Inverter circuit and method for operating an electric motor

Abstract

Inverter circuit (100), in particular a three-stage inverter circuit for operating an electric motor of a drive train of an electrically operated vehicle, comprising at least - 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 central terminal (14) for an electrical central potential (S), wherein the central terminal (14) is electrically connected via a capacitor (36) to a center voltage of a vehicle battery of the vehicle, - an output terminal (16) for outputting an alternating voltage (AC) output, - 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 to the output terminal (16), - a bypass path (30) with two bypass switches (32, 34) arranged in a T-shape to the main switches (22, 24), wherein the bypass path (30) is electrically connected on one side to the center terminal (14) and on the other side to the output terminal (16), wherein an inductor (38) is electrically coupled on one side to the center terminal (14) and on the other side via an additional switch (40, 42) to the first input terminal (10) and the second input terminal (12).

Description

[0001] The invention relates to an inverter circuit, in particular a three-stage inverter circuit for operating an electric motor of a drive train of an electrically operated vehicle, and to a method for operating an electric motor, in particular an electric drive train of an electrically operated vehicle, by means of an inverter circuit.

[0002] Two-stage inverters are typically used in battery-electric vehicles. Three-stage inverters are also known and offer significant efficiency potential in electric drive systems. To further 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 by adding 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 power grid. 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 includes 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 output filter inductances of the inverter to be reduced in magnitude.

[0004] CN105680712 B describes a control circuit for a double-T three-stage parallel inverter system. The system comprises two T-shaped three-stage inverters, with the DC sides of the inverters electrically connected in parallel. Each switching element of the inverters is controlled by the control circuit. The AC sides of the inverters are filtered by a filter component and are also electrically connected in parallel to provide grid connection.

[0005] From the scientific publication M. Saleh Khan et al.: Bidirectional Non-Isolated Buck-Boost Three-Phase Unfolding Based Electric Vehicle Powertrain Using Voltage Balancer; 2022 IEEE International Conference on Power Electronics, Drives and Energy Systems (PEDES); Year: 2022; Conference Paper; Publisher: IEEE, a T-type inverter is known, wherein a center terminal of the inverter is coupled to a first input terminal via a capacitor and to a second input terminal of the inverter via another capacitor, and wherein the center terminal is coupled to the two input terminals by means of an inductor and a respective switch.

[0006] From US 2019 / 0 238 062 A1, another T-type inverter with a center connection is known, which is coupled to the input connections of the inverter via a capacitor.

[0007] A three-stage indirect matrix converter and a control procedure are known from CN 1 07 204 714 A.

[0008] From DE 10 2014 226 159 A1 a method for operating an inverter is known which has a basic circuit and a supplementary circuit, wherein in the method requirement data regarding a load of the inverter are determined and the supplementary circuit is operated depending on the requirement data.

[0009] One object of the invention is to create an inverter circuit, in particular a three-stage inverter circuit, for the efficient operation of an electric motor of a drive train of an electrically operated vehicle.

[0010] Another task is to specify a method for the efficient operation of an electric motor, in particular an electric drive train of an electrically operated vehicle, using an inverter circuit.

[0011] The aforementioned tasks are solved using the characteristics of independent claims.

[0012] Favorable embodiments and advantages of the invention will become apparent from the further claims, the description and the drawing.

[0013] According to one aspect of the invention, an inverter circuit, in particular a three-stage inverter circuit for operating an electric motor of a drive train of an electrically operated vehicle, is proposed, comprising at least a first input terminal for a positive DC input voltage and a second input terminal for a negative DC input voltage, a center terminal for an electrical center potential, wherein the center terminal is electrically connected via a capacitor to a center voltage of a vehicle battery of the vehicle, an output terminal for outputting an AC output voltage, a main current path with two main switches, each of which is connected to the first input terminal or the second input terminal.The second input terminal and the other terminal are electrically connected to the output terminal, and a bypass path with two auxiliary switches arranged in a T-shape relative to the main switches, the bypass path being electrically connected on one side to the center terminal and on the other side to the output terminal. An inductor is electrically coupled on one side to the center terminal and on the other side, via an additional switch each, to the first input terminal and the second input terminal.

[0014] The electrical mid-potential represents a voltage level that can lie between the positive and negative input DC voltages. For example, the mid-potential can correspond to half the total input DC voltage, which is the sum of the magnitudes of the positive and negative input DC voltages.

[0015] 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 and voltage waveform that is as sinusoidal as possible for electric motors and to increase the efficiency of the electric powertrain of an electric vehicle.

[0016] Preferably, the first input terminal is provided and / or configured for electrical connection with a positive supply voltage supplied by a vehicle battery of the electrically operated vehicle, and the second input terminal is provided for electrical connection with a negative supply voltage supplied by the vehicle battery.

[0017] The center terminal is not necessarily intended or configured as an input terminal for an electrical voltage (external to the inverter circuit). In particular, the input terminal may be an internal terminal of the inverter circuit.

[0018] In one embodiment, a capacitor of the inverter circuit is integrated via the center terminal into the branch lying at the center potential, the so-called T-branch of the bypass path.

[0019] According to the invention, the center terminal of the inverter circuit is electrically connected to the center voltage of the vehicle battery via the capacitor. For example, the capacitor is electrically connected to the aforementioned voltage on one side and to the center terminal on the other.

[0020] In an alternative or additional embodiment, two capacitors can also be connected in series between the positive and negative input DC voltages, with the common terminal of the two series-connected capacitors being electrically coupled to the center terminal. In this way, the voltage at the center terminal can be adjusted.

[0021] Either one or the common terminal of the two capacitors can be coupled to the positive and negative input DC voltages via an inductor, which in turn can be connected to the positive and negative input DC voltages by means of two transistors acting as switches. This special circuit arrangement makes it possible to set any desired voltage across the capacitor and thus achieve the desired sinusoidal current waveform.

[0022] This can advantageously increase the efficiency of the vehicle's electric powertrain.

[0023] According to an advantageous embodiment of the inverter circuit, the voltage on the bypass path can be variably adjusted using the inductor and the two additional switches. This variable voltage on the bypass path allows for the adjustment of a sinusoidal output current at the output terminal. In this way, an approximately sinusoidal current can be provided at the output terminal for the AC voltage and flow through a connected motor winding. This effectively reduces electrical losses caused by harmonics in the current waveform and by the charging and discharging of the winding capacitances of the electric motor, thereby increasing the efficiency of the drive train.

[0024] According to an advantageous embodiment of the inverter circuit, two diodes connected in series can be reverse-biased and electrically connected to the first and second input terminals, respectively, with the center terminal being electrically coupled to the common terminal of the series-connected diodes. This protective circuit advantageously prevents the voltage at the center terminal from rising above the positive DC input voltage or falling below the negative DC input voltage. This protects the semiconductor switches of the bypass path as well as the additional switches on the inductor.

[0025] According to an advantageous embodiment of the inverter circuit, the main current path can be non-conductive during operation of the secondary current path. This allows the inverter circuit to enable particularly efficient operation of the electric motor at low currents, as the system losses of the electric drive train are reduced.

[0026] According to an advantageous embodiment, the inverter circuit can be switched from three-stage to two-stage operation and vice versa, depending on at least one electrical load requested at the output terminal. The three-stage operation can advantageously enable particularly efficient operation of the inverter circuit in a low load range of the electric motor, while the two-stage operation is typically preferred in a high load range.

[0027] According to a further aspect of the invention, a method for operating an electric motor, in particular an electric drive train of an electrically powered vehicle, is proposed by means of an inverter circuit, comprising at least applying an electrically positive DC input voltage to a first input terminal and an electrically negative DC input voltage to a second input terminal of the inverter circuit; and coupling the electric motor to the at least one output terminal of the inverter circuit. An inductor electrically coupled to a center terminal is controlled via additional switches, which are electrically coupled to the first and second input terminals, the center terminal being electrically connected via a capacitor to a midpoint voltage of a vehicle battery.

[0028] The electrical mean potential represents a voltage level which can lie between the positive input DC voltage and the negative input DC voltage, but preferably corresponds to half of the total input DC voltage from the sum of the magnitudes of the positive and negative input DC voltages.

[0029] The proposed method uses a modification of a prior art three-stage inverter with a so-called T-architecture. Such an inverter circuit makes it possible to provide a current or voltage waveform that is as sinusoidal as possible for electric motors and to increase the efficiency of the electric powertrain of an electric vehicle.

[0030] For example, a capacitor can be integrated via the center terminal into the branch at the center potential, the so-called T-branch of the bypass path. The center potential can be an electrical ground potential.

[0031] In an alternative or additional embodiment, two capacitors can also be connected in series between the positive and negative input DC voltages, with the common terminal of the two series-connected capacitors being electrically coupled to the center terminal. In this way, the voltage at the center terminal can be adjusted.

[0032] Either one or the common terminal of the two capacitors can be coupled to the positive and negative input DC voltages via an inductor, which in turn can be connected to the positive and negative input DC voltages by means of two transistors acting as switches. This special circuit arrangement makes it possible to set any desired voltage across the capacitor and thus achieve the desired sinusoidal current waveform.

[0033] According to an advantageous embodiment of the method, the voltage on the bypass path of the inverter circuit can be variably adjusted using the inductor and the two additional switches. This variable voltage on the bypass path allows for the adjustment of a sinusoidal output current at the output terminal. In this way, an approximately sinusoidal current can be provided at the output terminal for the AC voltage and flow through a connected motor winding. This advantageously reduces electrical losses caused by harmonics of the current waveform and by the charging and discharging of the winding capacitances of the electric motor, thereby increasing the efficiency of the drive train.

[0034] According to an advantageous embodiment of the method, a voltage at the center terminal can be set to be less than or equal to the positive input DC voltage and / or greater than or equal to the negative input DC voltage by means of two diodes connected in series, which are electrically connected in reverse bias to the first and second input terminals, respectively, with the center terminal being electrically coupled to the common terminal of the series-connected diodes. This advantageously prevents the voltage at the center terminal from rising above the positive input DC voltage or falling below the negative input DC voltage. This protects the semiconductor switches of the bypass path as well as the additional switches on the inductor.

[0035] According to an advantageous embodiment of the method, the main current path can be switched to non-conductive operation during the operation of the secondary current path. This allows the inverter circuit to enable particularly efficient operation of the electric motor at low currents, as the system losses of the electric drive train are reduced.

[0036] According to an advantageous embodiment of the method, the inverter circuit can be switched from three-stage to two-stage operation and vice versa, depending on at least one electrical load requested at the output terminal. Three-stage operation enables particularly efficient operation of the inverter circuit in a low load range of the electric motor, while two-stage operation is preferably used in a high load range.

[0037] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0038] This shows: Fig. 1 an inverter circuit, in particular a three-stage inverter circuit for operating an electric motor of a drive train of an electrically operated vehicle, according to an embodiment of the invention; Fig. 2 an inverter circuit according to a further embodiment of the invention with an alternative connection of the center terminal with two capacitors; and Fig. 3 an inverter circuit according to a further embodiment of the invention with a protective circuit as overvoltage protection of the switches in the bypass path.

[0039] The figure merely shows an example and is not to be understood as limiting.

[0040] Fig. Figure 1 shows an inverter circuit 100, in particular a three-stage inverter circuit for operating an electric motor of a drive train of an electrically powered vehicle, according to an embodiment of the invention. The inverter circuit 100 can represent one phase of an inverter for operating a multi-phase electric motor.

[0041] The in Fig. The inverter circuit 100 shown 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 center terminal 14 for an electrical center potential S, and an output terminal 16 for outputting an AC output voltage to one phase of an electric motor (not shown).

[0042] The electrical mean potential S represents a voltage level that can lie between the positive input DC voltage HV+ and the negative input DC voltage HV-, but preferably corresponds to half of the total input DC voltage from the sum of the magnitudes of the positive and negative input DC voltages HV+ and HV-. The mean potential S represents an internal potential of the inverter circuit 100.

[0043] In the Fig. In the embodiment shown in Figure 1, the central terminal 14 is electrically coupled to an electrical ground potential M via a capacitor 36.

[0044] Since an electric motor used in the drivetrain of an electrically powered vehicle is typically a three-phase motor, three phases of the inverter circuit 100 are required to control the electric motor. The entire inverter therefore has three or more, for example six, such inverter circuits 100, as shown in Fig. 1 Inverter circuit 100 shown. The electric motor can, in the case of a three-phase machine, be coupled to the output terminals 16 of at least three such inverter circuits 100.

[0045] The inverter circuit 100 comprises a main current path 20 with two main switches 22, 24, each of which is electrically connected at one terminal to the first input terminal 10 or the second input terminal 12, respectively, and at the other terminal to the output terminal 16. The inverter circuit 100 further comprises a secondary current path 30 with two secondary switches 32, 34 arranged in a T-shape relative to the main switches 22, 24. The secondary current path 30 is electrically connected at one end to the center terminal 14 and at the other end to the output terminal 16. The center terminal 14 is connected in the Fig. In the embodiment shown in Figure 1, the electrical connection is made to the electrical ground potential M via a capacitor 36. An inductor 38 in the form of a coil is electrically coupled on one side to the center terminal 14 and on the other side, via additional switches 40 and 42, to one input terminal 10 and the other input terminal 12.

[0046] In a typical three-stage inverter, for example, the main switches 22, 24 of the main current path 20 can be designed for a current carrying capacity of 800 A rms each (rms = root mean square), while the secondary switches 32, 34 of the secondary current path 30 are designed for a current carrying capacity of 120 A rms each.

[0047] The three-stage inverter circuit 100 can be switched from three-stage to two-stage operation and vice versa, depending on at least one electrical load requested at the output terminal 16. Three-stage operation increases the efficiency of the electric motor in the low-load range.

[0048] The inverter circuit 100 represents an extension of a conventional three-stage inverter with an asymmetrical design of the current carrying capacity of the switching transistors 22, 24, 32, 34.

[0049] Increasing the number of switchable voltage levels can reduce the electrical losses caused by harmonics of the output current. Ideally, a purely sinusoidal current can be generated through the motor winding.

[0050] For this purpose, the proposed three-stage inverter circuit 100 is extended with the components capacitor 36, inductor 38 and the two switching transistors 40, 42. The inductor 38, which is electrically coupled between the capacitor 36 and the bypass switches 32, 34 of the bypass path 30 of the inverter circuit 100, is controlled via the additional switches 40, 42, which are electrically coupled to one input terminal 10 and the other input terminal 12.

[0051] These four components, capacitor 36, inductor 38, and the two switching transistors 40 and 42, allow any desired voltage to be set across capacitor 36. When both transistors 32 and 34 are conducting and a motor winding of an electric motor is connected to output terminal 16, a current flows through the motor winding. Varying the voltage across capacitor 36 results in a corresponding current flowing through the motor winding. The current is approximately sinusoidal. While this part of the circuit is active, the main current path 20 is switched off.

[0052] The circuit for adjusting the voltage via capacitor 36 is only active for low currents. For high motor currents, switches 32 and 34 of the auxiliary current path 30 are non-conducting, and switches 22 and 24 of the main current path 20 are active. The inverter circuit 100 is then operated in conventional two-stage mode.

[0053] By means of the inductor 38 and the two additional switches 40, 42, the voltage across the capacitor 36 of the inverter circuit 100 can be variably adjusted. Using this variable voltage, a sinusoidal output current can be set at the output terminal 16 via the capacitor 36. The main current path 20 can be switched to non-conductive mode during the operation of the secondary current path 30.

[0054] This can advantageously increase the efficiency of the electric motor in the vehicle's electric powertrain.

[0055] In Fig. Figure 2 shows an inverter circuit 100 according to a further embodiment of the invention with an alternative connection of the central terminal 14 with two capacitors 44, 46.

[0056] In this embodiment, the center terminal 14 is electrically coupled to the first input terminal 10 via capacitor 44 and to the second input terminal 12 via the further capacitor 46. Thus, the two capacitors 44 and 46 can be connected between the positive DC input voltage HV+ and the negative DC input voltage HV, with the common terminal of the series-connected capacitors 44 and 46 being electrically coupled to the center terminal 14. In this way, the voltage at the center terminal 14 can be adjusted.

[0057] Similar to the one in Fig. The embodiment shown in 1 can be used in the following example: Fig. In the embodiment shown in Figure 2, the voltage across the capacitors 44 and 46 of the inverter circuit 100 can be variably set using the inductor 38 and the two additional switches 40 and 42. A sinusoidal output current at the output terminal 16 can be set via the variable voltage and the capacitors 44 and 46.

[0058] This can advantageously increase the efficiency of the electric motor in the vehicle's electric powertrain.

[0059] Fig. Figure 3 shows an inverter circuit 100 according to a further embodiment of the invention with a protective circuit as overvoltage protection of the switches 32, 34 in the bypass path 30.

[0060] Here, two series-connected diodes 44, 46 are electrically connected in reverse bias to the first input terminal 10 and the second input terminal 12, with the center terminal 14 being electrically coupled to a common terminal 15 of the series-connected diodes 44, 46.

[0061] The protective circuitry advantageously prevents the voltage at the center terminal 14 from rising above the positive input DC voltage HV+ or falling below the negative input DC voltage HV-. This protects the semiconductor switches 32, 34 of the bypass path 30 as well as the additional switches 40, 42 on the inductor 38.

[0062] Since the remaining circuitry of the in Fig. 3 illustrated embodiment, the one in Fig. In accordance with the embodiment shown in Figure 2, the operating principle for generating the sinusoidal output current at output terminal 16 is the same as in Figure 2. Fig. 2. Reference symbol list 10 first input connection 12 second input connection 14 Center connection 15 common connection 16 Output port 20 Main flow path 22 Main switches 24 main switches 30 Sidestream path 32 auxiliary switches 34 auxiliary switches 36 Capacitor 38 Inductance / coil 40 switches 42 switches 44 Capacitor 46 Capacitor 48 diodes 50 diode 100 Inverter circuit DC+ positive input DC voltage DC negative input DC voltage AC output voltage M electrical mass S Medium potential

Claims

[1] Inverter circuit (100), in particular a three-stage inverter circuit for operating an electric motor of a drive train of an electrically powered vehicle, comprising at least - 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 central terminal (14) for an electrical central potential (S), wherein the central terminal (14) is electrically connected via a capacitor (36) to a center voltage of a vehicle battery of the vehicle, - an output terminal (16) for outputting an alternating voltage (AC) output, - 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 to the output terminal (16), - a bypass path (30) with two bypass switches (32, 34) arranged in a T-shape to the main switches (22, 24), wherein the bypass path (30) is electrically connected on one side to the center terminal (14) and on the other side to the output terminal (16), wherein an inductor (38) is electrically coupled on one side to the center terminal (14) and on the other side via an additional switch (40, 42) to the first input terminal (10) and the second input terminal (12). [2] Inverter circuit according to claim 1, wherein a voltage on the bypass path (30) can be variably adjusted by means of the inductor (38) and the two additional switches (40, 42), wherein a sinusoidal output current at the output terminal (16) can be adjusted by means of the variable voltage on the bypass path (30). [3] Inverter circuit according to one of the preceding claims, wherein two series-connected diodes (44, 46) are electrically connected in reverse bias to the first input terminal (10) and the second input terminal (12), wherein the center terminal (14) is electrically coupled to the common terminal (15) of the series-connected diodes (44, 46). [4] Inverter circuit according to one of the preceding claims, wherein the main current path (20) is switched to non-conductive operation during the operation of the secondary current path (30). [5] Inverter circuit according to one of the preceding claims, wherein the inverter circuit (100) can be converted from a three-stage operation to a two-stage operation and vice versa depending on at least one electrical load requested at the output terminal (16). [6] Method for operating an electric motor, in particular an electric drive train of an electrically powered vehicle, by means of an inverter circuit (100) according to one of the preceding claims, at least comprising Applying an electrically positive DC input voltage (DC+) to a first input terminal (10) and an electrically negative DC input voltage (DC-) to a second input terminal (12) of the inverter circuit (100); Coupling the electric motor with at least one output terminal (16) of the inverter circuit (100), wherein an inductor (38) electrically coupled to a central terminal (14) of the inverter circuit (100) is controlled via additional switches (40, 42) which are electrically coupled to the first input terminal (10) and the second input terminal (12), wherein the central terminal (14) is electrically connected via a capacitor (36) to a midpoint voltage of a vehicle battery of the vehicle. [7] Method according to claim 6, wherein a voltage on the bypass path (30) of the inverter circuit (100) is variably set by means of the inductor (38) and the two additional switches (40, 42), wherein a sinusoidal output current is set at the output terminal (16) by means of the variable voltage on the bypass path (30). [8] Method according to claim 6 or 7, wherein by means of two diodes (44, 46) connected in series, which are electrically connected in reverse bias to the first input terminal (10) and the second input terminal (12), wherein the center terminal (14) is electrically coupled to a common terminal (15) of the diodes (44, 46) connected in series, a voltage at the center terminal (14) less than or equal to the positive DC input voltage (HV+) and / or greater than or equal to the negative DC input voltage (HV-) is set. [9] Method according to any one of claims 6 to 8, wherein the main current path (20) is switched to non-conductive operation during the operation of the secondary current path (30). [10] Method according to one of claims 6 to 9, wherein the inverter circuit (100) is switched from a three-stage operation to a two-stage operation and vice versa depending on at least one electrical load requested at the output terminal (16).

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