Switching device for a power electronics module with damping function for voltage transients caused by switch-on speed

Abstract

The invention relates to a switching device (1) for a power electronics module of a motor vehicle, having: - at least one switching unit (2a, 2b) comprising at least one semiconductor switch (3a, 3b), - a driver circuit (4) connected to a control terminal (G) of the at least one semiconductor switch (3a, 3b), which is designed to provide a charging path for charging the control terminal (G) of the at least one semiconductor switch (3a, 3b) for a switch-on process of the associated switching unit (2a, 2b), and a discharging path for discharging the control terminal (G) of the at least one semiconductor switch (3a, 3b) for a switch-off process of the associated switching unit (2a, 3b), characterised in that the driver circuit (4) for damping voltage transients (8a, 8b) of an output voltage (U) of the switching device (1) caused by switch-on speed is designed to temporarily provide the discharge path for at least one semiconductor switch (3a, 3b) of the switching unit (2a, 2b) during a switch-on process of the at least one switching unit (2a, 2b).

Description

[0001] Switching device for a power electronics module with damping function for switch-on speed-related voltage transients

[0002] The invention relates to a switching device for a power electronics module of a motor vehicle, which has at least one switching unit with at least one semiconductor switch and a driver circuit connected to a control terminal of the at least one semiconductor switch. The driver circuit is designed to provide a charging path for charging the control terminal of the at least one semiconductor switch for a switch-on operation of the associated switching unit and a discharging path for discharging the control terminal of the at least one semiconductor switch for a switch-off operation of the associated switching unit. The invention also relates to a power electronics module, a motor vehicle, and a method for operating a switching unit of a switching device.

[0003] In this case, interest is focused on power electronics modules for motor vehicles, in particular electrified motor vehicles. Such power electronics modules include, for example, power converters such as inverters and on-board chargers, which have electronic switches or semiconductor switches to convert one type of current into another. Such semiconductor switches can, for example, be transistors with a semiconductor material with a wide band gap, the advantages of which lie particularly in steep switching edges and thus fast switching speeds. These steep switching edges can minimize switching losses in the linear range in which the transistor is during a switching process. In order to be able to switch between an on state and an off state of the transistor with the steepest possible edge, a driver circuit which is connected to a control terminal orThe transistor's gate terminal is connected to the gate terminal of the transistor, and must provide a specific gate charging current in order to provide the necessary gate charge as quickly as possible. For this purpose, gate series resistors and gate inductors are generally designed to be as small as possible. However, high turn-on speeds lead to undesired voltage transients such as voltage spikes ("overshoot") and oscillations ("ringing") due to overexcitation, which reduce switching efficiency. For this purpose, it is known from the prior art to use damping devices, so-called snubbers. Such damping devices have discrete components, for example snubber capacitors, which dampen the undesired voltage transients, but require space in the power electronics module and increase the cost of the power electronics module.

[0004] It is an object of the present invention to provide a simple, cost- and space-saving solution for damping switch-on speed-related voltage transients of switching units of a power electronics module for a motor vehicle.

[0005] This object is achieved according to the invention by a switching device, a power electronics module, a motor vehicle, and a method for switching on a switching unit according to the respective independent patent claims. Advantageous embodiments of the invention are the subject of the dependent patent claims, the description, and the figures.

[0006] A switching device according to the invention for a power electronics module of a motor vehicle has at least one switching unit with at least one semiconductor switch and a driver circuit connected to a control terminal of the at least one semiconductor switch. The driver circuit is designed to provide a charging path for charging the control terminal of the at least one semiconductor switch for a switch-on process of the associated switching unit and a discharging path for discharging the control terminal of the at least one semiconductor switch for a switch-off process of the associated switching unit. In addition, the driver circuit is designed to dampen switch-on speed-related voltage transients of an output voltage of the switching device by temporarily providing the discharge path for at least one semiconductor switch of the switching unit during a switch-on process of the switching unit.

[0007] The invention also relates to a power electronics module for a motor vehicle having at least one switching device according to the invention, as well as to a motor vehicle having a power electronics module according to the invention. The motor vehicle is, in particular, an electrified motor vehicle in the form of an electric or hybrid vehicle. The power electronics module is, for example, a power converter in the form of an inverter, which is connected between a high-voltage energy storage device and an electric drive motor of the motor vehicle and is designed to convert a direct current provided by the high-voltage energy storage device into a multiphase alternating current for the electric drive motor.The power electronics module can also be a power converter in the form of an on-board charger, which is connected between the high-voltage energy storage device and a charging connection of the motor vehicle and is designed to convert an alternating current provided by a charging station external to the vehicle into a direct current for charging the high-voltage energy storage device.

[0008] The power electronics module has at least one switching device. The switching device has at least one switching unit. Each switching unit can have a semiconductor switch or a parallel circuit comprising several semiconductor switches to increase the current-carrying capacity. The semiconductor switches are, in particular, power transistors comprising a semiconductor material with a wide band gap, in particular silicon carbide and / or gallium nitride. The power transistors have a control connection in the form of a gate connection, via which the power transistor can be switched between an on-state or conducting state and an off-state or blocking state. The driver circuit, also referred to as a gate driver, is provided for this purpose. The driver circuit has, in particular, a driver component for each power transistor.

[0009] For example, each power transistor can be connected to an output of the driver circuit, with each output connected to a driver chip. Furthermore, the power transistors have output terminals, such as a source terminal and a drain terminal, through which a current flows in the conducting state and no current flows in the off state.

[0010] The gate terminal of the semiconductor switch forms a capacitor, a so-called gate capacitance, which is charged to turn the semiconductor switch on and discharged to turn it off. To turn the semiconductor switch on, the driver circuit thus provides the charging path, via which charge is supplied to the control terminal in the form of a charging current. To turn the semiconductor switch off, the driver circuit provides the discharging path, via which charge is removed from the control terminal in the form of a discharging current. In other words, a charging current flows to the control terminal to turn it on, and a discharging current flows out of the control terminal to turn it off. The charging current and the discharging current have opposite current directions.

[0011] Steep switching edges during turn-on, i.e., high turn-on speeds, of the semiconductor switch lead to undesirable, efficiency-reducing voltage transients in the form of overvoltage spikes and oscillations in the switching device's output voltage. To dampen these voltage transients, the gate charge of at least one semiconductor switch of the switching unit is transiently modified during the turn-on process, so that this semiconductor switch itself serves as a damping element and provides a snubber effect. To modify the gate charge during the turn-on process of the switching unit, i.e., in the linear range of the at least one semiconductor switch, the discharge path is temporarily provided. In other words, charge is briefly removed from the control terminal of the at least one semiconductor switch before it is fully charged.During this brief charge drain from the gate terminal, the at least one semiconductor switch can dissipate the oscillation energy and thus dampen the voltage transients. Subsequently, charge is supplied to the control terminal to turn on the at least one semiconductor switch and thus turn on the switching unit until the control terminal is fully charged.

[0012] By using at least one already existing semiconductor switch as a damping element, no additional discrete damping components are advantageously required, so that no installation space has to be made available for them in the power electronics module and the costs of the power electronics module are reduced.

[0013] It can be provided that the driver circuit is designed to first provide the charging path for a first period of time, then the discharging path for a second period of time, and finally the charging path again for a third period of time during the switching-on process of the switching unit for the at least one semiconductor switch. According to this embodiment, the charging path and the discharging path are therefore provided at different times. For example, the driver circuit is designed to charge the control terminal to 80% of the maximum charge quantity in the first period of time, discharge 20% in the second period of time, and charge it to 100%, i.e. the maximum charge quantity, in the third period of time. In the case of several semiconductor switches connected in parallel per switching unit, the charging path can be provided first for each semiconductor switch, then the discharging path, and finally the charging path again.Thus, each semiconductor switch of the associated switching unit can achieve the snubber effect.

[0014] With multiple semiconductor switches connected in parallel per switching unit, it can also be provided that the driver circuit is designed to provide the discharge path only for some of the semiconductor switches connected in parallel. For example, for a first group of semiconductor switches, only the respective charging path is provided during the switching unit's turn-on process. For a second group of semiconductor switches, the discharge path is also provided, so that the second group of semiconductor switches provides the snubber effect for the entire switching unit. Charging and discharging paths are thus provided by the driver circuit in parallel.

[0015] It can also be provided that the switching device has a commutation cell with two switching units connected in series, in which the output voltage can be switched between a high-side potential and a low-side potential by switching the switching units. The driver circuit is designed to temporarily provide the discharge path for the respective switching unit to be switched on during a switching process. For example, a first switching unit is connected to a high-side terminal and a center point terminal of the switching device. A second switching unit is connected to the center point terminal and a low-side terminal. The high-side terminal can be electrically connected to a high-side potential and the low-side terminal can be electrically connected to a low-side potential. The center point terminal is connected to the output terminal of the switching device.When the first switching unit is switched on and the second switching unit is switched off, the switching device provides the high-side potential at the output terminal. When the second switching unit is switched on and the first switching unit is switched off, the switching device provides the low-side potential at the output terminal. The driver circuit is designed to provide the discharge path at the respective switching unit to be switched on during the switching operations between the high-side potential and the low-side potential, in order to thereby dampen the voltage transients resulting from the switch-on speed of the respective switching unit being switched on during the switching operations of the switching device.The embodiments presented with reference to the switching device according to the invention and their advantages apply accordingly to the power electronics module according to the invention, to the motor vehicle according to the invention and to the method according to the invention.

[0016] Further features of the invention emerge from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective specified combination, but also in other combinations or on their own.

[0017] The invention will now be explained in more detail using a preferred embodiment and with reference to the drawings. They show:

[0018] Fig. 1 is a schematic representation of a switching device for a power electronics module, and

[0019] Fig. 2 Curves of an output voltage of the switching device and an input current of a semiconductor switch of the switching device.

[0020] In the figures, identical and functionally identical elements are provided with the same reference numerals.

[0021] Fig. 1 shows a switching device 1 for a power electronics module, for example an inverter, of a motor vehicle. The switching device 1 here has two switching units 2a, 2b, each with a semiconductor switch 3a, 3b. The semiconductor switches 3a, 3b are designed, for example, as silicon carbide (SiC) power transistors or gallium nitride (GaN) power transistors. Each of the semiconductor switches 3a, 3b has a control terminal G in the form of a gate terminal. In addition, the semiconductor switches 3a, 3b have output terminals in the form of a source terminal S and a drain terminal D. A first switching unit 2a is connected to a high-side terminal H and a center point terminal M of the switching device 1, a second switching unit 2b is connected to the center point terminal M and a low-side terminal L of the switching device 1.The switching device 1 provides at its output, which corresponds to the center point terminal M, a high-side potential VH applied to the high-side terminal H in the switched-on state of the first semiconductor switch 3a and in the switched-off state of the second semiconductor switch 3b, and a low-side potential VL applied to the low-side terminal L in the switched-off state of the first semiconductor switch 3a and in the switched-on state of the second semiconductor switch 3b.

[0022] To switch on the respective switching unit 2a, 2b, the associated semiconductor switches 3a, 3b are switched on and placed in a conducting state. To switch off the respective switching units 2a, 2b, the associated semiconductor switches 3a, 3b are switched off and placed in a blocking state. To switch the semiconductor switches 3a, 3b on and off, the switching device 1 has a driver circuit 4 with semiconductor switch-specific outputs 5a, 5b, via which each semiconductor switch 3a, 3b can be controlled separately. The driver circuit 4 has a charging path for charging the gate terminal G for a switching-on process and a discharging path for discharging the gate terminal G for a switching-off process of the respective semiconductor switch 3a, 3b.

[0023] Fig. 2 shows curves 6, 7 of an output voltage U of the switching device 1 over time t. The curve 6 of the output voltage U exhibits undesirable voltage transients 8a, 8b, which result from the turn-on speeds of the respective semiconductor switches 3a, 3b being switched on during a switching process between the switching units 2a, 2b. The voltage transients 8a result from the turn-on process of the first semiconductor switch 3a, and the voltage transients 8b result from the turn-on process of the second semiconductor switch 3b. These voltage transients 8a, 8b reduce the switching efficiency of the switching device 1.

[0024] In order to dampen these voltage transients 8a, 8b and maintain the curve 7 of the output voltage U, the driver circuit 4 is designed to temporarily provide the discharge path during the turn-on processes of the associated semiconductor switch 3a, 3b. Fig. 2 shows an example of a curve 9 of the input current I, which the driver circuit 4 provides for the turn-on process of the first semiconductor switch 3a. Here, the gate terminal G of the associated semiconductor switch 3a, 3b is first charged to a value below the maximum gate charge. For example, to turn on the first semiconductor switch 3a, the driver circuit 4 supplies it with an input current I with a first current value h between a first time t1 and a second time t2. The gate G of the respective semiconductor switch 3a, 3b is then briefly partially discharged again.For this purpose, the input current I for the first semiconductor switch 3a briefly assumes a negative value -I2 between the second time t2 and a third time t3. The provision of the negative input current I2 corresponds to the provision of the discharge path. Finally, the gate terminal of the semiconductor switch 3a, 3b to be switched on is charged to the maximum gate charge. For this purpose, an input current I with a third current value I3 is provided to the first semiconductor switch 3a starting at the third time t3. The discharge process temporarily provided during the gate charging has an energy-dissipating effect, i.e., it absorbs the energy of the transient oscillations. Thus, by modifying the gate charge during the switch-on process, the semiconductor switches 3a, 3b achieve a damping effect, eliminating the need for discrete damping components.

Claims

Patent claims 1. Switching device (1) for a power electronics module of a motor vehicle, comprising: - at least one switching unit (2a, 2b) with at least one semiconductor switch (3a, 3b), - a driver circuit (4) connected to a control terminal (G) of the at least one semiconductor switch (3a, 3b), which is designed to provide a charging path for charging the control terminal (G) of the at least one semiconductor switch (3a, 3b) for a switch-on process of the associated switching unit (2a, 2b) and a discharging path for discharging the control terminal (G) of the at least one semiconductor switch (3a, 3b) for a switch-off process of the associated switching unit (2a, 3b), characterized in that the driver circuit (4) for damping switch-on speed-related voltage transients (8a, 8b) of an output voltage (U) of the switching device (1) is designed to temporarily provide the discharging path for at least one semiconductor switch (3a, 3b) of the switching unit (2a, 2b) during a switch-on process of the at least one switching unit (2a, 2b).

2. Switching device (1) according to claim 1, characterized in that the driver circuit (4) is designed to first provide the charging path for a first period of time, then the discharging path for a second period of time and then again the charging path for a third period of time during the switching-on process of the at least one switching unit (2a, 2b) for the at least one semiconductor switch (3a, 3b).

3. Switching device (1) according to claim 2, characterized in that the driver circuit (4) is designed to charge the control terminal to 80% of a maximum charge amount in the first period, to discharge 20% in the second period and to charge it to 100% in the third period.

4. Switching device (1) according to one of the preceding claims, characterized in that the at least one switching unit (2a, 2b) has a plurality of semiconductor switches (3a, 3b) connected in parallel and the driver circuit (4) is designed to provide the discharge path only for some of the semiconductor switches (3a, 3b) connected in parallel.

5. Switching device (1) according to one of the preceding claims, characterized in that the at least one semiconductor switch (3a, 3b) is a power transistor made of a semiconductor material with a wide band gap, in particular silicon carbide and / or gallium nitride.

6. Switching device (1) according to one of the preceding claims, characterized in that the switching device (1) has a commutation cell with two series-connected switching units (2a, 2b), each with at least one semiconductor switch (3a, 3b), wherein the output voltage (U) of the switching device (1) can be switched between a high-side potential (VH) and a low-side potential (Vi_) by switching the switching units (2a, 2b), wherein the driver circuit (4) connected to the control terminals (G) of the semiconductor switches (3a, 3b) is designed to temporarily provide the discharge path for the respective switching unit (2a, 2b) to be switched on during a switching process.

7. Power electronics module for a motor vehicle with at least one switching device (1) according to one of the preceding claims.

8. Power electronics module according to claim 7, characterized in that the power electronics module is an inverter and / or a charger.

9. Motor vehicle with a power electronics module according to claim 7 or 8.

10. Method for switching on a switching unit (2a, 2b) of a switching device (1) according to one of claims 1 to 6, comprising at least one semiconductor switch (3a, 3b), comprising the steps: - charging the control terminal (G) of the at least one semiconductor switch (3a, 3b) to a value below a maximum charge quantity, - discharging the control terminal (G) of the at least one semiconductor switch (3a, 3b) to a predetermined value of the charge quantity; - Charging the control terminal (G) of the at least one semiconductor switch (3a, 3b) to the value of the maximum charge quantity.

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