Method for operating an inverter, inverter, drive train, motor vehicle, method for operating a motor vehicle

Abstract

Method for operating an inverter (1), in particular an inverter (1) for a motor vehicle, having a plurality of switching units (8), wherein at least one, preferably all, switching units (8) have a first power semiconductor (2) and a second power semiconductor (3) connected in parallel to the first power semiconductor (2), wherein the second power semiconductor (3) is switched as a function of an operating point of the first power semiconductor (2), wherein, for switching the second power semiconductor (3), a control unit (5) sends a signal for opening or closing the second semiconductor (3) to a gate input of the second power semiconductor (3), wherein, for opening, a galvanic connection is established between an input of the second power semiconductor (3) and an output of the second line semiconductor (3) by the second power semiconductor (3), and for closing, the galvanic connection is interrupted.wherein the control unit (5) sends a signal to open the second power semiconductor (3) when the operating point of the first power semiconductor (2) exceeds a limit value, wherein the limit value corresponds to an operating limit of the first power semiconductor (2), wherein the operating limit is an operating point at which a further increase in current flow through and / or voltage applied to the first power semiconductor (2) would lead to an increase in the conduction losses at the first power semiconductor (2).

Description

[0001] The present invention relates to a method for operating an inverter with a plurality of switching units, wherein the switching units have a first power semiconductor and a second power semiconductor connected in parallel to the first power semiconductor.

[0002] In electrically powered vehicles, an inverter converts a direct current into an alternating current, which is used to power the vehicle's electric motor during operation. For this purpose, the inverters used typically have switching units with power semiconductors. A three-phase inverter, for example, has six switching units. To ensure the inverter's current-carrying capacity, several power semiconductors are connected in parallel within the switching units. To open and close the power semiconductors, it is common practice to switch the parallel-connected power semiconductors simultaneously.

[0003] For the effective and efficient operation of an electric vehicle, it is essential to minimize losses. This particularly applies to losses in the inverter. In addition to losses when current passes through the power semiconductors, losses also occur when the power semiconductors are switched.

[0004] From US 2018 / 0 138 904 A1, it is known to switch a second transistor depending on the switching state of a first transistor connected in parallel with the second transistor. DE 10 2015 223 465 A1 discloses a method for temperature-dependent control of a switching element, for example, in an inverter. From DE 10 2014 224 172 A1, it is known to switch several power semiconductors connected in parallel with each other with a time delay to protect the power semiconductors.

[0005] It is therefore an object of the present invention to provide a method for operating an inverter which is less lossy.

[0006] This object is achieved by a method according to claim 1.

[0007] Switching and conduction losses depend on the operating point of the power semiconductors. The method according to the invention makes it possible to take this into account. The first power semiconductor and the second power semiconductor are not simply switched simultaneously. Instead, the switching of the second power semiconductor occurs depending on the situation, namely the operating point of the first power semiconductor. By skillfully switching the parallel power semiconductors of the switching units, the efficiency of the inverter's operation is significantly increased.

[0008] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings.

[0009] According to the invention, it is provided that, in order to switch the second power semiconductor, a control unit sends a signal for opening or closing the second semiconductor to a gate input of the second power semiconductor, wherein a galvanic connection is established between an input of the second power semiconductor and an output of the second line semiconductor by the second power semiconductor for opening and the galvanic connection is interrupted for closing.It is conceivable that, in order to switch the first power semiconductor, a signal for opening or closing the first power semiconductor is sent to a gate input of the first semiconductor from a control unit or from a further control unit, wherein a galvanic connection is established between an input of the first power semiconductor and an output of the first conduction semiconductor by the first power semiconductor for opening and the galvanic connection is interrupted for closing.

[0010] According to the invention, the control unit sends a signal to open the second power semiconductor when the operating point of the first power semiconductor exceeds a limit value. This advantageously makes it possible to switch very efficiently when the switching losses are greater than the conduction losses of the switching unit. The limit value of the operating point corresponds to an operating limit of the first power semiconductor. An operating limit within the meaning of the present invention is an operating point at which a further increase in the current flow through and / or voltage applied to the first power semiconductor would lead to an increase in the conduction losses at the first power semiconductor.

[0011] According to a further preferred embodiment of the invention, it is provided that the control unit sends a signal to close the second power semiconductor when the operating point of the first power semiconductor exceeds a limit value. This advantageously makes it possible to switch very efficiently when the forward losses are greater than the switching losses of the switching unit. In particular, it is conceivable for the limit value of the operating point to correspond to an operating limit of the first power semiconductor. An operating limit within the meaning of the present invention is, in particular, an operating point at which a further increase in current flow through and / or voltage applied to the first power semiconductor would lead to an increase in the forward losses at the first power semiconductor.

[0012] It is also conceivable, however, for the control unit to send a signal to open or close the second power semiconductor when the operating point of the first power semiconductor exceeds a limit, so that the power loss of the switching unit is increased and preferably maximized. This advantageously makes it possible to quickly generate a large amount of heat and, for example, to heat a coolant.

[0013] It is also conceivable that the first power semiconductor and the second power semiconductor are switched alternately to switch the switching unit. This achieves a uniform load on the power semiconductors.

[0014] According to a further preferred embodiment of the invention, the operating point of the first power semiconductor is monitored by the control unit. This ensures that the second power semiconductor is switched on at the correct time.

[0015] According to a further preferred embodiment of the invention, it is provided that a third power semiconductor of the switching unit, which is connected in parallel to the second power semiconductor, is switched depending on an operating point of the second power semiconductor, wherein, preferably, for switching the third power semiconductor, a control unit sends a signal for opening or closing the third power semiconductor to a gate input of the third power semiconductor, wherein, for opening, the third power semiconductor establishes a galvanic connection between an input of the third power semiconductor and an output of the third line semiconductor, and for closing, the galvanic connection is interrupted, wherein, particularly preferably, a signal for opening the third power semiconductor is sent when the operating point of the second power semiconductor exceeds a limit value.This advantageously allows the inverter to operate with even lower losses. It is conceivable that additional power semiconductors connected in parallel with the third power semiconductor could be switched depending on the operating point of other power semiconductors connected in parallel.

[0016] A further object of the invention for solving the problem formulated at the outset is an inverter comprising a plurality of switching units, wherein at least one, preferably all, switching units each comprise a first power semiconductor and a second power semiconductor. The inverter comprises a control unit, wherein the control unit is configured to carry out a method according to the invention for operating the inverter and to switch the second power semiconductor depending on the operating point of the first power semiconductor. The first power semiconductor and the second power semiconductor are connected in parallel.

[0017] According to a further preferred embodiment of the invention, it is provided that the at least one, preferably all, switching units each have a third power semiconductor, wherein the control unit is configured to switch the third power semiconductor depending on an operating point of the second power semiconductor.

[0018] A further object of the invention to solve the problem formulated at the outset is a drive train comprising a battery, an inverter according to the invention and an electric machine.

[0019] A further object of the invention to solve the problem formulated at the outset is a motor vehicle having a drive train according to the invention.

[0020] However, another, preferably industrial, environment is also conceivable, which has the drive train according to the invention.

[0021] A further object of the invention to solve the problem formulated at the outset is a method for operating a motor vehicle according to the invention, wherein the inverter is operated with the method according to the invention.

[0022] All details, features, and advantages previously disclosed in connection with the method according to the invention for operating an inverter also relate to the inverter according to the invention, the drive train according to the invention, the motor vehicle according to the invention, and the method according to the invention for operating a motor vehicle. Further details, features, and advantages of the invention will become apparent from the drawings and from the following description of preferred embodiments with reference to the drawings. The drawings merely illustrate exemplary embodiments of the invention, which do not limit the inventive concept. Fig. 1 schematically illustrates an inverter according to an exemplary embodiment of the present invention, which is operated with a method according to an exemplary embodiment of the present invention. Fig. 2 schematically illustrates a motor vehicle according to an exemplary embodiment of the present invention having a drive train according to an exemplary embodiment of the present invention, which is operated with a method according to an exemplary embodiment of the present invention.

[0023] Fig. 1 schematically illustrates an inverter 1 according to an exemplary embodiment of the present invention, which is operated using a method according to an exemplary embodiment of the present invention. The inverter 1, a three-phase inverter is shown here, has six switching units 8. Each of the switching units 8, in turn, has a first power semiconductor 2, a second power semiconductor 3 connected in parallel to the first power semiconductor 2, and a third power semiconductor 4 connected in parallel to the second power semiconductor 3, which can be seen in the exemplary enlarged detailed view of one of the switching units 8.

[0024] During operation of the inverter 1, the power semiconductors 2, 3, 4 of the switching units 8 are opened and closed, i.e. a galvanic connection is established or broken between the inputs of the power semiconductors 2, 3, 4 and the outputs of the power semiconductors 2, 3, 4 and thus between the inputs of the switching units 8 and the outputs of the switching units 8.

[0025] To control the opening and closing of the power semiconductors 2, 3, 4, the inverter 1 has a control unit 5 or preferably a plurality of control units 5, 6, 7. It is conceivable that each switching unit 8 has one control unit or a plurality of control units 5, 6, 7. Shown here is an inverter 1 whose switching units 8 each have a control unit 5 for controlling the second power semiconductor 3, a further control unit 7 for controlling the first power semiconductor 2, and an additional control unit 6 for controlling the third power semiconductor 4. To open a power semiconductor 2, 3, 4, a voltage is applied by the respective control unit 5, 6, 7 to a control input, for example to a gate input of the corresponding power semiconductor 2, 3, 4.

[0026] To reduce switching losses, the power semiconductors 2, 3, 4 are not opened at the same time. After the first power semiconductor 2 is opened, its operating point is monitored by the control unit 5. For this purpose, the phase current is measured by the switching unit 8 with the power semiconductors 2, 3, 4. If the operating point of the first power semiconductor 2 reaches the operating limit of the first power semiconductor 2, the second power semiconductor 3 is switched and closed by the control unit 5. If the operating point of the second power semiconductor 2, which is monitored by the additional control unit 6, reaches the operating limit of the second power semiconductor 3, the third power semiconductor 4 is switched and closed by the additional control unit 6. The first power semiconductor 2 is switched by the additional control unit 7.

[0027] The described method makes it possible to significantly reduce switching losses in inverter 1.

[0028] Fig. 2 schematically illustrates a motor vehicle 200 according to an exemplary embodiment of the present invention, having a drivetrain 100 according to an exemplary embodiment of the present invention, which is operated using a method according to an exemplary embodiment of the present invention. The drivetrain 100 includes a battery 101, an electric machine 102, and an inverter 1 according to an exemplary embodiment of the present invention. The inverter 1 is operated using a method according to an exemplary embodiment of the present invention.

Claims

[1] Method for operating an inverter (1), in particular an inverter (1) for a motor vehicle, having a plurality of switching units (8), wherein at least one, preferably all, switching units (8) have a first power semiconductor (2) and a second power semiconductor (3) connected in parallel to the first power semiconductor (2), wherein the second power semiconductor (3) is switched as a function of an operating point of the first power semiconductor (2), wherein, for switching the second power semiconductor (3), a control unit (5) sends a signal for opening or closing the second semiconductor (3) to a gate input of the second power semiconductor (3), wherein, for opening, a galvanic connection is established between an input of the second power semiconductor (3) and an output of the second line semiconductor (3) by the second power semiconductor (3), and for closing, the galvanic connection is interrupted,wherein the control unit (5) sends a signal to open the second power semiconductor (3) when the operating point of the first power semiconductor (2) exceeds a limit value, wherein the limit value corresponds to an operating limit of the first power semiconductor (2), wherein the operating limit is an operating point at which a further increase in current flow through and / or voltage applied to the first power semiconductor (2) would lead to an increase in the conduction losses at the first power semiconductor (2). [2] Method according to claim 1, wherein the operating point of the first power semiconductor (2) is monitored by the control unit (5). [3] Method according to one of the preceding claims, wherein a third power semiconductor (4) of the switching unit (8) connected in parallel to the second power semiconductor (3) is switched depending on an operating point of the second power semiconductor (3), wherein, preferably for switching the third power semiconductor (4), a signal for opening or closing the third power semiconductor (4) is sent from the control unit (5) or an additional control unit (6) to a gate input of the third power semiconductor (4), wherein, for opening, the third power semiconductor (4) establishes a galvanic connection between an input of the third power semiconductor (4) and an output of the third line semiconductor (4), and for closing, the galvanic connection is interrupted, wherein, particularly preferably, a signal for opening the third power semiconductor (4) is sent,if the operating point of the second power semiconductor (3) exceeds a limit value., [4] Inverter (1) comprising a plurality of switching units (8), wherein at least one, preferably all, switching units (8) each have a first power semiconductor (2) and a second power semiconductor (3), wherein the inverter (1) has a control unit (6), wherein the control unit (6) is configured to carry out a method for operating the inverter (1) according to one of claims 1 to 3 and to switch the second power semiconductor (3) depending on the operating point of the first power semiconductor (2). [5] Inverter (1) according to claim 4, wherein the inverter (1) comprises a third power semiconductor (4), wherein the control unit (6) is configured to carry out a method according to claim 3. [6] Drive train (100) comprising a battery (101), an inverter (1) according to one of claims 4 to 5, and an electric machine (102). [7] Motor vehicle (200) comprising a drive train (100) according to claim 6. [8] Method for operating a motor vehicle (200) according to claim 7, wherein the inverter (1) is operated using a method according to one of claims 1 to 3.

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