Fig. 5 diagrams of the voltages, the current and the operating state, when a short- circuit occurs and the switching path is switched on.

[0040] Fig. 1 is a block diagram of an embodiment of an electric power converter 1 .

[0041] In the present embodiment, the electric power converter 1 is exemplarily designed as inverter configured to convert DC voltage provided by an external DC voltage source 2 into a three-phase AC voltage for an electric motor 3. Therein, the electric power converter 1 comprises a positive DC supply line 4 and a negative DC supply line 5 forming a ground plane 6 of the electric power converter 1 . For each phase of the AC voltage, the electric power converter 1 comprises a half bridge 7 connected between the positive and negative DC supply lines 4, 5. Each half bridge 7 comprises a first commutation arrangement 8 and the second commutation arrangement 9.

[0042] Each commutation arrangement 8, 9 comprises a semiconductor switching element 10, a driver 11 and the detection circuit 12. The semiconductor switching element comprises a first power terminal 13, a second power terminal 14 and a control terminal 15. In the present embodiment, the second power terminal 14 of the second commutation arrangement 9 is connected to the first power terminal 13 of the first commutation arrangement 8 and the second power terminal 14 of the first commutation arrangement 8 is connected to the ground plane 6. The first power terminal of the second commutation arrangement 9 is connected to the positive DC supply line 4.

[0043] Further, the electric power converter 1 comprises a controller 16 configured to provide a control signal 17 to the driver 11 of respective one of the semiconductor switching elements 10.

[0044] Fig. 2 is a circuit diagram of one of the commutation arrangements 8, 9 according to the embodiment.

[0045] The semiconductor switching element 10 further comprises a Kelvin terminal 19 and a switching path 20 formed between the first power terminal 13 and the Kelvin terminal 19. The switching path 20 is switchable depending on a first voltage 21 across the control terminal 15 and the Kelvin terminal 19 so as to allow a current flow 22 from the first power terminal 13 to the second power terminal 14, when the switching path is switched on. The driver circuit 11 is connected to the control terminal 15 and the Kelvin terminal 19 and configured to provide the first voltage 21 for switching on the switching path 20 upon receiving the control signal. The detection circuit 12 is configured to detect a second voltage 23 across the Kelvin terminal 19 and the second power terminal 14 and to determine depending on the second voltage 23 a malfunction of the semiconductor switching element 10. The malfunction is an overcurrent and an operation of the semiconductor switching element 10 in an active region. Upon detecting the malfunction, the detection circuit 12 controls the driver 11 to switch off the switching path 20.

[0046] As can be seen in Fig. 2, the semiconductor switching element 10 is a power MOSFET, e.g., a SiC-MOSFET. Therefore, the first power terminal 13 is a drain terminal, the second power terminal 14 is a source terminal and the control terminal 15 is a gate terminal. In this case, the active region is a saturated region in the operational characteristics of the power MOSFET. Accordingly, the malfunction refers to an operation of the MOSFET in the saturated region and to an overcurrent through the switching path 20 in a linear region of the MOSFETs operation characteristics.

[0047] Between the Kelvin terminal 19 and the second power terminal 14, there is a metal conductor, which is modeled by parasitic components, i.e., a series connection of an inductance Lpand a resistance RP. Thus, the second voltage 23 corresponds to the voltage dropping across these parasitic components. Consequently, the second voltage 23 is a function of the current 22 so that the malfunction can be detected based on the second voltage 23.

[0048] In detail, the detection circuit 12 is configured to determine the malfunction depending on that the second voltage 23 reaches or crosses a predetermined threshold level. Thereto, the driver comprises a first supply terminal 24 for obtaining a positive supply voltage 25 between the first supply terminal 24 and the Kelvin terminal 19 and a second supply terminal 26 for obtaining a negative supply voltage 27 between the second supply terminal 26 and the Kelvin terminal 19. A voltage source 25a for the positive supply voltage 25 and a voltage source 27a for the negative supply voltage 27 may be part of the electric power converter 1 or the commutation arrangement 8, 9, respectively, as well. The driver 11 is configured to connect the first supply terminal 24 to the control terminal 15, when the control signal 17 indicates to switch on the switching path 20, and to connect the second supply terminal 26 to the control terminal 15, when the control signal 17 indicates to switch off the switching path 20. In the present embodiment, connecting the respective supply terminals 24, 26 to the control 15 is realized by a push pull stage 28. An optional gate resistor 29 is located between the push pull stage 28 and the control 15 and is part of the driver 11 as well. As an alternative, the optional gate resistor 29 is not part of the driver 11 .

[0049] The detection circuit 12 comprises a comparator 30 having a first comparator input terminal 31 , a second comparator input terminal 32 and a comparator output terminal 33. The detection circuit 12 is configured to provide an input signal 34 depending on the second voltage 23 to the first comparator input terminal 31 . A positive supply terminal 35 of the comparator 30 is connected to the first supply terminal 24 and a negative supply terminal 36 of the comparator 30 is connected to the second supply terminal 26.

[0050] Further, the detection circuit 12 comprises a reference voltage source 37 for providing a reference signal 38 depending on the threshold level to the second comparator input terminal 32. The reference voltage source 37 is connected between second comparator input 32 terminal and the Kelvin terminal 19 and configured to provide a reference voltage as the reference signal 38. Depending on an output signal 39 at the comparator output 33, the detection circuit 12 controls the driver 11 to switch off the switching path 20. E.g., the driver 11 is configured to overrule the control signals 17 upon being controlled to switch off the switching path 20 depending on the output signal 39.

[0051] In further detail, the detection circuit comprises an input circuit 40 with a first input terminal 41 connected to the first supply terminal 24, a second input terminal 42 connected to the second power terminal 14 and an output terminal 43. The input circuit 40 is configured to provide a third voltage 44 at the output terminal 43 as the input signal 34. Therein, the third voltage 44 is referred to a potential at the second power terminal 14. The input circuit 40 is realized by a voltage divider 45 with a first resistor 46 connected to the first input terminal 41 , a second resistor 47 connected to the second input terminal 42 and a tap 48 between the resistors 46, 47. The tap 48 is connected to the output terminal 43.

[0052] Accordingly, the output signal is to be provided, when wherein U2 denotes the second voltage 23, R1 denotes the resistance of the first resistor 46, R2 denotes the resistance of the second resistor 47, UDD denotes the positive supply voltage 25 and Uref denotes the reference voltage provided by the reference voltage source 37.

[0053] In order to protect the comparator 30 from fast rising and high voltages at the output terminal 43, the detection circuit 12 is provided with a clamping circuit 49. The clamping circuit 49 comprises a first diode 50 connected in forward direction from the first comparator input terminal 31 to the first supply terminal 24 and a second diode 51 connected in forward direction from the Kelvin terminal 19 to the second comparator input terminal 32.

[0054] In the present embodiment, the determining of the malfunction is inactive, when the switching path 20 is switched off and during a predetermined delay time starting, when the control signal becomes indicative of switching on the switching path 20. Further, the detection circuit 12 comprises a delay element 52 determining the malfunction by the detection circuit is inactive, when the switching path is switched off and during a predetermined delay time starting, when the switching path 20 is switched on. I.e., The output signal 39 is provided to the driver 11 only if, cumulatively, the switching path 20 is controlled to be switched on and the delay time has expired. Thereto, the delay element 52 blocks transmission of the output signal 39 to the driver 11 during the delay time. Exemplarily, the delay element 52 may comprise a timer being triggered by the control signal 17 changing its signal state to switching on the switching path 20. Regarding the implementation of the driver 11 and the detection circuit, at least the driver 11 , the comparator 30, the delay element 52 and the reference voltage source 37 may be implemented by an integrated circuit, whereas the input circuit 40 is realized by external elements connected to the integrated circuit. This allows to widely vary the threshold level by choosing the values of the resistors 46, 47.

[0055] In the following, the function of the electric power converter 1 is explained in further detail with regard to Fig. 3 to Fig. 5, each showing diagrams of voltages, currents and an operating state 53 of the electric power converter 1 over time t. Therein, the upper diagram shows a gate-source voltage Ugs corresponding to the first voltage 21 , the second diagram shows a drain current Id corresponding to current flow 22, the third diagram shows a voltage Up over the parasitic components corresponding to the second voltage 23 and the lower diagram illustrates the operating state 53. Therein, the progress of the voltages and currents Ugs, Id, Up is illustrated qualitatively.

[0056] Fig. 3 refers to a case without malfunction.

[0057] At a time to the control signal 17 is indicative for switching on the switching path 20 causing the driver 11 to provide the positive supply voltage 25 to the gate or control terminal 15, respectively. Consequently, the gate-source voltage Ugs rises. Starting from to the drain current Id rises with approximately several kiloamperes per microsecond and the voltage Up steps up to several volts. At a time ti, which is approximately 100 to 200 ns later than to, the voltage Up steps back to several hundreds of millivolts (because of the resistance Rp , since the drain current Id remains substantially constant or increases very slowly or decreases very slowly.

[0058] As depicted in the lower diagram, the operating state 52 is inactive (level 54) before to as the switching path 20 is switched off. At time to the timer in the delay element 52 is triggered as indicated by level 55. At time t2 the delay time has expired. As the voltage Up is below the threshold level indicated by level 57, the output signal 39 is not indicative of switching off the switching path 20 due to a malfunction.

[0059] Fig. 4 refers to a case, when a short-circuit of the switching path 20 is present on switching on the switching path.

[0060] Until the ti the case of a short-circuit causing the malfunction and being already present, when switching on the switching path 20, cannot be distinguished from the case without malfunction in Fig. 3. However, after time ti the current Id and the voltage Up continue increasing. At time ts>, the detection circuit 12 detects that the voltage Up is above the threshold level and provides the output signal 39 so as to switch off the switching path 20 by providing the negative supply voltage 27 to the control terminal 15.

[0061] Fig. 5 refers to, when a short-circuit occurs and the switching path 20 is already switched on.

[0062] Here, the malfunction occurs at time t3 so that the diagram in Fig. 5 correspond to those in Fig. 3 before to and between to and t3. At time ta, voltage Up and current Id step up and start increasing, whereby voltage Up crosses the threshold level. After a short reaction time, the detection circuit 12 detects that the voltage Up respectively, is above the threshold level and provides the output signal 39 so as to switch off the switching path 20 by providing the negative supply voltage 27 to the control terminal 15.

[0063] According to another embodiment, the semiconductor switching element 10 is an IGBT. Then, the first power terminal 13 is a collector terminal, the second power terminal 14 is an emitter terminal and the control terminal 15 is a gate terminal. In this case, the active region is a desaturated region in the operational characteristics of the IGBT. Accordingly, the malfunction refers to an operation of the IGBT in the desaturated region and an overcurrent through the switching path 20 in the saturated region of the IGBTs operation characteristics. According to further embodiments, corresponding to the afore-mentioned ones, the second power terminal of the first commutation arrangement is connected to the first power terminal of the second commutation arrangement and the second power terminal of the second commutation arrangement is connected to the ground plane.

[0064] Although the electric power converter 1 has been explained by an implementation of an inverter, the electric power converter 1 may be a DC / DC converter or an active rectifier according to further embodiments.

Claims

Claims1 . Electric power converter (1 ), comprising:- a semiconductor switching element (10) having(!) a first power terminal (13),(ii) a second power terminal (14),(iii) a control terminal (15),(iv) a Kelvin terminal (19) and(v) a switching path (20) formed between the first power terminal (13) and the Kelvin terminal (19) and switchable depending on a first voltage (21) across the control terminal (15) and the Kelvin terminal (19) so as to allow a current flow (22) from the first power terminal (13) to the second power terminal (14), when the switching path (20) is switched on; and- a driver (11) connected to the control terminal (15) and the Kelvin terminal (19) and configured to provide the first voltage (21) for switching on the switching path (20) upon receiving a control signal (17); characterized by- a detection circuit (12) configured to detect a second voltage (23) across the Kelvin terminal (19) and the second power terminal (14), to determine depending on the second voltage (23) a malfunction of the semiconductor switching element (10) and to control the driver (11) to switch off the switching path (20) upon determining the malfunction, the malfunction being an overcurrent and / or an operation in an active region.

2. Electric power converter according to claim 1 , wherein the detection circuit (12) is configured to determine the malfunction depending on that the second voltage (23) reaches or crosses a predetermined threshold level.

3. Electric power converter according to claim 2, wherein the driver (11) comprises a first supply terminal (24) for obtaining a positive supply voltage (25) between the first supply terminal (24) and the Kelvin terminal (19) anda second supply terminal (26) for obtaining a negative supply voltage (27) between the second supply terminal (26) and the Kelvin terminal (19) and is configured to connect the first supply terminal (24) to the control terminal (15), when the control signal (17) indicates to switch on the switching path (20), and to connect the second supply terminal (26) to the control terminal (15), when the control signal (17) indicates to switch off the switching path (20).

4. Electric power converter according to claim 2 or 3, wherein the detection circuit (12) comprises a comparator (30) having a first comparator input terminal (31), a second comparator input terminal (32) and a comparator output terminal (33), the detection circuit (12) being configured to provide an input signal (34) depending on the second voltage (23) to the first comparator input terminal (31), to provide a reference signal (38) depending on the threshold level to the second comparator input terminal (32) and to control the driver (11) to switch off the switching path (20) depending on an output signal (39) at the comparator output terminal (33).

5. Electric power converter according to claim 4, wherein the detection circuit (12) comprises an input circuit (40) with a first input terminal(41) connected to the first supply terminal (24), a second input terminal (42) connected to the second power terminal (14) and an output terminal (43), the input circuit (40) being configured to provide a third voltage (44) at the output terminal (43) as the input signal (34), the third voltage (44) referring to a potential at the second power terminal (14).

6. Electric power converter according to claim 5, wherein the input circuit (40) is a voltage divider (45) with a first resistor (46) connected to the first input terminal (41), a second resistor (47) connected to the second input(42) terminal and a tap (48) between the resistors (46, 47) connected to the output terminal (43).

7. Electric power converter according to any of claims 4 to 6, whereinthe detection circuit (12) comprises a reference voltage source (37) connected between second comparator input terminal (32) and the Kelvin terminal (19) and configured to provide a reference voltage as the reference signal (38).

8. Electric power converter according to claims 6 and 7, wherein the detection circuit (12) is configured to provide the output signal (39), when the second voltage (23) becomes greater than a difference of the ratio of the resistance of the second resistor (47) to the resistance of the first resistor (46) multiplied by the positive supply voltage (25) and the reference voltage.

9. Electric power converter according to any of claims 4 to 8, wherein the detection circuit (12) comprises a clamping circuit (49) comprising a first diode (50) connected in forward direction from the first comparator input terminal (31) to the first supply terminal (24) and a second diode (51) connected in forward direction from the Kelvin terminal (19) to the second comparator input terminal (32).

10. Electric power converter according to any of the preceding claims, wherein determining the malfunction by the detection circuit (12) is inactive, when the switching path (20) is switched off and / or during a predetermined delay time starting, when the switching path (20) is switched on.11 . Electric power converter according to any of the preceding claims, wherein the semiconductor switching element (10), the driver (11) and the detection circuit (12) form a first commutation arrangement (8), wherein the electric power converter (1) further comprises- a ground plane (6); and- a second commutation arrangement (9) corresponding to the first one; wherein the second power terminal (14) of the second commutation (9) arrangement is connected to the first power terminal (13) of the first commutation arrangement (8) and the second power terminal (14) of the first commutation arrangement (8) is connected to the ground plane (6) orwherein the second power terminal (14) of the first commutation arrangement (8) is connected to the first power terminal (13) of the second commutation arrangement (9) and the second power terminal (14) of the second commutation (9) arrangement is connected to the ground plane (6).

12. Method for operating an electric power converter (1 ), the electric power converter comprising:- a semiconductor switching element (10) having a first power terminal (13), a second power terminal (14), a control terminal (15), a Kelvin terminal (19) and a switching path (20) formed between the first power terminal (13) and the Kelvin terminal (19) and switchable depending on a first voltage (21) across the control terminal (15) and the Kelvin terminal (19) so as to allow a current flow (22) from the first power terminal (13) to the second power terminal (14), when the switching path (20) is switched on;- a driver (11) connected to the control terminal (15) and the Kelvin terminal (19); and- a detection circuit (12); the method comprising steps of- providing, by the driver (11 ), the first voltage (21 ) for switching on the switching path (20) upon receiving a control signal (17);- detecting, by the detection circuit (12), a second voltage (23) across the Kelvin terminal (19) and the second power terminal (14);- determining, by the detection circuit (12), depending on the second voltage (23) a malfunction of the semiconductor switching element (10), the malfunction being an overcurrent and / or an operation in an active region; and- controlling, by the detection circuit (12), the driver (11 ) to switch off the switching path (20) upon determining the malfunction.

13. Method according to claim 12, wherein determining the malfunction by the detection circuit (12) is inactive, when the switching path (20) is switched off and / or during a predetermined delay timestarting, when the switching path (20) is switched on, and the malfunction is detected depending on that the second voltage (23) reaches or crosses a predetermined threshold level.

14. Method according to claim 13, wherein when the malfunction causes a short-circuit or an overcurrent in the switching path (20) at the time of switching on the switching path (20) and the second voltage (23) increases upon switching on the switching path (20), wherein the malfunction is determined when the second voltage (23) is above the threshold level at the time of expiry of the delay time.

15. Method according to claim 13 or 14, wherein when the switching path (20) is switched on without the malfunction and the malfunction occurs after expiry of the delay time and causes a short-circuit or an overcurrent in the switching path (20) at the time of switching on the switching path (20), the second voltage (23) increases upon switching on the switching path (20), decreases and remains below the threshold level before and after expiry of the delay time and increases due to the malfunction, wherein the malfunction is determined when the second voltage (23) is above the threshold level after expiry of the delay time.

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