DE102022134477A1 - Power module, electrical power converter and electric drive for a means of transport - Google Patents

Abstract

Power module (1) comprising at least one arrangement (2, 2') of a plurality of dies (2a-h), each of which forms a transistor with a switching path, each die (2a-h) having a first terminal (3), a second terminal (4) and a control terminal (5), the switching path being formed between the first terminal (3) and the second terminal (4) and being switchable as a function of a voltage at the control terminal (5) and the second terminal (4), the transistors being connected in parallel by connecting the first terminals (3) to one another and connecting the second terminals (4) to one another, the at least one arrangement (2, 2') comprising a shielding structure (13) which at least partially covers at least two of the dies (2a-h), the shielding structure (13) comprising or consisting of one or more materials selected from a group consisting of a nickel-zinc-based ferrite, a soft ferromagnetic nickel-iron alloy and an electrical steel.

Description

Field of the invention

The present invention relates to a power module comprising at least one arrangement of a plurality of dies, each forming a transistor with a switching path, each die having a first terminal, a second terminal and a control terminal, the switching path being formed between the first terminal and the second terminal and being switchable depending on a voltage at the control terminal and the second terminal, the transistors being connected in parallel by the first terminals being connected to one another and the second terminals being connected to one another.

The invention also relates to an electrical power converter and an electric drive for a means of transport, for example for a vehicle or for a bicycle.

Background of the invention

I. Kovacevic-Badstübner, U. Grossner, D. Popescu and B. Popescu, “Transient Stability Analysis of Discrete and Multi-chip Power Semiconductor Packages”, 2021 33rd International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2021, pp. 391-394 , disclose parallel-connected power devices based on 650V SiC power MOSFETs and discuss high-frequency oscillations that occur during fast switching operations.

With the increasing power requirements of traction inverters for electric transport, the parallel connection of several dies has proven to be necessary in order to cope with the corresponding current and loss densities. However, the parallel connection of the dies leads to very complex resonance systems with characteristic feedback loops. Corresponding oscillations are to be expected in the VHF band, especially above 100 MHz, and can trigger different failure mechanisms in a structure of the control connections of the dies.

In order to reduce the corresponding couplings in such feedback loops, I. Kasko, SE Berberich, M. Spang and S. Oehling, “SiC MOS Power Module in Direct Pressed Die Technology and some Challenges for Implementation,” 2020 32nd International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2020, pp. 364-367 , proposed to increase the internal gate resistance of parallel SiC-MOS. However, increasing the resistance at the control terminal has the disadvantage that the achievable switching speed of the power module decreases and internal changes to the dies are required. In addition, the integration of individual gate series resistors increases the complexity of the module assembly process and the space required for the power module, thus deteriorating the reliability and power density of the electrical power converter.

Furthermore, the EN 10 2019 202 728 A1 It is known to provide half-bridges of semiconductor switches with a plate-shaped structure made of electrically conductive material. The plate-shaped structure is mounted at a distance from the half-bridge in order to reduce intermediate circuit inductance by inducing eddy currents in the plate-shaped structure.

Furthermore, the US 2003/0011057 A1 a semiconductor device having a semiconductor element and a bonding wire connecting the semiconductor element to an electrode. A sheet member is disposed over the bonding wire. A molding resin member covers the electrode, the semiconductor element and the bonding wire and buries the sheet member. The sheet member reduces vibrations of the molding resin member.

Brief description of the invention

An object of the invention is to improve the operation of a power module with parallelized dies, in particular with regard to reducing VHF oscillations.

According to the invention, this object is achieved by a power module as described above, in which the at least one arrangement comprises a shielding structure which at least partially covers at least two of the dies, wherein the shielding structure comprises or consists of one or more materials which are selected from a group consisting of a nickel-zinc-based ferrite, a soft ferromagnetic nickel-iron alloy and an electrical steel.

The power module according to the invention comprises at least one arrangement of several dies. Each die forms a transistor with a switching path. Each die has a first terminal, a second terminal and a control terminal. The switching path is formed between the first and the second terminal. The switching path can be switched depending on a voltage at the control terminal and the second terminal. The Transistors are connected in parallel by connecting the first terminals together and connecting the second terminals together. The at least one arrangement further comprises a shielding structure. The shielding structure at least partially covers at least two of the dies. The shielding structure comprises or consists of one or more materials. The material or materials are selected from a group. The group consists of a nickel-zinc based ferrite, a soft ferromagnetic nickel-iron alloy and an electrical steel.

The invention is based on the consideration of reducing VHF oscillations caused by inductive feedback loops when paralleling the dies by providing a shielding structure to influence the magnetic coupling between the first and second terminals and a control terminal loop and/or by damping the feedback loops. Nickel-zinc-based ferrites offer suitable high-frequency loss properties for damping the feedback loops. In addition, it has been found that a shielding structure made of or containing a soft ferromagnetic nickel-iron alloy and/or electrical steel also leads to a significant reduction in the VHF oscillation amplitudes, although these materials are not normally known for their high-frequency properties. Advantageously, the power module according to the invention enables the reduction of the VHF oscillations, in particular without affecting the control terminal internal resistances and without reducing the maximum switching speed of the power module.

The group may be restricted to consist only of the nickel-zinc based ferrite, or only of the nickel-iron based soft ferromagnetic alloy, or only of the electrical steel, or only of the nickel-zinc based ferrite and the nickel-iron based soft ferromagnetic alloy, or only of the nickel-zinc based ferrite and the electrical steel, or only of the nickel-iron based soft ferromagnetic alloy and the electrical steel.

The number of dies can be at least two, preferably at least four, particularly preferably at least six. The transistor can be an insulated gate bipolar transistor (IGBT). In this case, the first terminal can be a collector terminal, the second terminal an emitter terminal and the control terminal a gate terminal. Alternatively, the transistor can be a metal oxide semiconductor field effect transistor (MOSFET), preferably based on silicon carbide (SiC), or a high electron mobility transistor (HEMT), in particular based on gallium nitride (GaN). In MOSFETs and HEMTs, the first terminal can be a drain terminal, the second terminal a source terminal and the control terminal a gate terminal. The transistor is preferably configured such that it blocks voltages of at least 400 V, preferably at least 800 V, particularly preferably at least 1200 V, via the switching path. However, the invention can also be applied to low-voltage power modules, e.g. in 48-volt systems, where the transistor is configured to block voltages of at least 50 V.

In detail, electrical connections between the dies can form a resonant circuit with one or more resonant frequencies of at least 100 MHz and feedback loops that establish an inductive coupling between the second terminals on the one hand and the first terminals and/or control terminals on the other hand. The shielding structure can then be configured to reduce the inductive coupling. The shielding structure can therefore specifically be set up to reduce the inductive coupling between feedback loops connected to the first and second terminals (output loops) and/or feedback loops connected to the control terminal and the second terminal (input loops) in the aforementioned frequency range. In particular, the minimum resonant frequency can be between 100 MHz and 1 GHz.

$\underset{\_}{\mu }={\mu }_0\cdot \left({\mu }_r^{\text{'}}-j\cdot {\mu }_r^{"}\right)$

wobei µ₀ die magnetische Vakuumpermeabilität bezeichnet, ${\mu }_r^{\text{'}}$

den Realteil der relativen Permeabilität bezeichnet, ${\mu }_r^{"}$

den Imaginärteil der relativen Permeabilität bezeichnet und j die Imaginäreinheit bezeichnet.The nickel-zinc-based ferrite preferably has a complex permeability with a real part and an imaginary part. The complex permeability µ of the nickel-zinc-based ferrite can thus be expressed as $$

$\underset{\_}{\mu }={\mathrm{<figure-callout\; id="0"\; label="\mu "\; filenames="DE102022134477A1\_0011.png,DE102022134477A1\_0012.png"\; state="\{\{state\}\}">\mu </figure-callout>}}_0\cdot \left({\mu }_r^{\text{'}}-j\cdot {\mu }_r^{"}\right)$

where µ ₀ is the magnetic vacuum permeability, ${\mu }_r^{\text{'}}$

the real part of the relative permeability, ${\mu }_r^{"}$

denotes the imaginary part of the relative permeability and j denotes the imaginary unit.

Desirably, a maximum of the imaginary part lies in a frequency range between 10 MHz and 1 GHz, preferably between 100 MHz and 1 GHz. If the maximum of the imaginary part lies within or near the expected oscillation frequencies, a strong damping effect on the oscillations is obtained, so a nickel-zinc based ferrite with a maximum in this range is favored.

Alternatively or additionally, at a frequency of 100 MHz, preferably 50 MHz, more preferably 10 MHz, the real part of the complex permeability is reduced compared to its value at frequencies close to zero. In particular, the real part is reduced by a factor of two, preferably by a factor of 10. It has been found that a relatively high value of the real part can even amplify the oscillations since the magnetic flux linkage and feedback increase accordingly. Therefore, it is preferable to choose a nickel-zinc based ferrite whose real part of the complex permeability already decreases at the above-mentioned frequency. It should be noted that there is a relationship between the real part of the complex permeability of the ferrite and a corner frequency according to Snoek's law, which states that the higher the real part of the complex permeability, the lower the corner frequency. It has been found that suitable values of the real part of the complex for frequencies approaching zero permeability are below 300, preferably 100, particularly preferably 30.

Overall, it is desirable to choose a nickel-zinc based ferrite with a high value of the imaginary part of the complex permeability and at the same time a low value of the real part of the complex permeability to achieve high damping efficiency.

The soft magnetic nickel-iron alloy may be mu-metal or permalloy. The nickel-iron alloy may contain A wt% nickel, B wt% iron and C wt% of a metal, where A+B+C ≤ 100, 75 ≤ A ≤ 80, 15 ≤ B ≤ 20, 2 ≤ C ≤ 5 and the metal is one or more metals selected from the group consisting of copper, chromium, molybdenum and cobalt. Such an alloy is commercially available but is typically not used for high frequency or EMI applications.

The electrical steel may be a silicon steel, particularly one that is not grain oriented. The electrical steel may comply with the EN 10106:2015 or the EN 10107:2014 standard. Such a steel is usually used as sheet material for transformer or motor applications, but not for applications in the VHF range or above.

In general, the shielding structure can be plate-shaped. This means that the shielding structure can cover the at least two dies in two spatial directions and can have a small thickness in the vertical spatial direction. Typically, the shielding structure has a thickness of less than 5 mm, preferably less than 2 mm, particularly preferably less than 1 mm or even less than 0.5 mm.

In general, the at least one arrangement can further comprise an electrically conductive first pad to which the second terminals are connected. The power module can also comprise an electrically conductive second pad to which the first terminals are connected and/or an electrically conductive track to which the control terminals are connected and/or an electrically conductive further pad of the power module to which further pad Kelvin terminals of the dies are connected. Of course, the dies can have further terminals, such as terminals for current measurement.

According to a first preferred embodiment of the power module according to the invention, the shielding structure does not cover the die that is the closest distance from the first pad. In this case, a die that is located near the first pad may not be covered because it only forms a relatively small feedback loop with respect to the second pad or the conductor track. Alternatively or additionally, the shielding structure does not cover the die that is the closest distance from the further pad. In this case, a die that is located near the further pad may not be covered because it only forms a relatively small feedback loop with respect to the conductor track. By omitting the covering of selected dies, material for the shielding structure can advantageously be saved.

According to a second preferred embodiment of the power module according to the invention, the shielding structure covers each die at least partially. By covering all dies, a high attenuation efficiency can be achieved.

With regard to the power module according to the invention, it is further preferred that the shielding structure completely covers the at least two dies. By completely covering the respective dies, a high attenuation efficiency can also be achieved.

The power module according to the invention can further comprise a carrier on which the dies are mounted, wherein the at least two dies are arranged between the carrier and the shielding structure. The carrier can be made of ceramic, using a direct bonded copper substrate (DBC), a direct bonded aluminum substrate (DBA) or a soldered active metal substrate (AMB). Alternatively, the carrier can also be made of metal with a dielectric coating thereon. Such a carrier can realize an insulated metal substrate (IMS).

The power module according to the invention can also comprise a single body formed from electrically insulating molding material, the body covering the dies and/or the electrical connections, e.g. wire connections, between the dies. The body can be used together with the carrier by overmolding it. The carrier can also be omitted so that the body covers or embeds the dies and the electrical connection. This allows a TML (transfer molded lead frame) design to be realized. The body can also cover or embed the pads.

Preferably, the body embeds the shielding structure. This allows the position of the shielding structure to be fixed in relation to the dies or connections in order to provide stable damping properties.

The at least one arrangement may further comprise a support structure supporting the shielding structure. The support structure may provide a defined distance between the dies and the shielding structure, thereby locating the shielding structure at a position where good attenuation properties can be achieved. It should be noted that the choice of the distance depends on various design details of the power module and should be made based on simulations or experiments.

In detail, the support structure can be mounted on the carrier. Furthermore, the support structure can be a frame on which the shielding structure is arranged, or a plurality of domes, each of which selectively supports the shielding structure. In addition, the support structure can be electrically connected to the shielding structure. Thus, the support structure can be realized using different geometries, which facilitates application to a wide variety of power module designs.

Furthermore, the support structure can be electrically insulating. This can avoid the creation of electrical connections between the shielding structure and other electrically conductive components. However, it is possible for the shielding structure to be connected to a suitable voltage potential of the power module, e.g. via the support structure, in order to additionally shield an electrical flow generated by switching operations of the dies in order to reduce electromagnetic emissions.

Preferably, a first arrangement and a second arrangement are present, wherein the first terminals of the first arrangement are connected to the second terminals of the second arrangement to form a half-bridge.

According to a further aspect, the present invention relates to a power module comprising at least one arrangement of a plurality of dies, each of which forms a transistor with a switching path, each die having a first terminal, a second terminal and a control terminal, the switching path being formed between the first terminal and the second terminal and being switchable depending on a voltage at the control terminal and the second terminal, the transistors being connected in parallel by the first terminals being connected to one another and the second terminals being connected to one another, the arrangement comprising a shielding structure that at least partially covers at least two of the dies, electrical connections between the dies forming a resonant circuit with one or more resonant frequencies of at least 100 MHz and feedback loops that form an inductive coupling between the second terminals on the one hand and the first terminals and/or control terminals on the other hand, the shielding structure being configured to reduce the inductive coupling. All of the above statements apply analogously to this aspect, so that the corresponding advantages can also be achieved here.

The present invention further relates to an electrical power converter, comprising: a DC connection for a direct voltage; an AC connection with several phase conductors for an alternating voltage; and a power section comprising a plurality of switching elements connected to form a half-bridge for each phase conductor, each half-bridge being connected between the DC connection and each phase conductor being connected to a central tap between the switching elements of one of the half-bridges; each switching element or each half-bridge being formed by a power module according to the invention.

The half bridges can be connected to two lines of the DC connection. Of course, there are other ways to connect the half bridges to the DC connection.

The present invention further relates to an electric drive for a means of transport, for example for a vehicle or a bicycle, comprising an electric machine which is designed to drive the means of transport, and an electric power converter according to the invention, wherein the electric machine is connected to the AC connection of the electric power converter to supply the electrical machine with alternating voltage.

Short description of the drawings

• 1 eine Teildraufsicht einer ersten Ausführungsform eines erfindungsgemäßen Leistungsmoduls;
• 2 eine Draufsicht des Leistungsmoduls gemäß der ersten Ausführungsform;
• 3 eine Querschnittsansicht des Leistungsmoduls gemäß der ersten Ausführungsform;
• 4 eine Draufsicht einer zweiten Ausführungsform des erfindungsgemäßen Leistungsmoduls;
• 5 Diagramme einer Gate-Source-Spannung, einer Drain-Source-Spannung und eines Drain-Source-Stroms über der Zeit und der Gate-Source-Spannung über der Frequenz für ein Leistungsmodul ohne Abschirmstruktur;
• 6 Diagramme einer Gate-Source-Spannung, einer Drain-Source-Spannung und eines Drain-Source-Stroms über der Zeit sowie der Gate-Source-Spannung über der Frequenz für ein Leistungsmodul mit einer Abschirmstruktur aus Mangan-Zink-Ferrit;
• 7 Diagramme einer Gate-Source-Spannung, einer Drain-Source-Spannung und eines Drain-Source-Stroms über der Zeit und der Gate-Source-Spannung über der Frequenz für ein erfindungsgemäßes Leistungsmodul mit einer Abschirmstruktur aus einer weichferromagnetischen Nickel-Eisen-Legierung;
• 8 Diagramme einer Gate-Source-Spannung, einer Drain-Source-Spannung und eines Drain-Source-Stroms über der Zeit und der Gate-Source-Spannung über der Frequenz für ein erfindungsgemäßes Leistungsmodul mit einer Abschirmstruktur aus Elektrostahl;
• 9 ein Blockdiagramm einer Ausführungsform eines erfindungsgemäßen elektrischen Leistungswandlers; und
• 10 eine Prinzipzeichnung eines Elektrofahrzeugs mit einer Ausführungsform eines erfindungsgemäßen elektrischen Antriebs.

Further details and advantages of the invention are disclosed below, with reference to the drawings, which show schematically:

• 1 a partial plan view of a first embodiment of a power module according to the invention;
• 2 a plan view of the power module according to the first embodiment;
• 3 a cross-sectional view of the power module according to the first embodiment;
• 4 a plan view of a second embodiment of the power module according to the invention;
• 5 Plots of gate-source voltage, drain-source voltage and drain-source current versus time and gate-source voltage versus frequency for a power module without shielding structure;
• 6 Plots of gate-source voltage, drain-source voltage and drain-source current versus time and gate-source voltage versus frequency for a power module with a manganese-zinc ferrite shielding structure;
• 7 Diagrams of a gate-source voltage, a drain-source voltage and a drain-source current over time and of the gate-source voltage over frequency for a power module according to the invention with a shielding structure made of a soft ferromagnetic nickel-iron alloy;
• 8th Diagrams of a gate-source voltage, a drain-source voltage and a drain-source current over time and the gate-source voltage over frequency for a power module according to the invention with a shielding structure made of electrical steel;
• 9 a block diagram of an embodiment of an electrical power converter according to the invention; and
• 10 a schematic drawing of an electric vehicle with an embodiment of an electric drive according to the invention.

Detailed description

1 is a partial plan view of a first embodiment of a power module 1.

The power module 1 comprises a first arrangement 2 of several, here eight, dies 2a to 2h, each of which forms a transistor with a switching path. Each die 2a to 2h has a first terminal 3 (see 3 ), a second terminal 4 and a control terminal 5. The switching path is formed between the first terminal 3 and the second terminal 4 and can be switched depending on a voltage at the control terminal 5 and the second terminal 4. In the present embodiment, the transistor is implemented as an example as a SiC-MOSFET with a maximum blocking voltage of 1200 V. Thus, the first terminal 3 is a drain terminal, the second terminal 4 is a source terminal and the control terminal is a gate terminal. Furthermore, in 1 an optional Kelvin connector 6 is shown.

The transistors are connected in parallel by connecting the first terminals 3 and the second terminals 4. In the 1 In the exemplary configuration shown, the second terminals 4 are connected to an electrically conductive first pad 8 by electrical connections 7a, and the first terminals 3 are connected by mounting on electrically conductive second pads 9 and by electrical connections 7b between the second pads 9. Furthermore, the control terminals 5 are connected to an electrically conductive track 11 via electrical connections 7c, thereby forming a common control signal supply for the dies 2a to 2h. The conductor track 11 extends, for example, between the second pads 9, and the electrical connections 7b jump over the conductor track 11. The optional Kelvin terminal is connected to a third pad 12 via electrical connections 7d. The aforementioned electrical connections 7a to 7d can be formed by wire connections.

2 and 3 show the first arrangement 2, where 2 a top view and 3 is a cross-sectional view.

The first arrangement 2 further comprises a plate-shaped shielding structure 13 which completely covers the dies 2a to 2h. The shielding structure 13 consists of a nickel-zinc-based ferrite, a soft ferromagnetic nickel-iron alloy or an electrical steel or of a combination of two or three of these materials. In the case of the nickel-zinc-based ferrite, a maximum of the imaginary part of its complex permeability lies between 10 MHz and 1 GHz, and at a frequency of 100 MHz, preferably 50 MHz, particularly preferably 10 MHz, the real part of the complex permeability is reduced by a factor of two or even ten compared to its value for frequencies approaching zero.

In the present embodiment, the power module 1 further comprises a carrier 14 and the arrangement 2 further comprises a support structure 15. The carrier 14 is made of ceramic and forms a DBC (directly bonded copper substrate) or an AMB (soldered active metal substrate) structure, wherein the pads 8, 9 and the conductor track 11 are made of copper, or it forms a directly bonded aluminum substrate (DBA), wherein the pads 8, 9 and the conductor track 11 are made of aluminum. The dies 2a to 2h are arranged between the carrier 14 and the shielding structure 13. The support structure 15 is electrically insulating and supports the shielding structure 13 at a predefined distance from the dies 2a to 2h. For this purpose, the support structure 15 is a frame on which the shielding structure is arranged.

Furthermore, the power module 1 comprises a single body 16 which is formed from electrically insulating molding material. The body 16 covers the dies 2a to 2h, the electrical connections 7a to 7d, the pads 8, 9, 12 and the conductor track 11. The shielding structure 13 and the support structure 15 are also embedded in the body 16.

According to 1 the power module 1 comprises a second arrangement 2', which corresponds to the first arrangement 2. The first terminals 3 of the first arrangement 2 are connected via further electrical connections 7e to the second terminals 4 of the second arrangement 2' such that they form a half-bridge.

4 is a detailed plan view of the first arrangement 2 according to a second embodiment of a power module 1. The second embodiment corresponds to the first embodiment, the differences being discussed below. Identical or equivalent components are designated by the same reference numerals.

Compared to the first embodiment, the conductor track 11 extends between the first pad 8 and the second pad 9, and the shielding structure 13 only covers the dies 2a, 2b, 2c, 2e, 2f, 2g. That is, the shielding structure 13 does not cover the dies 2d, 2h with the smallest distance to the first pad 8.

In this embodiment, the shielding structure 13 may be smaller than in the first embodiment, since feedback loops formed between the first terminals 3 of the dies 2d, 2h and the first pad 8 are substantially smaller than the corresponding feedback loops between the first terminals 3 of the other dies 2a, 2b, 2c, 2e, 2f, 2g and the first pad 8. On the other hand, it is possible not to cover the dies 2d, 2h, since feedback loops formed between the conductive line 11 and the first pad 8 are substantially smaller than the corresponding feedback loops across the other dies 2a, 2b, 2c, 2e, 2f, 2g. It should be noted that effects of the feedback loops between the first terminals 3 and the first pad 8 on the one hand and the effects of the feedback loops via the conductor track 11 and the third pad 12 on the other hand should be evaluated in detail in order to decide which of the dies 2a to 2h are not covered by the shielding structure 13.

According to another embodiment, the carrier 14 is made of a metal with a dielectric coating (not shown) thereon, thereby forming an insulated metal substrate (IMS).

According to a further embodiment, a carrier is omitted and the body 16 covers or embeds the dies 2a to 2h, the electrical connections 7a to 7d, the pads 8, 9, 12 and the conductor track 11, so that a TML (transfer molded lead frame) design is created.

According to a further embodiment, the support structure 15 is a plurality of domes, each of which selectively supports the shielding structure 13. In addition, the support structure 15 can be electrically connected to the shielding structure 13.

5 until 8th show diagrams of a gate-source voltage u _GS , a drain-source voltage u _DS and a drain-source current i _DS over time t and the spectral decomposition of the gate-source voltage u _GS over frequency f. Note that in each right-hand diagram the gate-source voltage u _GS is normalized by a factor x. All signals were measured at the external pads or auxiliary terminals of the power module 1.

5 refers to a power module corresponding to the power module 1 according to the first embodiment without a shielding structure. As can be seen, a switching signal causing the power module to turn off causes significant oscillations of the gate-source voltage due to inductive feedback loops formed by the parallel connection of the dies 2a to 2h in combination with nonlinear voltage-dependent capacitances of the transistors. It can be observed that the oscillations have a peak at 198 MHz with a normalized magnitude a = 1.

und ein Maximum des Imaginärteils der komplexen Permeabilität ${\mu }_r^{"}$

bei einer sehr niedrigen Frequenz von etwa 2 MHz aufweist. Daher wird ein Ferrit auf Nickel-Zink-Basis mit z.B. ${\mu }_r^{\text{'}}=\mathrm{2..3}$

bei der Spitzenfrequenz und einem Maximum von ${\mu }_r^{"}$

bei 70...100 MHz, das wesentlich näher an der Spitzenfrequenz liegt, als Material der Abschirmstruktur 13 gemäß den Ausführungsformen vorgeschlagen. 6 refers to a power module corresponding to power module 1 according to the first design with a shielding structure made of a manganese-zinc ferrite. Such a shielding structure even amplifies the oscillations to a normalized value a = 2.26 with a slight shift of the peak to 196 MHz. This negative effect is caused by the fact that the real part of the complex permeability of such a ferrite in the peak has a relatively high value ${\mu }_r^{\text{'}}$

and a maximum of the imaginary part of the complex permeability ${\mu }_r^{"}$

at a very low frequency of about 2 MHz. Therefore, a nickel-zinc-based ferrite with e.g. ${\mu }_r^{\text{'}}=\mathrm{2..3}$

at the peak frequency and a maximum of ${\mu }_r^{"}$

at 70...100 MHz, which is much closer to the peak frequency, is proposed as the material of the shielding structure 13 according to the embodiments.

7 refers to the first embodiment, wherein the shielding structure 13 is made of a soft ferromagnetic nickel-iron alloy such as permalloy or mu-metal. As can be seen, the oscillation is damped to a normalized magnitude a = 0.47 with a shift of the peak to 200 MHz, although such an alloy would not normally be expected to have pronounced high frequency properties in the VHF range.

8th refers to the first embodiment, wherein the shielding structure 13 is made of electrical steel. The electrical steel is M330-35 according to the standard EN 10106:2015. As can be seen, the oscillation is damped to a normalized magnitude a = 0.14 with a shift of the peak to 208 MHz, although such electrical steel is normally expected not to have pronounced high frequency properties in the VHF range.

9 is a block diagram of one embodiment of an electrical power converter 100.

The electrical power converter 100 forms an inverter and comprises a DC connection 101 with two lines 102a, 102b for a direct voltage, an AC connection 103 with several phase conductors 104u, 104v, 104w for an alternating voltage and a power section 105.

The power section 105 comprises a plurality of switching elements. The switching elements are connected to form a half-bridge 106u, 106v, 106w for each phase conductor 104u, 104v, 104w. Each half-bridge 106u, 106v, 106w is formed by a power module 1 according to one of the above embodiments, so that each switching element is formed by one of the arrangements 2, 2'. Furthermore, each half-bridge 106u, 106v, 106 is connected to the direct voltage 101, and each phase conductor 106u, 106v, 106w is connected to a central tap 107u, 107v, 107w between the switching elements of one of the half-bridges 106u, 106v, 106w. The connections between the switching elements are realized by the electrical connectors 7e (see 1 ).

10 is a schematic drawing of an electric vehicle 110 with an embodiment of an electric drive 111.

The electric drive 111 includes an electric machine 112 configured to drive the vehicle 110 and an electric power converter 100 according to the above embodiment. The electric machine 112 is connected to the AC connection 103 for supplying the electric machine 112. Furthermore, the DC connection 101 is connected to a high-voltage battery 113 of the vehicle 110.

The electric vehicle 110 comprises wheels 114 that are coupled directly or indirectly, e.g. via a transmission, to the electric drive 111 in order to rotate the wheels 114. According to the embodiment, the electric vehicle 110 is a battery electric vehicle (BEV). Alternatively, the electric vehicle 110 can additionally comprise an internal combustion engine, thereby creating a hybrid vehicle. Furthermore, the electric vehicle 110 can comprise a fuel cell that supplies the electrical power converter 100.

QUOTES INCLUDED IN THE DESCRIPTION

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

Cited patent literature

• DE 102019202728 A1 [0006]
• US 20030011057 A1 [0007]

Cited non-patent literature

• I. Kovacevic-Badstübner, U. Grossner, D. Popescu and B. Popescu, “Transient Stability Analysis of Discrete and Multi-chip Power Semiconductor Packages”, 2021 33 ^rd International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2021, pp. 391-394 [0003]
• I. Kasko, SE Berberich, M. Spang and S. Oehling, “SiC MOS Power Module in Direct Pressed Die Technology and some Challenges for Implementation”, 2020 32 ^nd International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2020, pp. 364-367 [0005]

Claims (15)

Power module (1) comprising at least one arrangement (2, 2') of a plurality of dies (2a-h), each of which forms a transistor with a switching path, each die (2a-h) having a first terminal (3), a second terminal (4) and a control terminal (5), the switching path being formed between the first terminal (3) and the second terminal (4) and being switchable as a function of a voltage at the control terminal (5) and the second terminal (4), the transistors being connected in parallel by the first terminals (3) being connected to one another and the second terminals (4) being connected to one another, characterized in that the at least one arrangement (2, 2') comprises a shielding structure (13) which at least partially covers at least two of the dies (2a-h), the shielding structure (13) comprising or consisting of one or more materials selected from a group consisting of a nickel-zinc-based ferrite, a soft ferromagnetic nickel-iron alloy and a Electric steel. Power module according to Claim 1 , wherein electrical connections (7a-d) between the dies (2a-h) form an oscillating circuit with one or more resonant frequencies of at least 100 MHz and feedback loops which form an inductive coupling between the second terminals (4) on the one hand and the first terminals (3) and/or control terminals (5) on the other hand, wherein the shielding structure (13) is configured to reduce the inductive coupling. Power module according to Claim 1 or 2 , wherein the nickel-zinc-based ferrite has a complex permeability with a real part and an imaginary part, wherein - within a frequency range between 10 MHz and 1 GHz there is a maximum of the imaginary part and/or - at a frequency of 100 MHz, preferably 50 MHz, particularly preferably 10 MHz, the real part of the complex permeability is reduced compared to its value at frequencies close to zero. Power module according to one of the preceding claims, wherein the shielding structure (13) is plate-shaped. Power module according to one of the preceding claims, wherein the at least one arrangement (2, 2') further comprises an electrically conductive pad (8) to which the second terminals (4) are connected, and - an electrically conductive second pad (9) to which the first terminals (3) are connected, wherein the shielding structure (13) does not cover the die (2d) with the smallest distance to the first pad (8), and/or - an electrically conductive track (13) to which the control terminals (5) are connected, wherein the shielding structure (13) does not cover the die (2a) with the smallest distance to the first pad (8) or to an electrically conductive further pad (12) of the power module (1), wherein Kelvin terminals (6) of the dies (2a-h) are connected to the further pad (12). Power module according to one of the Claims 1 until 4 , wherein the shielding structure (13) at least partially covers each die (2a-h). Power module according to one of the preceding claims, wherein the shielding structure (13) completely covers the at least two dies (2a-h). Power module according to one of the preceding claims, further comprising a single body (16) of electrically insulating molding material, wherein the body (16) covers the dies (2a-h) and/or electrical connections (7a-d) between the dies, wherein the body (16) embeds the shielding structure (13). Power module according to one of the preceding claims, further comprising a carrier (14) on which the dies (2a-h) are mounted, wherein the at least two dies (2a-h) are arranged between the carrier (14) and the shielding structure (13). Power module according to one of the preceding claims, wherein the at least one arrangement (2, 2') further comprises a support structure (15) which supports the shielding structure (13). Power module according to the Claims 9 and 10 , wherein the support structure (15) is mounted on the carrier (14). Power module according to Claim 10 or 11 , wherein the support structure (15) - is electrically insulating and/or - is a frame on which the shielding structure (13) is arranged, or a plurality of domes, each of which selectively supports the shielding structure (13). Power module according to one of the preceding claims, wherein a first arrangement (2) and a second arrangement (2') are present, wherein the first terminals (3) of the first arrangement (2) are connected to the second terminals (4) of the second arrangement (2') so as to form a half-bridge (106u, 106v, 106w). Electrical power converter (100), comprising - a DC connection (101) for a direct voltage; - an AC connection (103) with a plurality of phase conductors (104u, 104v, 104w) for an alternating voltage; and - a power section (105) comprising a plurality of switching elements connected together to form a half-bridge (106u, 106v, 106w) for each phase conductor, each half-bridge (106u, 106v, 106w) being connected to the DC connection (101) and each phase conductor (104u, 104v, 104w) being connected to a central tap (107u, 107v, 107w) between the switching elements of one of the half-bridges (106u, 106v, 106w); wherein each switching element or each half-bridge (106u, 106v, 106w) is formed by a power module (1) according to one of the preceding claims. Electric drive (111) for a means of transport, for example for a vehicle (110) or for a bicycle, comprising an electric machine (112) configured to drive the means of transport (110) and an electric power converter (100) according to Claim 14 , wherein the electrical machine (112) is connected to the AC connection (103) of the electrical power converter (100) for supplying the electrical machine (112) with the alternating voltage.

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