Inverter circuit for operating an electrical machine and inverter with three inverter circuits

Abstract

Inverter circuit (100) for operating an electric machine of a drive train of an electrically operable vehicle, at least comprising - a first input terminal (10) for a positive input DC voltage (DC+) and a second input terminal (12) for a negative input DC voltage (DC-), - a neutral point (14) which is electrically connected to the first input terminal (10) via a capacitor (44) and to the second input terminal (12) via a further capacitor (46), - an output terminal (16) for outputting an alternating voltage (AC), - a main current path (20) with two main switches (22, 24), each of which is electrically connected with one terminal to the first input terminal (10) or the second input terminal (12) and with the other terminal together to the output terminal (16), - a secondary current path (30) with two secondary switches (32, 36) arranged in a T-shape to the main switches (22, 24), which are electrically connected to a common central terminal (15), wherein the secondary current path (30) is electrically connected on the one hand to the neutral point (14) and on the other hand to the output terminal (16), wherein the central terminal (15) is damped by a passive filter (40), characterized in that the passive filter (40) has a first filter branch with a resistor (42) connected in series with a capacitor (44) and a second filter branch with a resistor (48) connected in series with a capacitor (46), the first and second filter branches being connected in series, wherein the first filter branch is electrically coupled between the first input terminal (10) and the center terminal (15) and the second filter branch is electrically coupled between the center terminal (15) and the second input terminal (12).

Description

[0001] The invention relates to an inverter circuit for operating an electric machine of a drive train of an electrically operated vehicle and to an inverter having at least three inverter circuits.

[0002] Two-stage inverters are typically used in battery-electric vehicles. Three-stage inverters are well-known and offer significant efficiency potential in electric drive systems. To increase the efficiency of the electric motor in the cycle-relevant range, a two-stage inverter can be extended to a three-stage ground-point-coupled inverter using a so-called T-branch.

[0003] EP 2 975 756 A1 discloses an inverter for converting direct current (DC) from a power generator into three-phase alternating current (AC) from a three-phase network. The inverter comprises a primary side with a first DC input line and a second DC input line, a secondary side with a first AC output phase, a second AC output phase, and a third AC output phase, and a filter component for connecting the secondary side to the primary side via a return line. The filter component comprises a first capacitive element and a first switching element connected to the return line. The first AC output phase is connected to the first capacitive element and the first switching element. The filter component allows the size of the inverter's output filter inductances to be reduced.

[0004] WO 2020 / 079 019 A1 describes a multiphase converter topology for transmitting electrical energy from an AC input with mains phase connections to a DC output, or vice versa. The multiphase converter topology comprises a power section with half-bridges for switching currents, an AC filter connected between the power section and the AC input, and one or more DC blocks connected between the power section and the DC output. The AC filter has at least one AC filter stage with input terminals, output terminals, and a ground connection.The mains phase connections are connected in parallel to each other and form a first phase connection for the connection of a single-phase alternating voltage, and a neutral conductor connection of the alternating voltage filter forms a neutral conductor connection of the alternating voltage input and a second phase connection for the connection of the single-phase alternating voltage.

[0005] An object of the invention is to provide an improved inverter circuit for operating an electric machine of a drive train of an electrically operable vehicle.

[0006] Another task is to create an improved inverter with at least three inverter circuits.

[0007] The above-mentioned objects are solved by the features of the independent claims.

[0008] Advantageous embodiments and advantages of the invention emerge from the further claims, the description and the drawing.

[0009] According to one aspect of the invention, an inverter circuit for operating an electric machine of a drive train of an electrically operated vehicle is proposed, at least comprising a first input terminal for a positive input DC voltage and a second input terminal for a negative input DC voltage, a neutral point which is electrically connected via a capacitor to the first input terminal and via a further capacitor to the second input terminal, an output terminal for outputting an output AC voltage, a main current path with two main switches, each of which is connected with a terminal to the first input terminal orthe second input terminal and the other terminal are electrically connected to the output terminal; a secondary current path with two secondary switches arranged in a T-shape to the main switches, which are electrically connected to a common center terminal, with the secondary current path being electrically connected to the neutral point on one side and to the output terminal on the other. The center terminal is attenuated with a passive filter.

[0010] The proposed inverter circuit represents an advantageous further development of a known three-stage inverter with a so-called T-architecture. With such an inverter circuit, it is possible to provide a current or voltage curve that is as sinusoidal as possible for electrical machines and to increase the efficiency of the electric drive train of an electrically operated vehicle.

[0011] In an inverter circuit, the auxiliary switches of the auxiliary current path carry less current than the main switches of the main current path. This requires switching to a two-stage operating mode in the high current range, which means that the auxiliary switches are turned off and the main switches operate in push-pull mode. The center potential between the center terminal of the auxiliary current path and the first input terminal or the second input terminal is fixed in its voltage level only by the parasitic capacitances.

[0012] The passive filter, which damps the center connection, prevents the node of the center connection from oscillating strongly. Any oscillation that would otherwise occur is advantageously dampened by the passive filter.

[0013] In this way, the susceptibility to faulty switching of the gate driver circuits of the auxiliary switches can be reduced.

[0014] Furthermore, the passive filter can advantageously improve the behavior of the inverter circuit with regard to electromagnetic compatibility (EMC).

[0015] According to the invention, the passive filter comprises a first filter branch with a resistor connected in series with a capacitor, and a second filter branch with a resistor connected in series with a capacitor, wherein the first and second filter branches are connected in series. Such a filter circuit advantageously has a center tap between the two filter branches, which can be connected to the center terminal of the secondary current path. This allows the filtering effect to be achieved in a favorable manner.

[0016] According to the invention, the first filter branch is electrically coupled between the first input terminal and the center terminal, and the second filter branch is electrically coupled between the center terminal and the second input terminal. This advantageously allows oscillations of the center potential to be damped.

[0017] According to an advantageous embodiment of the inverter circuit, the first filter branch can be electrically coupled between the neutral point and the center terminal, and the second filter branch can be electrically coupled between the center terminal and the output terminal. This alternative arrangement of the passive filter can also advantageously dampen oscillations of the center potential.

[0018] According to an advantageous embodiment of the inverter circuit, the two auxiliary switches can each be electrically connected to the center terminal via their source electrodes. The damping effect of the passive filter can have a beneficial effect with this arrangement of the two auxiliary switches.

[0019] According to an advantageous embodiment of the inverter circuit, the two secondary switches can each be electrically connected to the center terminal via their drain electrodes. Even with this alternative arrangement of the two secondary switches, the damping effect of the passive filter can have a beneficial effect.

[0020] According to an advantageous embodiment, the inverter circuit can be configured in three stages. Such an inverter circuit makes it possible to provide a current or voltage curve that is as sinusoidal as possible for electrical machines and to increase the efficiency of the electric drive train of an electrically powered vehicle. Advantageously, three-stage operation with higher inverter efficiency can be implemented at low current requirements, and two-stage operation with lower efficiency at higher current requirements.

[0021] According to an advantageous embodiment, the inverter circuit can be switchable between three-stage operation and two-stage operation depending on at least one electrical load requested at the output terminal. Three-stage operation can advantageously enable particularly efficient operation of the inverter circuit in a low load range of the electrical machine, while two-stage operation is usually preferred in a high load range.

[0022] According to an advantageous embodiment of the inverter circuit, a capacitor can be connected between the first input terminal and the second input terminal.

[0023] The first input terminal can be electrically connected to a first input potential via a resistor connected in series with a capacitor, and the second input terminal can be electrically connected to a second input potential via another resistor connected in series with another capacitor. In this way, the potential voltage at the neutral point can be adjusted to a favorable value. This special circuit arrangement makes it possible to set any voltage across the input network, thus achieving the desired sinusoidal current waveform of the inverter circuit.

[0024] According to a further aspect of the invention, an inverter with at least three inverter circuits described above is proposed, which is electrically configured to operate a three-phase electrical machine. The inverter is switchable between three-stage operation and two-stage operation depending on at least one electrical load required at the output terminals.

[0025] In the proposed inverter, the inverter circuits can be used to provide a current or voltage curve that is as sinusoidal as possible for the at least three phases of the electric machine and to favorably increase the efficiency of the electric drive train of an electrically operated vehicle.

[0026] In three-stage inverter circuits, the auxiliary switches of the auxiliary current path carry less current than the main switches of the main current path. This requires switching to a two-stage operating mode in the high current range, which means that the auxiliary switches are turned off and the main switches operate in push-pull mode. The center potential between the center terminal of the auxiliary current path and the first input terminal or the second input terminal is fixed in its voltage level only by the parasitic capacitances.

[0027] The passive filter in the inverter circuits, which damps the center terminal, prevents the node at the center terminal from oscillating excessively. Any oscillation that would otherwise occur is advantageously dampened by the passive filter.

[0028] In this way, the susceptibility to faulty switching of the gate driver circuits of the auxiliary switches can be reduced.

[0029] Furthermore, the passive filter can advantageously improve the behavior of the inverter circuit with regard to electromagnetic compatibility (EMC).

[0030] Advantageously, the inverter can be switchable between three-stage operation and two-stage operation. Advantageously, three-stage operation with higher inverter efficiency can be used for low power requirements, and two-stage operation with lower efficiency for higher power requirements.

[0031] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an exemplary embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also expediently consider the features individually and combine them into useful further combinations.

[0032] Showing: Fig. 1 shows an inverter circuit for operating an electric machine of a drive train of an electrically operable vehicle according to an embodiment of the invention; and Fig. 2 an inverter circuit according to a further embodiment of the invention.

[0033] In the figures, identical or similar components are numbered with the same reference numerals. The figures show only examples and are not to be understood as limiting.

[0034] Fig. Figure 1 shows an inverter circuit 100 for operating an electric machine of a drive train of an electrically operable vehicle according to an exemplary embodiment of the invention. Inverter circuit 100 can represent one phase of an inverter for operating a multiphase electric machine.

[0035] The Fig. The inverter circuit 100 shown in Figure 1 comprises a first input terminal 10 for a positive DC input voltage DC+ and a second input terminal 12 for a negative DC input voltage DC-, a neutral point 14 which is electrically connected to the first input terminal 10 via a capacitor 44 and to the second input terminal 12 via a further capacitor 46, and an output terminal 16 for outputting an AC output voltage AC.

[0036] The inverter circuit 100, which is designed in three stages, comprises a main current path 20 with two main switches 22, 24, each of which is electrically connected by one terminal to the first input terminal 10 and the second input terminal 12, respectively, and by the other terminal jointly to the output terminal 16, as well as a secondary current path 30 with two secondary switches 32, 36 arranged in a T-shape to the main switches 22, 24, which are electrically connected to a common center terminal 15. The secondary current path 30 is electrically connected on the one hand to the neutral point 14 and on the other hand to the output terminal 16.

[0037] The inverter circuit 100 can thus be switched between a three-stage operation and a two-stage operation depending on at least one electrical load requested at the output terminal 16.

[0038] A capacitor 54 is connected between the first input terminal 10 and the second input terminal 12. The first input terminal 10 is electrically connected to a first input potential 70 via a resistor 60 connected in series with a capacitor 62. The second input terminal 12 is electrically connected to a second input potential 72 via a further resistor 66 connected in series with another capacitor 64.

[0039] The two secondary switches 32, 36 each consist of at least one semiconductor switch, for example a so-called insulated-gate bipolar transistor (IGBT) or a so-called metal oxide semiconductor field-effect transistor (MOSFET), through which a current flows that depends on the semiconductor switch properties, such as material and / or size.

[0040] The auxiliary switches 32, 36 of the Fig. 1 are each electrically connected to the center terminal 15 by their source electrodes 33, 37.

[0041] In an alternative embodiment, not shown, the two secondary switches 32, 36 can also each be electrically connected to the center terminal 15 via their drain electrodes 34, 38.

[0042] The center connection 15 of the secondary current path 30 is attenuated with a passive filter 40.

[0043] The inverter circuit 100 represents a three-stage inverter with a so-called T-architecture. With such an inverter circuit, it is possible to provide a current or voltage curve that is as sinusoidal as possible for electrical machines and to increase the efficiency of the electric drive train of an electrically operated vehicle.

[0044] In inverter circuit 100, the auxiliary switches 32, 36 of the auxiliary current path 30 carry less current than the main switches 22, 24 of the main current path 20. As a result, a two-stage operating mode must be switched to in the high current range, which means that the auxiliary switches 32, 36 are switched off and the main switches 22, 24 are operated in push-pull mode. The center potential present between the center terminal 15 of the auxiliary current path 30 and the first input terminal 10 or the second input terminal 12 is fixed in its voltage level only by the parasitic capacitances.

[0045] The passive filter 40, which damps the center connection 15, prevents the node of the center connection 15 from oscillating strongly. Any oscillation that would otherwise occur is advantageously dampened by the passive filter 40.

[0046] Furthermore, the passive filter can advantageously improve the behavior of the inverter circuit 100 with regard to electromagnetic compatibility.

[0047] The passive filter 40 has a first filter branch with a resistor 42 connected in series with a capacitor 44 and a second filter branch with a resistor 48 connected in series with a capacitor 46. The first and second filter branches are connected in series.

[0048] In the Fig. 1, the first filter branch is electrically coupled between the first input terminal 10 and the center terminal 15 and the second filter branch is electrically coupled between the center terminal 15 and the second input terminal 12.

[0049] In Fig. 2 shows an inverter circuit 100 according to a further embodiment of the invention.

[0050] In this embodiment, which is essentially the same as in Fig. 1, the first filter branch is electrically coupled between the neutral point 14 and the center terminal 15 and the second filter branch is electrically coupled between the center terminal 15 and the output terminal 16.

[0051] In this way, the center connection 15 can also be damped with the passive filter 40 to prevent the node of the center connection 15 from oscillating strongly. Oscillation that would otherwise occur can be advantageously damped by the passive filter 40.

[0052] The behavior of the inverter circuit 100 with regard to electromagnetic compatibility can also be advantageously improved.

[0053] Advantageously, an inverter (not shown) can be implemented with at least three of the illustrated inverter circuits 100, which is electrically configured to operate a three-phase electrical machine. The inverter can be switched between three-stage operation and two-stage operation depending on at least one electrical load requested at the output terminals 16.

[0054] The inverter has a favorable operating behavior with a greatly reduced tendency to oscillations of a center potential of the center terminal 15 of the secondary current path 30 of the inverter circuits 100. List of reference symbols 10 Input connection 12 Input connection 14 Neutral point 15 Central connection 16 Output connector 20 Main current path 22 Main switch 24 main switches 30 bypass path 32 auxiliary switches 33 Source electrode 34 Drain electrode 35 Gate electrode 36 auxiliary switches 37 Source electrode 38 Drain electrode 39 Gate electrode 40 filters 42 Resistance 44 Capacitor 46 Capacitor 48 Resistance 50 capacitor 52 Capacitor 54 Capacitor 60 resistance 62 Capacitor 64 capacitor 66 Resistance 70 first input potential 72 second input potential 100 inverter circuit AC output voltage DC- negative input DC voltage DC+ positive input DC voltage

Claims

[1] Inverter circuit (100) for operating an electric machine of a drive train of an electrically operable vehicle, at least comprising - a first input terminal (10) for a positive input DC voltage (DC+) and a second input terminal (12) for a negative input DC voltage (DC-), - a neutral point (14) which is electrically connected to the first input terminal (10) via a capacitor (44) and to the second input terminal (12) via a further capacitor (46), - an output terminal (16) for outputting an alternating voltage (AC), - a main current path (20) with two main switches (22, 24), each of which is electrically connected with one terminal to the first input terminal (10) or the second input terminal (12) and with the other terminal together to the output terminal (16), - a secondary current path (30) with two secondary switches (32, 36) arranged in a T-shape to the main switches (22, 24), which are electrically connected to a common central terminal (15), wherein the secondary current path (30) is electrically connected on the one hand to the neutral point (14) and on the other hand to the output terminal (16), wherein the central terminal (15) is damped by a passive filter (40), characterized by in that the passive filter (40) has a first filter branch with a resistor (42) connected in series with a capacitor (44) and a second filter branch with a resistor (48) connected in series with a capacitor (46), wherein the first and the second filter branch are connected in series, wherein the first filter branch is electrically coupled between the first input terminal (10) and the center terminal (15) and the second filter branch is electrically coupled between the center terminal (15) and the second input terminal (12). [2] Inverter circuit according to claim 1, wherein the first filter branch is electrically coupled between the neutral point (14) and the center terminal (15) and the second filter branch is electrically coupled between the center terminal (15) and the output terminal (16). [3] Inverter circuit according to one of claims 1 or 2, wherein the two sub-switches (32, 36) are each electrically connected by their source electrode (33, 37) to the central terminal (15). [4] Inverter circuit according to one of claims 1 or 2, wherein the two sub-switches (32, 36) are each electrically connected by their drain electrode (34, 38) to the center terminal (15). [5] Inverter circuit according to one of the preceding claims, which is designed in three stages. [6] Inverter circuit according to one of the preceding claims, which is switchable between a three-stage operation and a two-stage operation depending on at least one electrical load requested at the output terminal (16). [7] Inverter circuit according to one of the preceding claims, wherein a capacitor (54) is connected between the first input terminal (10) and the second input terminal (12), wherein the first input terminal (10) is electrically connected to a first input potential (70) via a resistor (60) connected in series with a capacitor (62), and wherein the second input terminal (12) is electrically connected to a second input potential (72) via a further resistor (66) connected in series with a further capacitor (64). [8] Inverter with at least three inverter circuits (100) according to one of the preceding claims, which is electrically designed to operate a three-phase electrical machine, wherein the inverter is switchable between a three-stage operation and a two-stage operation depending on at least one electrical load requested at the output terminals (16).

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