CONTROLLING A METAL OXIDE SEMICONDUCTOR FIELD EFFECTIVE TRANSISTOR

Description

[0001] The invention relates to a method and a control arrangement for controlling a metal-oxide-semiconductor field-effect transistor (MOSFET), in particular a MOSFET based on a wide-bandgap semiconductor.

[0002] A MOSFET is reverse-conducting and has a pn junction between bulk and drain, which, when the bulk and source are electrically connected, acts as an intrinsic diode, known as the inverse diode or the body diode of the MOSFET. Reverse currents flow through the body diode when the MOSFET is off. Because the body diode has a high resistance, this results in high losses. Significant losses of this type can occur, particularly in a power converter implemented using MOSFET technology if, in the event of a fault, all of the converter's MOSFETs are turned off and reverse currents from a supply network connected to the converter or a load connected to the converter flow through the body diodes of the converter's MOSFETs.Currently, certain power converters, such as traction converters, are increasingly using MOSFETs based on wide-bandgap semiconductors, such as silicon carbide or gallium nitride, which are subject to high current loads. This poses a particular problem in these power converters: reverse currents through the MOSFETs can lead to high losses in the event of a fault-related shutdown of all MOSFETs.

[0003] The document Texas Instruments: "UCD7138 4-A and 6-A Single-Channel Synchronous-Rectifier Driver With Body-Diode Conduction Sensing and Reporting", May 31, 2015 (2015-05-31), URL: http: / / www.ti.com / lit / ds / symlink / ucd7138.pdf discloses a MOSFET driver with a gate driver, a circuit for sensing a body-diode conduction state, and a circuit for optimizing a turn-on delay.

[0004] DE 11 2016 002 958 T2 discloses a method for controlling an electric power steering device comprising a plurality of inverter bridges, each connected to a multiphase motor configured to provide power assistance for steering a vehicle. The method comprises, upon detection of a failure within one of the inverter bridges, controlling the current flow within the faulty inverter bridge and using one or more of the other inverter bridges to provide power assistance.

[0005] Helen Ding: "IR11688 Smart Rectifier(TM) Control 1C Design Notes", July 31, 2015 (2015-07-31), pages 1-35, XP055715572, found on the Internet: URL:https: / / www.infineon.com / dgdl / lnfineon-ApplicationNote-1R11688-SmartRectifier-Control-1C-DesignNotes-AN-v01_00-EN.pdf fileld=5546d46253f65057015418afca1 d4d20 [found on 2020-07-16] discloses a method for controlling a MOSFET.

[0006] The invention is based on the object of specifying a method and a control arrangement for controlling a MOSFET which are improved with regard to the reduction of losses caused by reverse currents.

[0007] The object is achieved according to the invention by a method having the features of claim 1 and a control arrangement having the features of claim 5.

[0008] Advantageous embodiments of the invention are the subject of the subclaims.

[0009] The method according to the invention relates to the control of a MOSFET, in particular a MOSFET based on a wide-bandgap semiconductor, having a drain terminal, a source terminal, a gate terminal, and a body diode, wherein the MOSFET is arranged in a power converter comprising multiple MOSFETs. After a fault occurs that has led to the shutdown of all MOSFETs in the power converter, it is monitored whether the body diode of the MOSFET is electrically conductive. The MOSFET is switched on when the body diode is electrically conductive, and the MOSFET is controlled depending on a control signal when the body diode is electrically blocking.

[0010] The invention therefore provides for switching on a MOSFET if its body diode is conductive and thus conducting current after a fault has occurred that has led to the shutdown of all MOSFETs in the power converter. By switching on the MOSFET, reverse currents that would flow solely through the body diode when the MOSFET is off are at least partially conducted through the MOSFET channel between the source terminal and the drain terminal, so that reverse currents flowing through the body diode and the losses caused by them are greatly reduced. If the body diode is electrically blocking, the MOSFET is controlled as usual depending on a control signal, so that the control of the MOSFET is not changed in this case.

[0011] The invention further provides that a first voltage threshold is specified for a drain-source voltage between the drain terminal and the source terminal of the MOSFET, the drain-source voltage is detected, and it is concluded that the body diode is electrically conductive when the drain-source voltage falls below the first voltage threshold. Furthermore, a second voltage threshold is specified for the drain-source voltage, and it is concluded that the body diode is electrically blocking when the drain-source voltage exceeds the second voltage threshold. For example, both voltage thresholds are negative and the second voltage threshold is greater than the first voltage threshold.

[0012] The aforementioned aspects of the invention utilize the drain-source voltage to detect whether the MOSFET's body diode is electrically conductive or blocking. Voltage thresholds are used for this purpose; exceeding or falling below these thresholds signals that the body diode is electrically conductive or blocking, respectively.

[0013] One embodiment of the invention provides that a first current threshold value is specified for a drain-source current of a drain-source current flowing in a forward direction of the body diode between the drain terminal and the source terminal of the MOSFET, the drain-source current is detected, and it is concluded that the body diode is electrically conductive when the drain-source current exceeds the first current threshold value. Furthermore, a second current threshold value for the drain-source current, which is smaller than the first current threshold value, can be specified, and it is concluded that the body diode is electrically blocking when the drain-source current falls below the second current threshold value.

[0014] The invention provides that the direction of a drain-source current flowing between the drain terminal and the source terminal of the MOSFET is detected, and it is concluded that the body diode is electrically conductive when the drain-source current flows in a forward direction of the body diode. Furthermore, it can be concluded that the body diode is electrically blocking when the drain-source current flows opposite to the forward direction of the body diode.

[0015] The invention uses the drain-source current to detect whether the body diode is electrically conductive or blocking. For this purpose, current threshold values ​​are used for the current intensity of the drain-source current in the forward direction of the body diode; if these values ​​are exceeded or not, this signals that the body diode is electrically conductive or blocking, respectively. The drain-source current intensity is measured, for example, using a shunt resistor arranged in the current path of the drain-source current. Alternatively or additionally, the direction of the drain-source current is detected to detect whether the body diode is electrically conductive or blocking. The direction of the drain-source current is determined, for example, by counting the triggered voltage pulses or by a flip-flop that changes its state with each triggered voltage pulse.

[0016] A control arrangement according to the invention for carrying out the method according to the invention comprises a monitoring unit which is designed to determine whether the body diode is electrically conductive or blocking, and a control unit which is designed to switch on the MOSFET after the occurrence of a fault which has led to all MOSFETs of the power converter being switched off, if the monitoring unit determines that the body diode is electrically conductive, and to control the MOSFET in dependence on the control signal if the body diode is electrically blocking.

[0017] The monitoring unit is designed to detect the drain-source voltage and, based on the drain-source voltage, to determine whether the body diode is electrically conductive or blocking. Embodiments of the control arrangement according to the invention provide that the monitoring unit is designed to detect the drain-source current and, based on the drain-source current, to determine whether the body diode is electrically conductive or blocking, and / or that the monitoring unit is designed to detect the direction of the drain-source current and, based on the direction of the drain-source current, to determine whether the body diode is electrically conductive or blocking.

[0018] A further embodiment of the control arrangement according to the invention provides that the monitoring unit is designed to inform the control unit via an additional control signal whether the body diode is electrically conductive or blocking, and the control unit has an output stage for controlling the MOSFET as a function of the additional control signal and the control signal. An alternative embodiment of the control arrangement according to the invention provides that the monitoring unit is designed to inform the control unit via an additional control signal whether the body diode is electrically conductive or blocking, and the control unit has a first output stage for controlling the MOSFET as a function of the control signal in the event that the body diode is electrically blocking, and a second output stage for controlling the MOSFET as a function of the additional control signal in the event that the body diode is electrically conductive.

[0019] A control arrangement according to the invention enables the implementation of the method according to the invention. The advantages of a control arrangement according to the invention therefore correspond to the advantages of the method according to the invention already mentioned above and are not listed separately here.

[0020] Overall, the invention modifies the control of a MOSFET only after the occurrence of a fault that has led to the shutdown of all MOSFETs in the power converter, provided the body diode is electrically conductive. For this purpose, a control arrangement is used that extends the conventional control with the additional function of turning on the MOSFET after the occurrence of the fault if the body diode is electrically conductive. Apart from this, the conventional control of the MOSFET and the conventional protection concept remain unaffected by the invention.

[0021] A power converter according to the invention, in particular a traction power converter, comprises a plurality of MOSFETs, in particular a plurality of MOSFETs each based on a wide bandgap semiconductor, and a control arrangement according to the invention for each MOSFET for controlling the MOSFET. The invention is particularly suitable for controlling a MOSFET of a traction power converter, since current loads on a MOSFET of a traction power converter, especially due to reverse currents, can be very high and can therefore cause high losses.

[0022] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of exemplary embodiments, which are explained in more detail in conjunction with the drawings. FIG 1 shows a circuit diagram of a MOSFET, FIG 2 shows a circuit diagram of a MOSFET and a first exemplary embodiment of a control arrangement for controlling the MOSFET, FIG 3 shows an additional control signal as a function of a drain-source voltage of a MOSFET, FIG 4 shows a circuit diagram of a power converter, FIG 5 shows a flow diagram of a method for controlling a MOSFET.

[0023] Corresponding parts are provided with the same reference numerals in the figures.

[0024] FIG 1 shows a circuit diagram of a MOSFET 1 with a drain terminal D, a source terminal S, a gate terminal G, and a body diode 2. The MOSFET 1 is designed as a normally-blocking n-channel MOSFET based on a wide-bandgap semiconductor, for example, silicon carbide or gallium nitride. Reverse currents, i.e., currents directed (according to the technical current direction) from the source terminal S to the drain terminal D, flow through the body diode 2 when the MOSFET 1 is off.

[0025] FIG 2 shows a circuit diagram of a FIG 1 formed MOSFET 1 and a first embodiment of a control arrangement 3 according to the invention for controlling the MOSFET 1.

[0026] The control arrangement 3 comprises a monitoring unit 5 and a control unit 7. The monitoring unit 5 is designed to determine whether the body diode 2 of the MOSFET 1 is electrically conductive or blocking and to communicate this to the control unit 7. For this purpose, the monitoring unit 5 detects a drain-source voltage U between the drain terminal D and the source terminal S of the MOSFET 1 and outputs a binary additional control signal S2 to the control unit 7, which is dependent on the drain-source voltage U and assumes the value 0 or the value 1. The value 1 of the additional control signal S2 signals that the body diode 2 is electrically conductive. The value 0 of the additional control signal S2 signals that the body diode 2 is electrically blocking.

[0027] FIG 3 shows the additional control signal S2 output by the monitoring unit 5 as a function of the drain-source voltage U. The additional control signal S2 assumes the value 1 when the drain-source voltage U falls below a predetermined first voltage threshold U1. The additional control signal S2 assumes the value 0 when the drain-source voltage U exceeds a predetermined second voltage threshold U2. Both voltage thresholds U1, U2 are negative, with the second voltage threshold U2 being greater than the first voltage threshold U1. For example, the first voltage threshold U1 has a value of approximately -1 V and the second voltage threshold U2 has a value of approximately -0.5 V. At values ​​of the drain-source voltage U that lie between the two voltage thresholds U1, U2, the additional control signal S2 is not changed, i.e., it retains its current value.

[0028] The MOSFET 1 is arranged in a power converter 19, which has several MOSFET 1 (see also FIG 4 ). The control unit 7 controls the MOSFET 1 as a function of a binary control signal S1, which assumes the value 0 or the value 1, and after the occurrence of a fault that has led to all MOSFETs 1 of the power converter 19 being switched off, additionally as a function of the additional control signal S2. For this purpose, the control unit 7 has an OR gate 9 and an output stage 11. The control signal S1 and the additional control signal S2 are fed to the OR gate 9. The OR gate 9 outputs the value 0 to the output stage 11 if both the control signal S1 and the additional control signal S2 assume the value 0. Otherwise, the OR gate 9 outputs the value 1 to the output stage 11. When the OR gate 9 outputs the value 1, the output stage 11 turns on the MOSFET 1 by applying a positive turn-on voltage between the gate terminal G and the source terminal S of the MOSFET 1.Otherwise, the output stage 11 switches off the MOSFET 1 by applying a turn-off voltage between the gate terminal G and the source terminal S of the MOSFET 1.

[0029] FIG 4 shows a circuit diagram of a power converter 19 with a MOSFET 1 and a second embodiment of a control arrangement 3 according to the invention for controlling the MOSFET 1. The power converter 19 is, for example, a traction power converter with further MOSFETs 1 (not shown here), which are connected in a known manner to form half or full bridges, and a further control arrangement 3 for each further MOSFET 1.

[0030] The control arrangements 3 of this embodiment differ from that in FIG 2 shown embodiment merely by the design of the control units 7. A control unit 7 of this embodiment has two output stages 11, 13 and a switch 15. A control signal S1 is supplied to a first output stage 11. After the occurrence of a fault which has led to all MOSFETs 1 of the power converter 19 being switched off, the additional control signal S2 output by the monitoring unit 5 of the respective control arrangement 3 is supplied to the second output stage 13. The switch 15 separates an output of the first output stage 11 from the gate terminal G of the MOSFET 1 controlled by the control arrangement 3 when the additional control signal S2 assumes the value 1. In this case, the MOSFET 1 is switched on by the second output stage 13 in that the second output stage 13 applies a positive switch-on voltage between the gate terminal G and the source terminal S of the MOSFET 1.When the additional control signal S2 assumes the value 0, the output of the first output stage 11 is connected by the switch 15 to the gate terminal G of the MOSFET 1 controlled by the control arrangement 3 and the MOSFET 1 is controlled by the first output stage 11, i.e. no voltage is applied by the second output stage 13 between the gate terminal G and the source terminal S of the MOSFET 1 and the MOSFET 1 is switched on by the first output stage 11 when the control signal S1 assumes the value 1 and switched off when the control signal S1 assumes the value 0.

[0031] The control signals S1 for the MOSFET 1 of the power converter 19 are generated by a controller 17 of the power converter 19. It can be provided that the control of the MOSFET 1 is activated by the second output stages 13 as a function of the additional control signals S2 only when the controller 17 gives the necessary authorization.

[0032] FIG 5 shows a flow diagram of an embodiment of the method according to the invention for controlling a MOSFET 1 with a FIG 2 or FIG 4 executed control arrangement 3.

[0033] In a first method step 21, the voltage threshold values ​​U1, U2 for the drain-source voltage U are specified.

[0034] In a second method step 22, the drain-source voltage U is detected by the monitoring unit 5 and the additional control signal S2 is generated as a function of the drain-source voltage U in the manner described above with reference to FIG 3 described manner and output to the control unit 7.

[0035] In a third method step 23, the MOSFET 1 is switched on by the control unit 7 after the occurrence of a fault which has led to all MOSFETs 1 of the power converter 19 being switched off, i.e. a switch-on voltage is applied between the gate terminal G and the source terminal S of the MOSFET 1 if the additional control signal S2 assumes the value 1. Otherwise, the MOSFET 1 is controlled by the control unit 7 as a function of the control signal S1, i.e. the switch-on voltage is applied between the gate terminal G and the source terminal S of the MOSFET 1 if the control signal S1 assumes the value 1, or a switch-off voltage is applied between the gate terminal G and the source terminal S of the MOSFET 1 if the control signal S1 assumes the value 0. After the third method step 23, the method continues with the second method step 22.

[0036] The exemplary embodiments of a control arrangement 3 according to the invention and of the method according to the invention described above with reference to the figures can be modified in various ways to form alternative exemplary embodiments. In particular, the monitoring unit 5 can be designed in a different way than in the exemplary embodiments described above with reference to the figures.

[0037] For example, the monitoring unit 5 can be designed to detect and evaluate a drain-source current of a drain-source current flowing in a forward direction of the body diode 2 between the drain terminal D and the source terminal S instead of the drain-source voltage U. In this case, a first current threshold for the drain-source current and a second current threshold for the drain-source current, which is smaller than the first current threshold, are specified. The additional control signal S2 is set to the value 1 if the drain-source current exceeds the first current threshold. The additional control signal S2 is set to the value 0 if the drain-source current falls below the first current threshold. For drain-source current values ​​that lie between the two current thresholds, the additional control signal S2 is not changed, i.e., it retains its current value.The drain-source current is measured, for example, with a shunt resistor arranged in the current path of the drain-source current.

[0038] Alternatively, the monitoring unit 5 can be configured to detect a direction of the drain-source current. In this case, the additional control signal S2 is set to the value 1 if the drain-source current flows in the forward direction of the body diode 2. Otherwise, the additional control signal S2 is set to the value 0. For example, the direction of the drain-source current is determined using a ferromagnetic core that triggers a voltage pulse each time the direction of the drain-source current changes. The direction of the drain-source current is determined, for example, by counting the triggered voltage pulses or by a flip-flop that changes its state with each triggered voltage pulse.

[0039] To FIG 4 Alternative embodiments of a power converter 19 are obtained by replacing the FIG 4 shown control arrangement 3 by a control arrangement 3 of the embodiment described in Figure 2 or one of the aforementioned modified embodiments.

[0040] Although the invention has been illustrated and described in detail by means of preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the claims.

Claims

1. Method for actuating a MOSFET (1), in particular a MOSFET (1) based on a semiconductor with a wide bandgap, a converter (19) having a number of MOSFETs (1), wherein after the occurrence of a fault, which has resulted in all MOSFETs (1) of the converter (19) switching off, - it is monitored whether the body diode (2) of the MOSFET (1) is electrically conducting, - the MOSFET (1) is switched on if the body diode (2) is electrically conducting, and - the MOSFET (1) is actuated as a function of an actuation signal (S1) if the body diode (2) is electrically conducting, - wherein a drain-source voltage (U) is detected between the drain terminal (D) and the source terminal (S) of the MOSFET (1), characterised in that - a first voltage threshold value (U1) is predetermined for the drain-source voltage (U) and it is concluded therefrom that the body diode (2) is electrically conducting when the drain-source voltage (U) fails to reach the first voltage threshold value (U1), - a second voltage threshold value (U2) is predetermined for the drain-source voltage (U) and it is concluded therefrom that the body diode (2) is electrically blocking when the drain-source voltage (U) exceeds the second voltage threshold value (U2), - the direction of a drain-source current flowing between the drain terminal (D) and the source terminal (S) of the MOSFET (1) is detected and it is concluded therefrom that the body diode (2) is electrically conducting when the drain-source current flows in a forward direction of the body diode (2), - it is concluded therefrom that the body diode (2) is electrically blocking when the drain-source current flows opposite to the forward direction of the body diode (2), - in a first method step (21) the voltage threshold values (U1, U2) are predetermined for the drain-source voltage (U), wherein in a second method step (22) a monitoring unit (5) detects the drain-source voltage (U) and forms an additional actuation signal (S2) as a function of the drain-source voltage (U) and outputs the same to a control unit (7) and wherein in a third method step (23), the MOSFET (1) is switched on by the control unit (7) after the occurrence of a fault, which has resulted in all MOSFETs (1) of the converter (19) switching off, and - a switch-on voltage is applied between the gate terminal (G) and the source terminal (S) of the MOSFET (1) when the additional actuation signal (S2) assumes the value 1, wherein the value 1 of the additional actuation signal (S2) signals that the body diode (2) is electrically conducting and wherein the value 1 of the additional actuation signal (S2) signals that the body diode (2) is electrically conducting, and otherwise, the MOSFET (1) is actuated by the control unit (7) as a function of the actuation signal (S1), wherein the switch-on voltage is applied between the gate terminal (G) and the source terminal (S) of the MOSFET (1) when the actuation signal (S1) assumes the value 1, or a switch-off voltage is applied between the gate terminal (G) and the source terminal (S) of the MOSFET (1) when the actuation signal (S1) assumes the value 0, wherein after the third method step (23), the method is continued with the second method step (22).

2. Method according to claim 1, wherein both voltage threshold values (U1, U2) are negative, wherein the second voltage threshold value (U2) is greater than the first voltage threshold value (U1).

3. Method according to one of the preceding claims, wherein a first current threshold value is predetermined for a drain-source current intensity of a drain-source current flowing in a forward direction of the body diode (2) between the drain terminal (D) and the source terminal (S) of the MOSFET (1), the drain-source current intensity is detected and it is concluded therefrom that the body diode (2) is electrically conducting if the drain-source current intensity exceeds the first voltage threshold value.

4. Method according to claim 3, wherein a second current threshold value is predetermined for the drain-source current intensity, which is smaller than the first current threshold value, and it is concluded therefrom that the body diode (2) is electrically blocking if the drain-source current intensity does not reach the second current threshold value.

5. Actuation arrangement (3) which is embodied to carry out the method according to one of the preceding claims, the actuation arrangement (3) comprising - a monitoring unit (5), which is embodied to determine whether the body diode (2) is electrically conducting or blocking, and - a control unit (7), which is embodied, after the occurrence of a fault, which has resulted in all MOSFETs (1) of the converter (19) switching off, to switch on the MOSFET (1) if the monitoring unit (5) determines that the body diode (2) is electrically conducting, and to actuate the MOSFET (1) as a function of the actuation signal (S1) if the body diode (2) is electrically blocking, - wherein the monitoring unit (5) is embodied to detect the drain-source voltage (U) and to determine on the basis of the drain-source voltage (U) whether the body diode (2) is electrically conducting or blocking, - wherein the monitoring unit (5) is embodied to detect the drain-source current intensity and on the basis of the drain-source current intensity to determine whether the body diode (2) is electrically conducting or blocking and - wherein the monitoring unit (5) is embodied to detect the direction of the drain-source current and on the basis of the direction of the drain-source current to determine whether the body diode (2) is electrically conducting or blocking, and - wherein the monitoring unit (5) is embodied to communicate to the control unit (7) by means of an additional actuation signal (S2) whether the body diode (2) is electrically conducting or blocking, and wherein the control unit (7) has an end stage (11) for actuating the MOSFET (1) as a function of the additional actuation signal (S2) and the actuation signal (S1)) or wherein the monitoring unit (5) is embodied to communicate to the control until (7) by means of an additional actuation signal (S2) whether the body diode (2) is electrically conducting or blocking, and wherein the control unit (7) has a first end stage (11) for actuating the MOSFET (1) as a function of the actuation signal (S1) in the event that the body diode (2) is electrically blocking, and a second end stage (13) for actuating the MOSFET (1) as a function of the additional actuation signal (S2) in the event that the body diode (2) is electrically conducting.

6. Converter (19) with a number of MOSFETs (1), wherein the converter (19) for each MOSFET (1) has an actuation arrangement (3), embodied according to one of the preceding claims, for actuating the MOSFET (1).

7. Converter (19) according to claim 6, wherein the converter (19) is a traction converter.