DE102023005020A1 - Double inverter and method for operating a double inverter - Google Patents

Abstract

The invention relates to a double inverter (1) comprising two inverter modules (2.1, 2.2), each comprising three half-bridges made of semiconductor switches (S1 to S19), each having three phase connections, between which an inductive load (3), in particular an electrical machine (3) is switchable or connected, which has three stator windings (L1, L2, L3), wherein a switchable connection (4) is provided between high-voltage potentials (HV+, HV-) of the two inverter modules (2.1, 2.2), which are connectable or connected to a battery (5), wherein a separating element (S13) designed as a semiconductor switch (S13) is arranged between the battery (5) and one of the inverter modules (2.1, 2.2) and/or between the two inverter modules (2.1, 2.2) in one of the two high-voltage potentials (HV+, HV-) of the connection (4), characterized in that at least one of the semiconductor switches (S1 to S19) is designed as a parallel circuit comprising an IGBT and a MOSFET.

Description

The invention relates to a double inverter according to the preamble of claim 1 and a method for operating a double inverter according to the preamble of claim 9.

DE 10 2022 132 370 A1 describes a device that enables a two-level inverter to switch between modes. The device comprises a first inverter unit, a second inverter unit, a load connected between the first inverter unit and the second inverter unit, a mode switching unit connected between the load and the second inverter unit, and a control unit configured to drive the load in a single-level inverter mode or a two-level inverter mode by performing control to turn the mode switching unit on or off.

The invention is based on the object of providing a novel double inverter and a novel method for operating a double inverter.

The object is achieved according to the invention by a double inverter having the features of claim 1 and by a method for operating a double inverter having the features of claim 9.

Advantageous embodiments of the invention are the subject of the subclaims.

A double inverter is proposed, comprising two inverter modules, comprising three half-bridges made of semiconductor switches, each with three phase connections, between which an inductive load, in particular an electrical machine having three stator windings, can be or is switched, wherein a switchable connection is provided between high-voltage potentials of the two inverter modules, which are connectable or connected to a battery, wherein a separating element designed as a semiconductor switch is arranged between the battery and one of the inverter modules and/or between the two inverter modules in one of the two high-voltage potentials of the connection. According to the invention, at least one of the semiconductor switches is designed as a parallel circuit comprising an IGBT and a MOSFET.

The MOSFET can be designed as a SiC MOSFET.

In one embodiment, the isolating element is designed as a semiconductor switch or as a mechanical switching element.

In one embodiment, the inverter module, which can be separated from the battery by means of the separating element, can be designed for low losses at high current intensity and low clock frequency, in particular in that its semiconductor switches can be designed as IGBTs, in particular with a freewheeling diode.

The other inverter module can be designed for low losses at low current and high clock frequency, in particular by having its semiconductor switches designed as MOSFETs, in particular SiC MOSFETs.

In one embodiment, the isolating element is optimized for low conduction losses and is designed in particular as a Si-IGBT, in particular with a freewheeling diode.

In one embodiment, the isolating element and/or at least some of the semiconductor switches (or all semiconductor switches) of the inverter module connected or connectable to the battery via the isolating element are each designed as a parallel circuit comprising an IGBT and a MOSFET.

In one embodiment, the isolating element is arranged in a negative high-voltage potential, wherein the semiconductor switches, designed as low-side switches, of the inverter module connected or connectable to the battery via the isolating element are each designed as a parallel circuit comprising an IGBT and a MOSFET.

Alternatively, the isolating element can be arranged in a positive high-voltage potential, wherein the semiconductor switches designed as high-side switches of the inverter module connected or connectable to the battery via the isolating element are each designed as a parallel circuit comprising an IGBT and a MOSFET.

Alternatively, a separating element is arranged in each of the two high-voltage potentials of the connection, whereby all semiconductor switches of the inverter module connected or connectable to the battery via the separating element are each designed as a parallel circuit comprising an IGBT and a MOSFET.

In one embodiment, each of the two separating elements can be configured for a respective current direction. In particular, one of the separating elements can be configured for one current direction and the other of the separating elements can be configured for an opposite current direction.

In one embodiment, the inverter module directly connected or connectable to the battery without the separating element can be designed as a three-level inverter made of semiconductor switches.

In one embodiment, the three-level inverter may be implemented in T-type topology, NCP topology, ANCP topology, or flying CAP topology.

In one embodiment, the inverter module connected or connectable to the battery via the separating element can be designed as a two-level inverter.

According to one aspect of the present invention, a method for operating a dual inverter as described above for operating an electric machine as the drive motor of an electrically powered vehicle is proposed, wherein the stator windings of the electric machine are each connected between one of the phase connections of one and the other of the two inverter modules. According to the invention, at lower requested speeds and/or lower requested powers of the vehicle, the electric machine is connected in a star connection by opening the isolating element and forming a star point by switching on the semiconductor switches, designed as low-side switches, of the inverter module separated from the battery by the isolating element, wherein a rotating field for operating the electric machine is generated by means of the other inverter module. At higher requested speeds and/or powers of the vehicle, the isolating element is switched on and a rotating field for operating the electric machine is generated by means of both inverter modules. In at least one, several or all of the semiconductor switches designed as a parallel circuit consisting of an IGBT and a MOSFET, the MOSFET is switched at small currents, while the IGBT is switched at large currents.

In one embodiment, it is provided that by controlling the semiconductor switches of the inverter module, which is designed as a three-level inverter and is not separated from the battery by the isolating element, different voltage levels are switched at the stator windings depending on the requested speeds and/or power of the vehicle.

The solution according to the invention makes it possible to increase efficiency when driving in the city, during cross-country journeys and/or during moderate driving on the motorway.

Embodiments of the invention are explained in more detail below with reference to drawings.

• 1 ein schematisches Schaltbild eines Doppelinverters, umfassend zwei Inverter-Module, zwischen denen eine elektrische Maschine geschaltet ist,
• 2 ein schematisches Schaltbild eines Doppelinverters mit einem Trennelement in einem negativen Hochvolt-Potential,
• 3 ein schematisches Schaltbild eines Doppelinverters mit einem Trennelement in einem positiven Hochvolt-Potential,
• 4 ein schematisches Schaltbild eines weiteren Ausführungsbeispiel eines Doppelinverters, umfassend zwei Inverter-Module, zwischen denen eine elektrische Maschine geschaltet ist,
• 5 ein schematisches Schaltbild des Doppelinverters bei Verschaltung der elektrischen Maschine in Sternschaltung in einem ersten Zustand,
• 6 ein schematisches Schaltbild des Doppelinverters bei Verschaltung der elektrischen Maschine in Sternschaltung in einem zweiten Zustand,
• 7 ein schematisches Schaltbild des Doppelinverters bei Verschaltung der elektrischen Maschine in Sternschaltung in einem dritten Zustand,
• 8 ein schematisches Schaltbild des Doppelinverters bei Verschaltung der elektrischen Maschine in Sternschaltung in einem vierten Zustand,
• 9 ein schematisches Schaltbild des Doppelinverters in einem fünften Zustand, und
• 10 ein schematisches Schaltbild des Doppelinverters in einem sechsten Zustand,
• 11 ein schematisches Schaltbild eines Doppelinverters, wobei einige Halbleiterschalter jeweils durch eine Parallelschaltung aus einem IGBT und einem MOSFET gebildet sind,
• 12 ein schematisches Schaltbild eines Doppelinverters, wobei die Low-Side-Schalter des zweiten Inverter-Moduls jeweils durch eine Parallelschaltung aus einem IGBT und einem MOSFET gebildet sind,
• 13 ein schematisches Schaltbild eines Doppelinverters, wobei die Low-Side-Schalter des zweiten Inverter-Moduls und das Trennelement jeweils durch eine Parallelschaltung aus einem IGBT und einem MOSFET gebildet sind,
• 14 ein schematisches Schaltbild eines Doppelinverters, wobei das Trennelement durch eine Parallelschaltung aus einem IGBT und einem MOSFET gebildet ist, und
• 15 ein schematisches Schaltbild eines Doppelinverters, wobei die Low-Side-Schalter des zweiten Inverter-Moduls und das Trennelement jeweils durch eine Parallelschaltung aus einem IGBT und einem MOSFET gebildet sind.

Showing:

• 1 a schematic diagram of a double inverter comprising two inverter modules between which an electrical machine is connected,
• 2 a schematic diagram of a double inverter with an isolating element in a negative high-voltage potential,
• 3 a schematic diagram of a double inverter with an isolating element in a positive high-voltage potential,
• 4 a schematic circuit diagram of a further embodiment of a double inverter, comprising two inverter modules between which an electrical machine is connected,
• 5 a schematic circuit diagram of the double inverter with the electrical machine connected in star connection in a first state,
• 6 a schematic diagram of the double inverter when the electrical machine is connected in star connection in a second state,
• 7 a schematic diagram of the double inverter when the electrical machine is connected in star connection in a third state,
• 8 a schematic diagram of the double inverter when the electrical machine is connected in star connection in a fourth state,
• 9 a schematic diagram of the double inverter in a fifth state, and
• 10 a schematic diagram of the double inverter in a sixth state,
• 11 a schematic diagram of a double inverter, where some semiconductor switches are each formed by a parallel connection of an IGBT and a MOSFET,
• 12 a schematic circuit diagram of a double inverter, wherein the low-side switches of the second inverter module are each formed by a parallel circuit of an IGBT and a MOSFET,
• 13 a schematic circuit diagram of a double inverter, wherein the low-side switches of the second inverter module and the isolating element are each formed by a parallel circuit of an IGBT and a MOSFET,
• 14 a schematic circuit diagram of a double inverter, wherein the isolating element is formed by a parallel circuit of an IGBT and a MOSFET, and
• 15 a schematic circuit diagram of a double inverter, wherein the low-side switches of the second inverter module and the isolating element are each formed by a parallel circuit of an IGBT and a MOSFET.

Corresponding parts are provided with the same reference numerals in all figures.

1 is a schematic circuit diagram of a dual inverter 1 comprising two inverter modules 2.1, 2.2, in particular B6 bridges, between which a load 3, in particular an electric machine 3, is connected, which has three stator windings L1, L2, L3. A switchable connection 4 is provided between the two inverter modules 2. The electric machine 3 can be designed as a drive machine of an electrically powered vehicle.

To increase efficiency when driving the vehicle, the electric machine 3 is not hard-wired to a star point or delta, but rather each stator winding L1, L2, L3 is designed to be accessible at both connection ends. On a first connection side of the three stator windings L1, L2, L3 is a first inverter module 2.1, comprising three half-bridges made up of semiconductor switches S1 to S6. On the other connection side of the three stator windings L1, L2, L3 is a second inverter module 2.2, comprising three half-bridges made up of semiconductor switches S7 to S12. Both inverter modules 2.1, 2.2 have two high-voltage potentials HV+, HV-, which are connected to a battery 5, for example, a high-voltage battery of the vehicle. A separating element S13, S14 for each current direction is arranged between the battery 5 and the second inverter module 2.2 and/or between the first inverter module 2.1 and the second inverter module 2.2 in at least one of the two high-voltage potentials HV+, HV-. This separating element S13, S14 can be implemented by semiconductor switches S13, S14 or by mechanical switching elements. 1 Two isolating elements S13, S14 are shown, so that either the upper semiconductor switches S7, S9, S11 (high-side switches) of inverter module 2.2 or the lower semiconductor switches S8, S10, S12 (low-side switches) of inverter module 2.2 can be used to form a star point. If only the star point representation of one of the two switch rows is provided, only one of the two isolating elements S13 or S14 is required.

When selecting semiconductors, it is advantageous if one of the inverter modules 2.1, 2.2, for example, inverter module 2.1, is designed for low losses at low current and high clock frequency (e.g., SiC MOSFETs), while the other of the inverter modules 2.1, 2.2, for example, inverter module 2.2, is designed for low losses at high current and low clock frequency (e.g., IGBT with freewheeling diode). The isolating elements S13 and S14 should also be optimized for low conduction losses, but can exhibit higher switching energies in terms of switching losses (e.g., Si IGBT with freewheeling diode).

2 is a schematic diagram of a double inverter 1, which differs from the one shown in 1 shown embodiment in that a separating element S14 is only provided in the negative high-voltage potential HV-.

In a first driving state, the electric machine 3 is connected in a star circuit. A star point is formed by switching on the semiconductor switches S8, S10, and S12 (low-side switches). The isolating element S14 interrupts the connection 4 to the capacitor C1 and the battery 5.

At lower speeds or lower power levels, it may be advantageous to connect the electric machine 3 at the star point. The first inverter module 2.1 assumes the role of the drive inverter to set a rotating field, allowing the electric machine 3 to operate, while the second inverter module 2.2, with the semiconductor switches S8, S10, S12, forms a star point of the electric machine 3 and, via the isolating element S14, disconnects the connection 4 to the energy storage device of the first inverter module 2.1. The isolating element S13 can be omitted if only the semiconductor switches S8, S10, S12 (low-side switches) are used for the connection to the star point.

In a second driving state, both ends of the stator windings L1, L2, and L3 are accessible, and the isolating element S14 is connected. The second inverter module 2.2 is used to apply the highest possible voltage to the stator windings L1 to L3 together with the first inverter module 2.1.

At higher speeds or power levels, it may be advantageous to apply the highest possible switching voltage to the stator windings L1, L2, and L3. For this purpose, the isolating element S14 is switched on. Thus, a voltage corresponding to the voltage of the battery 5 can be applied across each stator winding L1 to L3. Therefore, in this operating state, both inverter modules 2.1 and 2.2 are active and cycle to establish a rotating field, allowing the electric machine 3 to operate.

When operating with star point connection (first driving state), the voltage is, for example, only 1/3 or 2/3 of the voltage of battery 5.

If, in the second driving state, with the isolating element S14 closed, for example, the semiconductor switches S1 and S8 are switched on (closed) and the current in the stator winding L1 is positive (other phases were not considered here), then the current flows from the battery 5 via the semiconductor switch S1, the stator winding L1, the semiconductor switch S8 and the isolating element S14 back to the battery 5.

If, in the second driving state, with the separating element S14 closed, for example, the semiconductor switches S1 and S8 are open and the current in the stator winding L1 is positive (other phases were not considered here), then a freewheeling current flows from the stator winding L1 via the body diode of the semiconductor switch S7, the battery 5 and/or the capacitor C1 and the body diode of the semiconductor switch S2 back to the stator winding L1.

If, in the second driving state, with the isolating element S14 closed, for example, the semiconductor switch S1 is open and the semiconductor switch S8 is closed, and the current in the stator winding L1 is positive (other phases were not considered here), then a freewheeling current flows from the stator winding L1 via the semiconductor switch S8, the isolating element S14, and the body diode of the semiconductor switch S2 back to the stator winding L1. In this case, there is no feedback to battery 5. The AC component in the capacitor current is reduced.

3 is a schematic diagram of a double inverter 1, which differs from the one shown in 1 shown embodiment in that a separating element S13 is only provided in the positive high-voltage potential HV+.

In a first driving state, the electric motor 3 is connected in a star configuration. A star point is formed by switching on the semiconductor switches S7, S9, and S11 (high-side switches). The isolating element S13 interrupts the connection 4 to the capacitor C1 and the battery 5.

At lower speeds or lower power levels, it may be advantageous to connect the electric machine 3 at the star point. The first inverter module 2.1 assumes the role of the drive inverter to set a rotating field, allowing the electric machine 3 to operate, while the second inverter module 2.2, with the semiconductor switches S7, S9, S11, forms a star point of the electric machine 3 and, via the isolating element S13, disconnects the connection 4 to the energy storage device of the first inverter module 2.1. The isolating element S14 can be omitted if only the semiconductor switches S7, S9, S11 (low-side switches) are used for the connection to the star point.

In a second driving state, both ends of the stator windings L1, L2, and L3 are accessible, and the isolating element S13 is connected. The second inverter module 2.2 is used to apply the highest possible voltage to the stator windings L1 to L3 together with the first inverter module 2.1.

At higher speeds or power levels, it may be advantageous to apply the highest possible switching voltage to the stator windings L1, L2, and L3. For this purpose, the isolating element S13 is switched on. Thus, a voltage corresponding to the voltage of the battery 5 can be applied across each stator winding L1 to L3. Therefore, in this operating state, both inverter modules 2.1 and 2.2 are active and cycle to establish a rotating field, allowing the electric machine 3 to operate.

When operating with star point connection (first driving state), the voltage is, for example, only 1/3 or 2/3 of the voltage of battery 5.

If, in the second driving state, with the isolating element S13 closed, for example, the semiconductor switches S1 and S8 are switched on (closed) and the current in the stator winding L1 is positive (other phases were not considered here), then the current flows from the battery 5 via the semiconductor switch S1, the stator winding L1 and the semiconductor switch S8 back to the battery 5.

If, in the second driving state, with the isolating element S14 closed, for example, the semiconductor switches S1 and S8 are open and the current in the stator winding L1 is positive (other phases were not considered here), then a freewheeling current flows from the stator winding L1 via the body diode of the semiconductor switch S7, the isolating element S13, the battery 5 and/or the capacitor C1 and the body diode of the semiconductor switch S2 back to the stator winding L1.

If, in the second driving state, with the isolating element S13 closed, for example, the semiconductor switch S1 is open and the semiconductor switch S8 is closed and the current in the stator winding L1 is positive (other phases were not considered here), then a freewheeling current flows from the stator winding L1 via the semiconductor switch S8 and the body diode of the semiconductor switch S2 back to the stator winding L1. In this case, no feedback to the battery 5. The AC component in the capacitor current is reduced.

The procedure with the two driving states can be carried out with the double inverter 1 according to 1 be applied in the same way, whereby the additional isolating element S13, S14 should be closed. In this case, it is possible to choose whether the star point formation should be carried out by the high-side switches or the low-side switches, or by both.

4 is a schematic circuit diagram of a dual inverter 1 comprising two inverter modules 2.1, 2.2, between which a load 3, in particular an electric machine 3, is connected, which has three stator windings L1, L2, L3. A switchable connection 4 can be provided between the two inverter modules 2. The electric machine 3 can be designed as the drive motor of an electrically powered vehicle. A battery 5 with a battery voltage U_DC serves as the voltage source.

In one embodiment, at least one of the inverter modules 2.1, 2.2 can be configured as a three-level inverter. In the embodiment shown, the three-level inverter is embodied in a T-type topology, for example. However, an NPC, ANPC, or flying CAP topology can also be used instead. The other inverter module 2.1, 2.2 can be configured, for example, as a two-level inverter or as a B6 bridge.

The three-level inverter allows three additional voltage levels (line-to-line voltage) to be switched on the connection side of the electric motor (U_DC, 1/2 U_DC, 0, - 1/2 U_DC, -U_DC). These two additional switching voltages (1/2 U_DC and - 1/2 U_DC) allow a corner point in a motor characteristic map to be configured in additional steps.

To increase efficiency when driving the vehicle, the electric machine 3 is not hard-wired to a star point or delta, but rather each stator winding L1, L2, L3 is designed to be accessible at both connection ends. On a first connection side of the three stator windings L1, L2, L3 is a first inverter module 2.1, for example, the three-level inverter, comprising three half-bridges made of semiconductor switches S1 to S6, for example, field-effect transistors, in particular MOSFETs, which are connected between two high-voltage potentials HV+, HV- and have center taps, each of which forms a phase conductor. Furthermore, the first inverter module 2.1, designed as a three-level inverter, has three pairs of anti-serially connected semiconductor switches S14 to S19, for example field-effect transistors, in particular MOSFETs, which are connected on the one hand to one of the phase conductors and on the other hand to a center tap of a capacitive voltage divider consisting of two capacitors C2, C3. The capacitive voltage divider is connected between the two high-voltage potentials HV+, HV-.

On the other connection side of the three stator windings L1, L2, L3 there is a second inverter module 2.2, for example the two-level inverter, comprising three half-bridges made of semiconductor switches S7 to S12, for example IGBT with freewheeling diode, which are connected between two high-voltage potentials HV+, HV- and have center taps, each of which forms a phase conductor.

The two inverter modules 2.1, 2.2 are connected with their two high-voltage potentials HV+, HV- to the battery 5, for example a high-voltage battery, which can be located in a vehicle. A separating element S13 is arranged between the battery 5 and the second inverter module 2.2 and/or between the two inverter modules 2.1, 2.2 in at least one of the two high-voltage potentials HV+, HV-. This separating element S13 can be implemented by a semiconductor switch S13, for example an IGBT with a freewheeling diode, or by a mechanical switching element. 4 a separating element S13 is shown in the negative high-voltage potential HV-, so that the lower semiconductor switches S8, S10, S12 (low-side switches) of the second inverter module 2.2 can be used to form a star point. In another embodiment, the separating element S13 can be provided in the positive high-voltage potential HV+, so that the upper semiconductor switches S7, S9, S11 (high-side switches) of the second inverter module 2.2 can be used to form a star point. In another embodiment, an separating element S13 can be provided in both the negative high-voltage potential HV- and the positive high-voltage potential HV+, so that the upper semiconductor switches S7, S9, S11 (high-side switches) of the second inverter module 2.2 and/or the lower semiconductor switches S8, S10, S12 (low-side switches) of the B6 bridge 2.2 can be used to form a star point.

The isolating element S13 can be arranged alternatively in the positive high-voltage potential HV+ or in both high-voltage potentials HV+ and HV-. When located in the positive high-voltage potential HV+, the star point is formed by the upper switch row consisting of semiconductor switches S7, S9, and S11 of the second inverter module 2.2. If an isolating element S13 is placed in each of the two high-voltage potentials HV+ and HV-, the upper or lower switch row, or both simultaneously, can alternately represent the star point in the second inverter module 2.2.

When selecting components, it is advantageous to optimize the semiconductor switches S1 to S6, S14 to S19 in the first inverter module 2.1 for low switching losses (e.g., SiC MOSFET), while in the second inverter module 2.2, the priority is to keep the on-state losses at high currents low and the switching losses moderate, e.g., by selecting Si IGBTs as the semiconductor switches S7 to S12. The semiconductor switches S7 to S12 perform very few switching operations and only carry current when operated at higher power. Thus, a design for only low on-state losses at high currents is desirable, e.g., by using on-state optimized IGBTs.

The switchable isolating element S13 is used to represent a driving state with only one inverter module 2.1 (here the three-level inverter), with the second inverter module 2.2 (here the two-level inverter) creating the star point of the stator windings L1, L2, L3 at its connection point. The isolating element S13 is open, and the lower switch row of the second inverter module 2.2, consisting of the semiconductor switches S8, S10, S12, is switched on. In this operating state, the voltage applied to the connection terminals of the first inverter module 2.1 is divided in a ratio of 1/3 to 2/3, caused by the star connection of the stator windings L1, L2, L3. As soon as the isolating element S13 is closed, the following voltage levels can be applied across the stator windings L1, L2, L3: U_DC, ½ U_DC, 0, - ½ U_DC, -U_DC.

5 is a schematic circuit diagram of the double inverter 1 when the electrical machine 3 is connected in star connection in a first state.

In a first state, the electric machine 3 is connected in a star configuration. A star point is formed by switching on the semiconductor switches S8, S10, and S12 (low-side switches). The isolating element S13 interrupts the connection 4 to the capacitor C1 and the battery 5.

At lower speeds or lower power levels, it may be advantageous to connect the electric machine 3 at the star point. The first inverter module 2.1 assumes the role of the drive inverter to set a rotating field, allowing the electric machine 3 to operate, while the second inverter module 2.2, with the semiconductor switches S8, S10, S12, forms a star point of the electric machine 3 and, via the isolating element S13, separates the connection 4 to the energy storage device. 5 the first inverter module 2.1 provides the full voltage U_DC at the center taps of the half bridges. If, for example, the semiconductor switches S1, S4 and S6 of the first inverter module 2.1 are switched on and the current in the stator winding L1 is positive (towards the second inverter module 2.2) and in the stator windings L2, L3 is negative (towards the first inverter module 2.1), then a current I1 flows from the battery 5 via the semiconductor switch S1, the stator winding L1, the semiconductor switch S8, the star point, from there in two paths via the semiconductor switch S10, the stator winding L2 and the semiconductor switch S4 on the one hand and the semiconductor switch S12, the stator winding L3 and the semiconductor switch S6 on the other hand back to the battery 5. If, for example, the semiconductor switches S1 to S6 of the first inverter module 2.1 are opened and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I2 flows from the stator winding L1 via the semiconductor switch S8, the star point, from there in two paths via the semiconductor switch S10, the stator winding L2, and the body diode of the semiconductor switch S3 on the one hand, and the semiconductor switch S12, the stator winding L3, and the body diode of the semiconductor switch S5 on the other hand, through the battery 5 and the body diode of the semiconductor switch S2 back to the stator winding L1. The voltage across the stator winding L1 in this state is 2/3 U_DC.

6 is a schematic circuit diagram of the double inverter 1 when the electrical machine 3 is connected in star connection in a second state.

In the second state, as in 5 The electric machine 3 is connected in a star configuration. A star point is formed by switching on the semiconductor switches S8, S10, and S12 (low-side switches). The isolating element S13 interrupts the connection 4 to the capacitor C1 and the battery 5. The first inverter module 2.1 provides the full voltage U_DC at the connection terminals of the stator windings L1 to L3.

If, for example, the semiconductor switches S1, S4 and S6 of the first inverter module 2.1 are switched on and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I1 flows from the battery 5 via the semiconductor switch S1, the stator winding L1, the semiconductor switch S8, the star point, from there in two paths via the semiconductor switch S10, the stator winding L2 and the semiconductor switch S4 on the one hand and the semiconductor switch S12, the stator winding L3 and the semiconductor switch S6 on the other hand back to the battery 5. If, for example, in the first inverter module 2.1 the semiconductor switches S1 to S6 are opened and the semiconductor switches S16 and S18 are switched on and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I2 flows from the Stator winding L1 via semiconductor switch S8, the star point, from there in two paths via semiconductor switch S10, stator winding L2, semiconductor switch S16, and the body diode of semiconductor switch S17 on the one hand, and semiconductor switch S12, stator winding L3, semiconductor switch S18, and the body diode of semiconductor switch S19 on the other hand, through capacitor C3 and the body diode of semiconductor switch S2 back to stator winding L1. This charges capacitor C3. In this state, the voltage across stator winding L1 is 1/2*2/3 U_DC=1/3 U_DC.

7 is a schematic circuit diagram of the double inverter 1 when the electrical machine 3 is connected in star connection in a third state.

In the third state, as in the 5 and 6 The electric machine 3 is connected in a star configuration. A star point is formed by switching on the semiconductor switches S8, S10, and S12 (low-side switches). The isolating element S13 interrupts the connection 4 to the capacitor C1 and the battery 5. The first inverter module 2.1 provides half the voltage U_DC at the connection terminals of the stator windings L1 to L3.

If, for example, the semiconductor switches S15, S4 and S6 of the first inverter module 2.1 are switched on and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I1 flows from the battery 5 via the capacitor C2, the semiconductor switch S15, the body diode of the semiconductor switch S14, the stator winding L1, the semiconductor switch S8, the star point, from there in two paths via the semiconductor switch S10, the stator winding L2 and the semiconductor switch S4 on the one hand and the semiconductor switch S12, the stator winding L3 and the semiconductor switch S6 on the other hand back to the battery 5. If, for example, in the first inverter module 2.1 the semiconductor switches S1 to S6 and S14 to S19 are open and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I2 flows from the stator winding L1 via the semiconductor switch S8, the star point, from there in two Paths via the semiconductor switch S10, the stator winding L2, and the body diode of the semiconductor switch S3 on the one hand, and the semiconductor switch S12, the stator winding L3, and the body diode of the semiconductor switch S5 on the other hand, through the battery 5 and the body diode of the semiconductor switch S2 back to the stator winding L1. This charges the battery 5. In this state, the voltage across the stator winding L1 is ½*2/3 U_DC=1/3 U_DC.

8 is a schematic circuit diagram of the double inverter 1 when the electrical machine 3 is connected in star connection in a fourth state.

In the fourth state, as in the 5 to 7 The electric machine 3 is connected in a star circuit. A star point is formed by switching on the semiconductor switches S8, S10, and S12 (low-side switches). The isolating element S13 interrupts the connection 4 to the capacitor C1 and the battery 5.

The first inverter module 2.1 provides half the voltage U_DC at the connection terminals of the stator windings L1 to L3.

If, for example, the semiconductor switches S15, S4 and S6 of the first inverter module 2.1 are switched on and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I1 flows from the battery 5 via the capacitor C2, the semiconductor switch S15, the body diode of the semiconductor switch S14, the stator winding L1, the semiconductor switch S8, the star point, from there in two paths via the semiconductor switch S10, the stator winding L2 and the semiconductor switch S4 on the one hand and the semiconductor switch S12, the stator winding L3 and the semiconductor switch S6 on the other hand back to the battery 5. If, for example, in the first inverter module 2.1 the semiconductor switches S1 to S6, S14, S17 and S19 are opened and the semiconductor switches S15, S16 and S18 are switched on and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I2 flows from the Stator winding L1 via semiconductor switch S8, the star point, from there in two paths via semiconductor switch S10, stator winding L2, semiconductor switch S16, and the body diode of semiconductor switch S17 on the one hand, and semiconductor switch S12, stator winding L3, semiconductor switch S18, and the body diode of semiconductor switch S19 on the other hand, through semiconductor switch S15 and the body diode of semiconductor switch S14 back to stator winding L1. The voltage across stator winding L1 in this state is 1/2*2/3 U_DC=1/3 U_DC.

9 is a schematic diagram of the double inverter 1 in a fifth state.

In a fifth state, both ends of the stator windings L1, L2, and L3 are accessible, and the isolating element S13 is connected. The second inverter module 2.2 is used to apply the highest possible voltage to the stator windings L1 to L3 together with the first inverter module 2.1.

At higher speeds or power levels, it may be advantageous to apply the highest possible switching voltage to the stator windings L1, L2, and L3. For this purpose, the isolating element S13 is switched on. Thus, a voltage corresponding to the voltage U_DC of the battery 5 can be applied across each stator winding L1 to L3. Therefore, in this operating state, both inverter modules 2.1 and 2.2 are active and cycle to establish a rotating field, allowing the electric machine 3 to operate.

If, for example, the semiconductor switches S1, S4 and S6 of the first inverter module 2.1 and the semiconductor switch S8 of the second inverter module 2.2 are switched on and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I1 flows from the battery 5 via the semiconductor switch S1, the stator winding L1, the semiconductor switch S8 and the isolating element S13 back to the battery 5. If, for example, in the first inverter module 2.1 the semiconductor switches S1 to S6 are open and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I2 flows from the stator winding L1 via the semiconductor switch S8, the isolating element S13 and the body diode of the semiconductor switch S2 back to the stator winding L1. The voltage across the stator winding L1 in this state is U_DC.

10 is a schematic diagram of the double inverter 1 in a sixth state.

In a sixth state, both ends of the stator windings L1, L2, and L3 are accessible, and the isolating element S13 is connected. The second inverter module 2.2 is used to apply the highest possible voltage to the stator windings L1 to L3 together with the first inverter module 2.1.

In this operating state, both inverter modules 2.1, 2.2 are active and clock to set a rotating field, which allows the electric machine 3 to be operated.

If, for example, the semiconductor switches S15, S4 and S6 of the first inverter module 2.1 and the semiconductor switch S8 of the second inverter module 2.2 are switched on and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I1 flows from the battery 5 via the capacitor C2, the semiconductor switch S15, the body diode of the semiconductor switch S14, the stator winding L1, the semiconductor switch S8 and the isolating element S13 back to the battery 5. If, for example, in the first inverter module 2.1 the semiconductor switches S1 to S6 are open and the current in the stator winding L1 is positive and in the stator windings L2, L3 is negative, then a current I2 flows from the stator winding L1 via the semiconductor switch S8, the isolating element S13 and the body diode of the semiconductor switch S2 back to the stator winding L1. The voltage across the stator winding L1 in this state is ½ U_DC.

In a further embodiment, the first inverter module 2.1 can be designed as a two-level inverter and the second inverter module 2.2 as a three-level inverter. In a further embodiment, both inverter modules 2.1, 2.2 can be designed as three-level inverters.

According to another embodiment, IGBTs and their freewheeling diodes can be replaced by a parallel circuit consisting of an IGBT and a MOSFET, for example, an IGBT and a SiC MOSFET (including its body diode). This allows for a reduction in conduction losses at low currents, since the ohmic behavior of the (SiC) MOSFET represents the lower resistance compared to the behavior of the IGBT with an (almost) constant voltage drop. The design of the components can be optimized such that the (SiC) MOSFET is used for operation at low currents, while the IGBT is switched at high currents.

11 is a schematic diagram of a double inverter 1, similar to the one in 2 shown double inverter 1, wherein all semiconductor switches S7 to S13 designed as IGBTs with freewheeling diodes are each replaced by a parallel circuit consisting of an IGBT and a MOSFET, in particular a SiC MOSFET. The parallel connection of the semiconductor switches S8, S10, S12 (low-side switches) of the second inverter module 2.2 leads to optimization when driving with a closed star point, i.e. with small currents and low to medium engine speeds (for example, city traffic and cross-country driving). The semiconductor switches S7, S9, S11 (high-side switches) of the second inverter module 2.2 are not engaged in these operating states. The semiconductor switch S13 (isolating element S13) is permanently open, i.e. permanently blocking, and thus also current-free. It follows that only for optimization at low currents and moderate speeds can a combination of IGBT and (SiC-) MOSFET be useful for the semiconductor switches S8, S10 and S12.

The isolating element S13 can alternatively be arranged in the positive high-voltage potential HV+. Likewise, an isolating element S13 can be provided in both the positive high-voltage potential HV+ and the negative high-voltage potential HV-.

12 is a schematic diagram of a double inverter 1, similar to the one in 2 and 11 shown double inverter 1, wherein only the semiconductor switches S8, S10, S12 (low-side switches) of the second inverter module (2.2), which are designed as IGBTs with freewheeling diodes, are each replaced by a parallel circuit comprising an IGBT and a MOSFET, in particular a SiC MOSFET. This represents an optimization for operation with a closed star point and low motor currents. The remaining 2 Semiconductor switches S7, S9, S11, S13 designed as IGBTs with freewheeling diodes can be retained or replaced by IGBTs without freewheeling diodes.

Alternatively, the semiconductor switches S7, S9, and S11 can also be used to form the star point. In this case, a MOSFET, in particular a SiC MOSFET, must be connected in parallel with each of these semiconductor switches S7, S9, and S11, which are represented as IGBTs, and the isolating element S13 for breaking the connection 4 between the two inverter modules 2.1 and 2.2 must be arranged at the positive high-voltage potential HV+. In this case, the semiconductor switches S8, S10, and S12 (low-side switches) can be designed as IGBTs with or without a freewheeling diode.

13 is a schematic diagram of a double inverter 1, similar to the one in 2 , 11 and 12 shown double inverter 1, wherein only the semiconductor switches S8, S10, S12 (low-side switches) of the second inverter module (2.2) designed as IGBTs with freewheeling diodes and the isolating element S13 are each replaced by a parallel circuit comprising an IGBT and a MOSFET, in particular a SiC MOSFET.

Considering the application of constant highway driving, the circuit is in the operating state with an open star point. The full DC link voltage is applied across each starter winding L1, L2, and L3 via both inverter modules 2.1 and 2.2. A current flow through the isolating element S13 is necessary to supply the second inverter module 2.2. As long as the vehicle is driving with low motor currents at higher speeds (e.g., highway driving, moderate speed), the currents through the isolating element S13 are also low. Therefore, for this application, the losses for moderate highway driving can be reduced by forming the isolating element S13 as a parallel circuit consisting of an IGBT and a (SiC) MOSFET. This can increase efficiency.

Alternatively, the semiconductor switches S7, S9, and S11 can also be used to form the star point. In this case, a MOSFET, in particular a SiC MOSFET, must be connected in parallel with each of these semiconductor switches S7, S9, and S11, which are represented as IGBTs, and the isolating element S13 for breaking the connection 4 between the two inverter modules 2.1 and 2.2 must be arranged at the positive high-voltage potential HV+. In this case, the semiconductor switches S8, S10, and S12 (low-side switches) can be designed as IGBTs with or without a freewheeling diode.

14 is a schematic diagram of a double inverter 1, similar to the one in 2 , shown double inverter 1, wherein only the isolating element S13, designed as an IGBT with a freewheeling diode, is replaced by a parallel circuit comprising an IGBT and a MOSFET, in particular a SiC MOSFET. The remaining 2 Semiconductor switches S7, S9, S11, S13 designed as IGBTs with freewheeling diodes can be retained or replaced by IGBTs without freewheeling diodes.

If the focus of efficiency optimization is only on moderate highway driving, the semiconductor switches S8, S10 and S12 (low-side switches) can remain as IGBTs and the isolating element S 13 can be constructed from the parallel connection of an IGBT and a (SiC) MOSFET.

Alternatively, the semiconductor switches S7, S9, and S11 can also be used to form the star point. In this case, the isolating element S13 for breaking the connection 4 between the two inverter modules 2.1 and 2.2 must be arranged at the positive high-voltage potential HV+.

15 is a schematic diagram of a double inverter 1, similar to the one in 4 shown double inverter 1, where the 4 The semiconductor switches S8, S10, S12, and S13, designed as IGBTs with freewheeling diodes, are each replaced by a parallel circuit comprising an IGBT and a MOSFET, in particular a SiC MOSFET. The parallel connection of the semiconductor switches S8, S10, and S12 (low-side switches) of the second inverter module 2.2 results in optimization when driving with a closed star point, i.e., with small currents and low to medium engine speeds (e.g., city traffic and cross-country driving). The semiconductor switches S7, S9, and S11 (high-side switches) of the second inverter module 2.2 are not engaged in these operating states. The semiconductor switch S13 (isolating element S13) is permanently open, i.e., permanently blocking, and thus also current-free.

A parallel circuit of IGBT and (SiC) MOSFET for the isolating element S13 has a positive effect on efficiency when operating with an open star point and a closed isolating element S13. As long as the DC currents across the isolating switch S13 are low, the (SiC) MOSFET represents the significantly lower resistance and This reduces losses at low DC currents. The application here is, for example, highway driving with moderate motor currents.

Of course, it is also possible to implement only the semiconductor switches S8, S10 and S12 by a parallel connection of IGBT and (SiC-) MOSFET (optimization only for city and intercity driving) or to implement only the isolating element S13 by a parallel connection of IGBT and (SiC-) MOSFET (optimization only for motorway driving).

Alternatively, the isolating element S13 can also be arranged at the positive high-voltage potential HV+. In this case, the upper semiconductor switches S7, S9, and S11 (high-side switches) are designed as a parallel circuit of IGBT and (SiC) MOSFET.

Likewise, a separator S13 can be provided in both the positive high-voltage potential HV+ and the negative high-voltage potential HV-. In this case, the upper semiconductor switches S7, S9, S11 (high-side switches) and the lower semiconductor switches S8, S10, S12 (low-side switches) are designed as a parallel circuit of IGBT and (SiC) MOSFET.

List of reference symbols

1

Double inverter

2.1, 2.2

Inverter module

3

Load, electrical machine

4

Connection

5

battery

C1, C2, C3

capacitor

HV+, HV-

High voltage potential, HV potential

L1, L2, L3

Stator winding

S1 to S19

semiconductor switches

S13, S14

Separating element

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10 2022 132 370 A1 [0002]

Claims (10)

Double inverter (1), comprising two inverter modules (2.1, 2.2), comprising three half-bridges made of semiconductor switches (S1 to S19), each with three phase connections, between which an inductive load (3), in particular an electrical machine (3) is switchable or connected, which has three stator windings (L1, L2, L3), wherein a switchable connection (4) is provided between high-voltage potentials (HV+, HV-) of the two inverter modules (2.1, 2.2), which are connectable or connected to a battery (5), wherein a separating element (S13) designed as a semiconductor switch (S13) is arranged between the battery (5) and one of the inverter modules (2.1, 2.2) and/or between the two inverter modules (2.1, 2.2) in one of the two high-voltage potentials (HV+, HV-) of the connection (4), characterized in that at least one of the semiconductor switches (S1 to S19) is designed as a parallel circuit comprising an IGBT and a MOSFET. Double inverter (1) after Claim 1 , characterized in that the MOSFET is designed as a SiC MOSFET. Double inverter (1) after Claim 1 or 2 , characterized in that the separating element (S13) and/or at least some of the semiconductor switches (S7 to S12) or all semiconductor switches (S7 to S12) of the inverter module (2.2) connected or connectable to the battery (5) via the separating element (S13) are/are each designed as a parallel circuit comprising an IGBT and a MOSFET. Double inverter (1) after Claim 3 , characterized in that - the isolating element (S13) is arranged in a negative high-voltage potential (HV-), wherein the semiconductor switches (S8, S10, S12) of the inverter module (2.2) connected or connectable to the battery (5) via the isolating element (S13), which are designed as low-side switches, are each designed as a parallel circuit comprising an IGBT and a MOSFET, or - the isolating element (S13) is arranged in a positive high-voltage potential (HV+), wherein the semiconductor switches (S7, S9, S11) of the inverter module (2.2) connected or connectable to the battery (5) via the isolating element (S13), which are designed as high-side switches, are each designed as a parallel circuit comprising an IGBT and a MOSFET, or - a isolating element (S13) is arranged in each of the two high-voltage potentials (HV+, HV-) of the connection (4), wherein all semiconductor switches (S7 to S12) of the inverter module (2.2) connected or connectable to the battery (5) via the separating element (S13) are each designed as a parallel circuit comprising an IGBT and a MOSFET. Double inverter (1) after Claim 4 , characterized in that each of the two separating elements (S13) is configured for one current direction. Double inverter (1) according to one of the preceding claims, characterized in that the inverter module (2.1) which is or can be connected directly to the battery (5) without the separating element (S13) is designed as a three-level inverter comprising semiconductor switches (S1 to S6, S14 to S19). Double inverter (1) after Claim 6 , characterized in that the three-level inverter is designed in T-type topology, in NCP topology, in ANCP topology or in flying CAP topology. Double inverter (1) according to one of the preceding claims, characterized in that the inverter module (2.2) connected or connectable to the battery (5) via the separating element (S13) is designed as a two-level inverter. Method for operating a double inverter (1) according to one of the preceding claims for operating an electric machine (3) as a drive machine of an electrically driven vehicle, wherein the stator windings (L1, L2, L3) of the electric machine (3) are each connected between one of the phase connections of one and the other of the two inverter modules (2.1, 2.2), characterized in that at lower requested speeds and/or lower requested powers of the vehicle, the electric machine (3) is connected in a star connection by opening the isolating element (S13) and a star point is formed by switching on the semiconductor switches (S8, S10, S12) designed as low-side switches of the inverter module (2.1, 2.2) separated from the battery (5) by the isolating element (S13), wherein a rotating field for operating the electric machine (3) is generated by means of the other inverter module (2.1), wherein at higher requested speeds and/or powers of the vehicle, the isolating element (S13) is switched through and a rotating field for operating the electrical machine (3) is generated by means of both inverter modules (2.1, 2.2), wherein in at least one, several or all of the semiconductor switches (S1 to S19) designed as a parallel circuit comprising an IGBT and a MOSFET, the MOSFET is switched at low currents, while the IGBT is switched at high currents. Procedure according to Claim 9 , characterized in that by controlling the Semiconductor switches (S1 to S6, S14 to S19) of the inverter module (2.1, 2.2), which is designed as a three-level inverter and is not separated from the battery (5) by the isolating element (S13), switch different voltage levels at the stator windings (L1, L2, L3) depending on the requested speeds and/or power of the vehicle.

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