Control of Metal Oxide Semiconductor Field Effect Transistors

Abstract

The invention relates to a control device (3) and a method for controlling a MOSFET (1), in particular a MOSFET (1) based on a semiconductor with a wide bandgap. According to the invention, a characteristic block is created in which a change (ΔU1, ΔU2, ΔR1, ΔR2) of at least one control variable (U1, U2, R1, R2) for controlling the MOSFET (1) relative to a reference control value of the control variable (U1, U2, R1, R2) is stored in relation to at least one operating characteristic variable (U, T) influencing the switching characteristic of the MOSFET (1), the change counteracting a change in the switching characteristic caused by the at least one operating characteristic variable (U, T). During operation of the MOSFET (1), an actual value of the at least one operating characteristic variable (U, T) is determined, and according to the characteristic block, the at least one control variable (U1, U2, R1, R2) is changed relative to the reference control value of the at least one control variable in relation to the actual value of the at least one operating characteristic variable (U, T).

Description

Technical Field

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

[0002] The switching behavior of a MOSFET is strongly dependent on the operating conditions under which the MOSFET is operated, in particular on the operating voltage and the operating temperature of the MOSFET between the drain and the source in the MOSFET off state. For the use of MOSFETs, predictable and constant MOSFET switching behavior is required in order to comply with boundary conditions, such as for overvoltages when the MOSFET is switched off and for electromagnetic compatibility. Especially in applications with strongly fluctuating operating conditions, MOSFETs based on semiconductors with wide band gaps are currently increasingly used, such as in traction converters, in which the operating voltage can fluctuate strongly.

[0003] US 2017 / 0155250 A1 discloses a method and a device for controlling an electrical or electronic switching element, wherein a PWM signal for controlling the switching element is modulated as a function of a supply voltage and / or an ambient temperature of the switching element.

[0004] US2017 / 0021733A1 discloses a device for controlling multiple switching elements of a converter, which is configured to reduce the switching speed of each switching element when the atmospheric pressure drops, the ambient temperature drops and / or the input voltage increases. Summary of the invention

[0005] The object of the present invention is to provide a control device and a method for controlling a MOSFET, which control device and method improve the stability of the switching behavior of the MOSFET under changing operating conditions.

[0006] According to the invention, the object is achieved by a method having the features of the invention and by a control device having the features of the invention.

[0007] Advantageous embodiments of the invention are the subject matter of the individual exemplary embodiments.

[0008] In the method according to the invention for driving a MOSFET, in particular a MOSFET based on a semiconductor with a wide bandgap, a characteristic block is created in which a change of at least one drive variable for driving the MOSFET relative to a reference drive value of the drive variable is stored in relation to at least one operating characteristic variable influencing the switching characteristic of the MOSFET, the change counteracting the change in the switching characteristic caused by the at least one operating characteristic variable. During the operation of the MOSFET, an actual value of the at least one operating characteristic variable is determined, and according to the characteristic block, the at least one drive variable is changed relative to its reference drive value in relation to the actual value of the at least one operating characteristic variable.

[0009] The present invention utilizes that the dependence of the switching characteristic of the MOSFET on the operating characteristic variable that influences the switching characteristic can be depicted very accurately by a characteristic curve, and the characteristic curve describes the driving variable used to drive the MOSFET according to the operating characteristic variable. The present invention proposes to create a characteristic block, which has one or more characteristic curves, and the characteristic curves respectively indicate the change of the driving variable relative to the reference driving value in relation to at least one operating characteristic variable, which is necessary in order to counteract the change of the switching characteristic caused by the at least one operating characteristic variable. According to the characteristic block, the driving variable related to the actual value of the at least one operating characteristic variable is adjusted. In this way, the influence of the at least one operating characteristic value variable on the switching characteristic of the MOSFET can be compensated, so that the switching characteristic of the MOSFET is stabilized.

[0010] The design of the present invention proposes that: in the feature block, changes in the on-drive control voltage for turning on the MOSFET, changes in the off-drive control voltage for turning off the MOSFET, changes in the on-gate resistance for turning on the MOSFET, and / or changes in the off-gate resistance for turning off the MOSFET are stored in association with at least one operating characteristic variable. In other words, the design of the present invention sets the on-drive control voltage, the off-drive control voltage, the on-gate resistance, and / or the off-gate resistance for the MOSFET as control variables, respectively, and changes in the control variables are stored in the feature block in association with at least one operating characteristic variable. The design of the present invention advantageously enables the gate-source voltage of the MOSFET used to turn on and / or turn off the MOSFET to be directly affected in association with at least one operating characteristic variable.

[0011] Another design of the present invention proposes that the change of at least one control variable is stored in the characteristic block in dependence on the operating voltage and / or operating temperature of the MOSFET. This design of the present invention takes into account that the switching characteristics of the MOSFET are mainly related to the operating voltage and the operating temperature, and therefore the switching characteristics of the MOSFET are stabilized mainly by compensating for the influence of these two operating characteristic variables.

[0012] The control device according to the present invention for executing the method according to the present invention comprises: an evaluation unit, which is designed to store a characteristic block and to determine a change in at least one control variable based on the characteristic block in relation to an actual value of at least one operating characteristic variable; and a control unit, which is designed to control the MOSFET based on a control signal having a control value of at least one control variable, and to change the control value relative to a reference control value of the control variable based on the change determined by the evaluation unit.

[0013] According to the design of the drive control device of the present invention, the control unit has: a controllable on-voltage source for generating a variable on-drive voltage for turning on the MOSFET; a controllable off-voltage source for generating a variable off-drive voltage for turning off the MOSFET; a controllable on-resistance unit for generating a variable on-gate resistance for turning on the MOSFET; and / or a controllable off-resistance unit for generating a variable off-gate resistance for turning off the MOSFET.

[0014] According to another embodiment of the invention, a measuring device is provided for detecting the actual value of at least one operating characteristic variable, the influence of which on the switching characteristic of the MOSFET is taken into account in the characteristic block. For example, the measuring device is designed to detect the actual value of the operating voltage and / or operating temperature of the MOSFET.

[0015] The control device according to the invention is able to carry out the method according to the invention. The advantages of the control device according to the invention therefore correspond to the advantages already mentioned above of the method according to the invention and are not described separately here.

[0016] The converter according to the invention, in particular a traction converter, comprises at least one MOSFET, in particular a MOSFET based on a semiconductor with a wide bandgap, and a control device according to the invention for controlling the MOSFET. The invention is particularly suitable for controlling the MOSFET of a traction converter, since the operating voltage of the traction converter can fluctuate greatly and thus change the switching characteristics of the MOSFET. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above-described characteristics, features and advantages of the present invention and the manner and method of achieving them are explained in more detail with reference to the accompanying drawings and in combination with the following schematic description of the embodiments.

[0018] Figure 1 A first embodiment of a driving device for driving a MOSFET and a circuit diagram of the MOSFET are shown,

[0019] Figure 2 A circuit diagram of a control unit for driving a MOSFET is shown.

[0020] Figure 3 The characteristic curve showing the change in the on-state control voltage as a function of the operating voltage of the MOSFET,

[0021] Figure 4 The circuit diagram of the converter is shown,

[0022] Figure 5 A flow chart of a method for driving a MOSFET is shown.

[0023] In the figures, components that correspond to one another are provided with the same reference symbols. DETAILED DESCRIPTION

[0024] Figure 1 A first exemplary embodiment of a control device 3 for controlling a MOSFET 1 and a circuit diagram of the MOSFET 1 are shown.

[0025] The MOSFET 1 is designed as a normally-blocking n-channel MOSFET based on a semiconductor with a wide bandgap (eg silicon carbide or gallium nitride).

[0026] The control device 3 comprises a control unit 5 , an evaluation unit 7 and a measuring device 9 .

[0027] The measuring device 9 is designed to detect an operating temperature T and an operating voltage U of the MOSFET 1 as operating variables T, U. The measuring device 9 has a temperature sensor 11, such as an NTC resistor (negative temperature coefficient thermistor), in order to detect the operating temperature T. The operating voltage U is measured, for example, as a drain-source voltage between the drain D and the source S of the MOSFET 1 in the off state of the MOSFET 1.

[0028] Figure 2 The circuit diagram of the control unit 5 is schematically shown. The control unit 5 comprises a controllable on-voltage source 13 for generating a variable on-control voltage U1 for switching on the MOSFET 1, a controllable off-voltage source 15 for generating a variable off-control voltage U2 for switching off the MOSFET 1, a controllable on-resistance unit R1 for generating a variable on-gate resistance R1 for switching on the MOSFET 1, a controllable off-resistance unit R2 for generating a variable off-gate resistance R2 for switching off the MOSFET 1, a first terminal 21 connected to the gate G of the MOSFET 1, and a second terminal 23 connected to the source S of the MOSFET 1. The on-resistance unit 17 and the off-resistance unit 19 each have, for example, a plurality of individual resistors, wherein the number of individual resistors required for setting a specific on-gate resistance R1 or off-gate resistance R2 can be connected to each other in circuit.

[0029] The first pole of the switch-on voltage source 13 and the first pole of the switch-off voltage source 15 are respectively permanently connected to the second terminal 23. To switch on the MOSFET 1, the second pole of the switch-on voltage source 13 is connected to the first terminal 21 via the switch-on resistor unit 17 by closing the first switch 25, and the second pole of the switch-off voltage source 15 is disconnected from the switch-off resistor unit 19 and the first terminal 21 by opening the second switch 27. To switch off the MOSFET 1, the second pole of the switch-off voltage source 15 is connected to the first terminal 21 via the switch-off resistor unit 19 by closing the second switch 27, and the switch-on voltage source 13 is disconnected from the switch-on resistor unit 17 and the first terminal 21 by opening the first switch 25. The switching on and off of the MOSFET 1 is controlled by the binary control signal 12 supplied to the control unit 5.

[0030] The switch-on control voltage U1 for switching on the MOSFET 1 and the switch-on gate resistor R1 for switching on the MOSFET 1, as well as the switch-off control voltage U2 for switching off the MOSFET 1 and the switch-off gate resistor R2 for switching off the MOSFET 1 are control variables U1, U2, R1, R2 for controlling the MOSFET 1, which are set in accordance with the operating voltage U and the operating temperature T of the MOSFET 1. For this purpose, a characteristic block is stored in the evaluation unit 7, in which changes ΔU1, ΔU2, ΔR1, ΔR2 of the control variables U1, U2, R1, R2, respectively, relative to reference control values ​​are stored in relation to the operating temperature T and the operating voltage U, which counteract changes in the switching behavior of the MOSFET 1 caused by the operating temperature T or the operating voltage U.

[0031] The evaluation unit 7 determines the changes ΔU1, ΔU2, ΔR1, ΔR2 of the control variables U1, U2, R1, R2 relative to the corresponding reference control values ​​for the operating temperature T and the operating voltage U detected by the measuring device 9 according to the characteristic block, and transmits the changes ΔU1, ΔU2, ΔR1, ΔR2 to the control unit 5. The control unit 5 sets the switch-on control voltage U1, the switch-off control voltage U2, the switch-on gate resistor R1, and the switch-off gate resistor R2 to control values ​​that have changed relative to the reference control values.

[0032] Figure 3 The characteristic curve of a characteristic block of a change ΔU1 of the switch control voltage U1 in relation to a reference control value of the switch control voltage U1 as a function of the operating voltage U is shown by way of example. The value ΔU1 obtained from the characteristic curve of the operating voltage U is added to the reference control value of the switch control voltage U1.

[0033] Figure 4The circuit diagram of a converter 30 with a MOSFET 1 and a second exemplary embodiment of a control device 3 according to the invention for controlling the MOSFET 1 is shown. The converter 30 is, for example, a traction converter with further MOSFETs 1 (not shown here) and further control devices 3 for each further MOSFET 1, which are connected in a known manner to form a full bridge or a half bridge. The control devices 3 of this exemplary embodiment are connected to the control device 3 of the embodiment. Figure 1 The embodiment of the ...

[0034] Figure 5 Shown for use according to Figure 1 or Figure 4 A flow chart of an exemplary embodiment of a method according to the present invention for controlling a MOSFET 1 by a control device 3 is shown.

[0035] In a first method step S1, a feature block is created in which a change ΔU1 of the switch-on control voltage U1, a change ΔU2 of the switch-off control voltage U2, a change ΔR1 of the switch-on gate resistor R1, and a change ΔR2 of the switch-off gate resistor R2 are stored, respectively, as a function of the operating temperature T and the operating voltage U of the MOSFET 1. The feature block is stored in an evaluation unit 7 of the control device 3.

[0036] In a second method step S2 , the current operating temperature T and the current operating voltage U of the MOSFET 1 (ie, the actual values ​​of the operating temperature T and the operating voltage U) are determined and supplied to the evaluation unit 7 .

[0037] In the third method step S3 , the evaluation unit 7 determines the changes ΔU1, ΔU2, ΔR1, ΔR2 of the switch-on control voltage U1, switch-off control voltage U2, switch-on gate resistance R1 and switch-off gate resistance R2 relative to their corresponding reference control values ​​based on the characteristic block for the values ​​of the operating temperature T and the operating voltage U determined in the second method step S2 and transmits them to the control unit 5 .

[0038] In a fourth method step S4, the control unit 5 sets the switch-on control voltage U1, the switch-off control voltage U2, the switch-on gate resistor R1 and the switch-off gate resistor R2 to control values ​​which are changed relative to the corresponding reference control values ​​by adding the changes ΔU1, ΔU2, ΔR1, ΔR2 determined in the third method step S3 to the reference control values. After the fourth method step S4, the method continues with method step S2.

[0039] The exemplary embodiments of the control device 3 according to the invention and the method according to the invention described above with reference to the figures can be transformed into alternative exemplary embodiments in different ways. For example, the changes ΔU1, ΔU2, ΔR1, ΔR2 of the switch-on control voltage U1, the switch-off control voltage U2, the switch-on gate resistor R1 and the switch-off gate resistor R2 relative to the corresponding reference control values ​​are determined and set only as a function of the operating temperature T or only as a function of the operating voltage U instead of being determined and set as a function of the operating temperature T and the operating voltage U. In addition, it can be provided that only the changes ΔU1, ΔU2, ΔR1, ΔR2 of a subset of the control variables U1, U2, R1, R2 relative to the corresponding reference control values ​​are determined and set as a function of the operating temperature T and / or the operating voltage U, for example only the changes ΔU1, ΔU2 of the switch-on control voltage U1 and the switch-off control voltage U2 or the changes ΔR1, ΔR2 of the switch-on gate resistor R1 and the switch-off gate resistor R2 are determined and set. In addition, taking into account the operating temperature T, it can be proposed that the current operating temperature T of MOSFET 1 be calculated based on the temperature-related electrical parameters of MOSFET 1, for example, as described in "IGBT Gate Driver with Accurate Measurement of Junction Temperature and Inverter Output Current" by M. Denk and M. M. Bakran, PCIM Europe 2017; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, Nuremberg, Germany, 2017, pages 1-8, or the current operating temperature T be determined with the help of a model that estimates the operating temperature T using other operating conditions.

[0040] The converter 19 is replaced by Figure 4 The embodiment of Figure 1 The control device 3 of the embodiment described in the embodiment or one of the modified embodiments described above is replaced by Figure 4 The control device 3 shown in FIG.

[0041] Although the details of the present invention have been illustrated and described in detail through preferred embodiments, the present invention is not limited to the disclosed examples and a person skilled in the art can derive other variants therefrom without departing from the scope of protection of the present invention.

Claims

1. A method for driving a MOSFET (1), wherein: - creating a characteristic block in which a change of at least one control variable for controlling the MOSFET (1) relative to a reference control value of the control variable is stored in relation to at least one operating characteristic variable influencing the switching characteristic of the MOSFET (1), the change counteracting a change of the switching characteristic caused by the at least one operating characteristic variable, the characteristic block having a characteristic curve which displays a change of the control variable relative to the reference control value in relation to the at least one operating characteristic variable, - determining an actual value of at least one of the operating characteristic variables during operation of the MOSFET (1), and - according to the characteristic block, at least one of the controlled variables is changed relative to a reference controlled value of the at least one controlled variable as a function of the actual value of at least one of the operating characteristic variables.

2. The method according to claim 1, wherein: The MOSFET (1) is a MOSFET (1) based on a semiconductor having a wide bandgap.

3. The method according to claim 1 or 2, wherein: In the characteristic block, a change in a switch-on control voltage (U1) for switching on the MOSFET (1) is stored as a function of at least one of the operating characteristic variables.

4. The method according to claim 1 or 2, wherein: In the characteristic block, a change in a turn-off control voltage (U2) for turning off the MOSFET (1) is stored as a function of at least one of the operating characteristic variables.

5. The method according to claim 1 or 2, wherein: In the characteristic block, a change in a switch-on gate resistor (R1) for switching on the MOSFET (1) is stored as a function of at least one of the operating characteristic variables.

6. The method according to claim 1 or 2, wherein: In the characteristic block, a change in a turn-off gate resistor (R2) for turning off the MOSFET (1) is stored in relation to at least one of the operating characteristic variables.

7. The method according to claim 1 or 2, wherein: In the characteristic block, a change in at least one of the control variables is stored as a function of an operating voltage (U) of the MOSFET (1).

8. The method according to claim 1 or 2, wherein: In the characteristic block, a change in at least one of the control variables is stored as a function of an operating temperature (T) of the MOSFET (1).

9. A control device for executing the method according to any one of claims 1 to 8, the control device comprising: - an evaluation unit (7) which is designed to store the characteristic block and to determine a change in at least one of the control variables based on the characteristic block in dependence on an actual value of at least one of the operating characteristic variables; and - a control unit (5) designed to control the MOSFET (1) as a function of a control signal (12) having a control value of at least one of the control variables, the control value being varied relative to the reference control value of the control variable as a function of the change determined by the evaluation unit (7).

10. The driving control device according to claim 9, wherein: The control unit (5) has a controllable switch-on voltage source (13) for generating a variable switch-on control voltage (U1) for switching on the MOSFET (1).

11. The driving control device according to claim 9 or 10, wherein: The control unit (5) has a controllable disconnection voltage source (15) for generating a variable disconnection control voltage (U2) for disconnecting the MOSFET (1).

12. The driving control device according to claim 9 or 10, wherein: The control unit (5) has a controllable on-resistance unit for generating a variable on-gate resistance (R1) for switching on the MOSFET (1).

13. The driving control device according to claim 9 or 10, wherein: The control unit (5) has a controllable turn-off resistor unit for generating a variable turn-off gate resistor (R2) for turning off the MOSFET (1).

14. The control device according to claim 9, comprising a measuring device (9) for detecting an actual value of at least one operating characteristic variable, the influence of the actual value on the switching behavior of the MOSFET (1) being taken into account in the characteristic block.

15. The driving control device according to claim 14, wherein: The measuring device (9) is designed to detect an actual value of an operating voltage (U) and / or an actual value of an operating temperature (T) of the MOSFET (1).

16. A converter (30) comprising at least one MOSFET (1) and a control device according to any one of claims 9 to 15 for controlling the MOSFET (1).

17. The converter (30) according to claim 16, wherein: The converter (30) is a traction converter.

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