Multilevel converter with optimized topology

Abstract

The present invention relates to a multilevel converter having an optimized topology, and more particularly to an electric power circuit having a substrate and a first circuit board, each having an upper side and a lower side. The lower side of the substrate is connected to a cooling body. A first electrical switching element is arranged on the upper side of the substrate, by means of which the alternating current potential present at the phase terminal can be connected to the high direct current potential present at the first potential terminal and to the low direct current potential present at the second potential terminal. By means of a second electrical switching element, the alternating current potential can be connected to the medium direct current potential present at the third potential terminal. The substrate is arranged at a distance from the first circuit board below the lower side of the first circuit board such that the upper side of the substrate faces the first circuit board. The substrate is electrically connected to the first circuit board. The second electrical switching element is arranged at least on the upper side of the first circuit board and, if possible, also at the lower side of the first circuit board.

Description

Technical Field

[0001] The present invention relates to an electric power circuit,

[0002] wherein the electric power circuit has a substrate with an upper side and a lower side,

[0003] wherein the lower side of the substrate is connected to a cooling body,

[0004] wherein a first electric switch element is arranged on the upper side of the substrate, and by means of the first electric switch element, the alternating current potential present at the phase terminal of the electric power circuit can be connected to the high direct current potential present at the first potential terminal of the electric power circuit and to the low direct current potential present at the second potential terminal of the electric power circuit,

[0005] wherein the electric power circuit has a second electric switch element, and by means of the second electric switch element, the alternating current potential present at the phase terminal can be connected to the medium direct current potential present at the third potential terminal of the electric power circuit,

[0006] wherein, in addition to the substrate, the electric power circuit further has a first circuit board with an upper side and a lower side,

[0007] wherein the substrate is arranged below the lower side of the first circuit board at a distance from the first circuit board, such that the upper side of the substrate faces the first circuit board,

[0008] wherein the substrate is electrically connected to the first circuit board. Background Art

[0009] Such electric power circuits are generally known. In particular, so-called 3L converters (3L = 3 levels = 3 different voltage levels on the DC voltage side) are designed in this way. The medium DC potential is, as its name implies, between the high DC potential and the low DC potential. The medium DC potential is mainly in the middle or at least approximately in the middle between the high DC potential and the low DC potential.

[0010] A power module unit is known from WO 2020 / 052 829 A1, which has a substrate with an upper side and a lower side. Power semiconductors are arranged on the upper side of the substrate. The lower side of the substrate is connected to a cooling body.

[0011] The published document DE 10 2015 224 431 A1 describes a semiconductor component, which includes a plurality of semiconductor units respectively forming a three-point inverter circuit and a connection unit for paralleling the semiconductor units. Each of the semiconductor units includes a multilayer substrate including an insulating board and a circuit board arranged on the primary surface of the insulating board, a plurality of semiconductor elements respectively having a back surface fastened to one of the circuit boards and a front surface with a primary electrode, and a wiring element electrically connected to the primary electrode of the semiconductor element. And in each of the semiconductor units, the multilayer substrate, the plurality of semiconductor elements and the wiring element are configured to form a three-point inverter circuit.

[0012] The published document US 2020 / 0204082 A1 describes a power conversion device, which includes first to fourth switching elements and first to eighth diodes. The first to fourth diodes are electrically connected to the first to fourth switching elements in an anti-parallel manner. The seventh diode is electrically parallel to the second diode. The eighth diode is electrically parallel to the third diode. The second diode is arranged in the first housing. The seventh diode is arranged in the second housing, which is different from the first housing and does not include a switching element. The eighth diode is arranged in the second housing, or alternatively, the eighth diode is arranged in another housing, which is different from the first housing and the second housing and does not include a switching element.

[0013] Recently, the following electronic semiconductors have become increasingly well-known, which are also called so-called WBG components. "WBG" is an abbreviation for "wide band gap" in this case. Typical representatives of such semiconductor switches are switching elements based on silicon carbide (SiC) and gallium nitride (GaN). New silicon (Si)-based switching elements can also be so called. The switching element can be, for example, a thyristor, an IGBT, and an FET (including MOSFET and JFET).

[0014] The gallium nitride-based switching element has many technical advantages. In particular, it has a particularly short switching time, that is, it can transition from the off state (=non-conductive) to the on state (=conductive) in a very short time, or vice versa from the on state to the off state. The switching time can be in the range of several ns and even less than 1 ns. However, the gallium nitride-based switching element also has disadvantages in practical applications. That is, such a switching element is only suitable for short circuits with a significantly shorter duration than other switching elements, for example. In addition, it can usually only be in a housing and cannot be a housingless switching element (die). Thus, the losses accumulated in the corresponding gallium nitride-based switching element can only be dissipated relatively poorly. Finally, the maximum switching voltage limited by the structure in the gallium nitride-based switching element is limited to a range significantly lower than 1 kV. It is currently limited to about 650 V in practice.

[0015] Compared with gallium nitride-based switching elements, silicon carbide-based switching elements are capable of handling short circuits of significantly longer durations. They can be installed in a housing and as a housingless switching element (die). Their structure can be offered on the market, in which the maximum switching voltage defined by the construction is in the range of multiple kV, for example up to 3 kV.

[0016] Therefore, in practice, converters, switching power supplies, and analogues for switching high voltages and high powers still use silicon carbide-based switching elements despite the advantages of gallium nitride-based switching elements, because they can be arranged on a substrate without major problems and cooled well there. In lower voltages and / or lower powers, gallium nitride-based switching elements are also partly used in the prior art. However, these switching elements are arranged on a conventionally designed circuit board in this case. Summary of the Invention

[0017] The object of the present invention is to improve an electric power circuit of the type described at the beginning, so that it is designed in a simple, low-cost, and technically advantageous manner and method.

[0018] This object is achieved by the electric power circuit of the present invention.

[0019] According to the present invention, an electric power circuit of the type described at the beginning is designed such that

[0020] at least a second electrical switching element is arranged on the upper side of the first circuit board, and additionally on the lower side of the first circuit board if possible.

[0021] Since the arrangement of the first electrical switching element on the substrate can (as in the prior art) connect high voltages and high powers, and thus good dissipation of the loss power accumulated in the first electrical switching element can be achieved via a cooling body. By arranging the second electrical switching element on the first circuit board, the circuit can be realized more simply. In particular, the second electrical switching element does not have to be arranged on the substrate so that the loss power to be dissipated via the cooling body is less than when the second electrical switching element is also arranged on the substrate as an addition to the first electrical switching element (as is usually the case in the prior art). In addition, more space is provided for the placement of the first and second electrical switching elements, i.e., the area of the substrate together with the area of the circuit board.

[0022] Preferably, the first electrical switching element has a greater loss power than the second electrical switching element during the operation of the electric power circuit. Thereby, the arrangement of the second electrical switching element does not cause major problems when dissipating the loss power accumulated during the operation of the second electrical switching element.

[0023] The alternating potential varies between an upper value and a lower value as a function of time. The upper value and the lower value are mainly in the range of a high DC potential and a low DC potential. The lower power loss of the second electrical switching element can be fully derived from itself due to the average of the smaller connected potential difference. However, it can also be due to other reasons. The reasons for the mutually different power losses can particularly lie in that, compared to the second electrical switching element, the first electrical switching element has a higher conduction voltage and / or more switching times and / or a higher conduction resistance.

[0024] The conduction voltage is the voltage that drops across the respective electrical switching element in the on-state of the respective electrical switching element. The conduction voltage, in combination with the connected current, results in the power loss accumulated in the respective electrical switching element (Power = Voltage × Current). The turn-on time is the time required to switch the respective electrical switching element from the off-state to the on-state or vice versa. During the switching, the respective electrical switching element is in a transient state, in which on the one hand a relatively large voltage (significantly greater than the conduction voltage) drops across the respective electrical switching element, and on the other hand the rated current already flows. The transient state is only allowed to be maintained for a short time. The longer the transient state lasts, the greater the switching time and the greater the switching energy, which accumulates in the respective electrical switching element during each switching process and must be dissipated as heat.

[0025] In particular, the reasons for the mutually different conduction voltages and / or mutually different switching times can lie in that the first electrical switching element and the second electrical switching element are implemented in different semiconductor technologies. In particular, the first electrical switching element can be configured as a silicon carbide-based switching element, and the second electrical switching element can be configured as a gallium nitride-based switching element.

[0026] Preferably, the first electrical switching element is configured as a housingless switching element. Such a switching element is called a die element in the art. Due to the application of the housingless switching element, the power loss accumulated in the first electrical switching element can be quickly transferred to the substrate and then further to the cooling body from there.

[0027] In contrast, the second electrical power circuit element is preferably configured as a switching element arranged in a housing, wherein the second electrical switching element is also fastened to the first circuit board by means of the housing. In particular, the second electrical switching element can be applied in this way in the case of using a gallium nitride-based switching element, as it is usually provided. Usually, the second electrical switching element is soldered to the first circuit board. However, the second electrical switching element can also be fixed to the first circuit board by clamping.

[0028] Each electrical switching element has a maximum switching voltage defined by its construction. The maximum switching voltage is the voltage at which the respective electrical switching element can still allow or remain in the cut-off state. In this regard, the risk that occurs when the voltage is higher than the maximum switching voltage is that the switching from the on state to the off state can no longer be achieved and / or directly causes electrical breakdown of the electrical switching element, making the electrical switching element permanently conductive. Preferably, the maximum switching voltage defined by the construction of the first electrical switching element is greater than the maximum switching voltage defined by the construction of the second electrical switching element. Generally, the quotient of these voltages is between 1.2 and 2.0. Therefore, the maximum switching voltage defined by the construction of the first electrical switching element is generally 20% to 100% greater than the maximum switching voltage defined by the construction of the second electrical switching element. Particularly preferably, the maximum switching voltage defined by the construction of the first electrical switching element can be higher than the voltage of a gallium nitride-based switching element, while the maximum switching voltage defined by the construction of the second electrical switching element is lower than this voltage.

[0029] The first current paths are electrically connected to each other by turning on the first electrical switching element. The first current paths are electrically isolated from each other by turning off the first electrical switching element. Therefore, the first current paths are switched by means of the first electrical switching element. Preferably, the first electrical switching element is bridged by a first auxiliary circuit including a first capacitor. Thereby, an improved current profile is obtained. Preferably, the first auxiliary circuit is arranged on the substrate. Thereby, the first auxiliary circuit can act particularly effectively.

[0030] In a similar manner, the second current paths are conductively connected to each other and electrically isolated from each other, i.e., switched, by turning on and off the second electrical switching element. Preferably, the second electrical switching element is bridged by a second auxiliary circuit including a second capacitor. Thereby, an improved current profile (as before) is obtained. Preferably, the second auxiliary circuit is arranged on the first circuit board. Thereby, the second auxiliary circuit can act particularly effectively.

[0031] The first and second capacitors of the auxiliary circuit are known in the art as pulse capacitors. They are generally constructed as ceramic capacitors.

[0032] Preferably, a cooling element is arranged at the lower side of the first circuit board, and the loss power accumulated in the second electrical switching element is dissipated by means of the cooling element. Thereby, it is not serious when relatively more loss power accumulates in the second electrical switching element.

[0033] The cooling element extends away from the first circuit board only so that the cooling element is also spaced apart from the substrate. The cooling element can also be regarded as a cooling body. The choice of the term "cooling element" (compared with "cooling body") is basically used to linguistically distinguish it from the cooling body of the substrate.

[0034] Preferably, at least one second circuit board electrically connected to the first circuit board and / or the substrate is arranged between the first circuit board and the substrate. Thereby, greater freedom is obtained when arranging various electronic components (switching elements and other components) and an improved utilization rate of the volume required for the electric power circuit is achieved.

[0035] Preferably, the lower side surface of the substrate is directly connected to the cooling body via a heat-conducting paste or via a metal layer. Thereby, the losses accumulated in the first electrical switching element can be discharged particularly well to the cooling body.

[0036] The electric power circuit according to the invention is generally used in a converter. The converter can be, for example, a rectifier, an inverter, a converter or a DC voltage converter. Alternatively, the electric power circuit according to the invention can be applied in a switching power supply. Description of the Drawings

[0037] The above characteristics, features and advantages of the present invention and the ways and means of implementation are clearly and clearly explained in connection with the description of the embodiments detailed below with reference to the accompanying drawings. It is schematically shown here:

[0038] Figure 1 A circuit block diagram showing the electric power circuit,

[0039] Figure 2 A time chart is shown,

[0040] Figure 3 Shows Figure 1 The mechanical design structure of the electric power circuit,

[0041] Figure 4 The substrate and the cooling body are shown,

[0042] Figure 5 The substrate and the cooling body are shown,

[0043] Figure 6 A time chart is shown, and

[0044] Figure 7 An I-V characteristic curve is shown,

[0045] Figure 8 Shows Figure 1 A variant of the circuit block diagram, and

[0046] Figure 9 Shows Figure 3 A variant of the mechanical design structure. Detailed Description of the Preferred Embodiments

[0047] Figure 1 The electric power circuit 1 and a downstream load in the form of an inverter (DC / AC) and a motor (M) are shown. The downstream load is not part of the present invention.

[0048] The electric power circuit 1 has a first electric switching element 2. The first electric switching element 2 can be configured, for example, as a thyristor, an IGBT (insulated gate bipolar transistor), or according to Figure 1 configured as a FET (Feldeffekttransistoren, field effect transistor). A special case of the FET is the MOSFET. The first electric switching element 2 according to Figure 1 is usually connected in parallel with a diode. The diode can be an independent component or an inherent part of the first electric switching element 2.

[0049] The first electric switching element 2 can be alternately switched on or off. The corresponding switching state is determined by the control signals S1, S2 supplied to the first electric switching element 2. The control signals S1, S2 are generated by the control device 3.

[0050] By means of one of the two first electric switching elements 2, the alternating potential U~ can be connected to the high DC potential U+. By means of the other of the two first electric switching elements 2, the alternating potential U~ can be connected to the low DC potential U-. The alternating potential U~ is present at the phase terminal 4 of the power supply circuit 1, the high DC potential U+ is present at the first potential terminal 5 of the power supply circuit 1, and the low DC potential U- is present at the second potential terminal 6 of the power supply circuit 1.

[0051] The electric power circuit 1 further has a second electric switching element 7. Usually, there are two second electric switching elements 7, which according to Figure 1 are connected in series with each other. The second electric switching element 7 can be configured, for example, as a thyristor, an IGBT or a FET similar to the first electric switching element 2. The second electric switching element according to Figure 1 is usually also connected in parallel with a diode. The diode can be an independent component or an inherent part of the second electric switching element 7, similar to the diode connected in parallel with the first electric switching element 2.

[0052] The two second electric switching elements 7 can be alternately switched on or off. The corresponding switching state is determined by the control signals S3, S4 supplied to the second electric switching element 7. The control signals S3, S4 are generated by the control device 3. In many cases, the same drive of the two second electric switching elements 7 can be achieved, that is, both of the two second electric switching elements 7 are switched on or both are switched off.

[0053] By means of the second electric switching element 7, the alternating potential U~ can be connected to the medium DC potential U0. The medium DC potential U0 is present at the third potential terminal 8 of the power supply circuit 1. The medium DC potential is between the high DC potential U+ and the low DC potential U-, mainly (at least approximately) in the middle between the high DC potential U+ and the low DC potential U-.

[0054] Generally according to Figure 1 There is a capacitor 9 via which the third potential terminal 8 is capacitively coupled to the first and second potential terminals 4, 5. In particular, it is thereby achieved that the medium DC potential U0 is between the high DC potential U+ and the low DC potential U-.

[0055] The first electrical switching element 2 and the second electrical switching element 7 are each controlled such that the AC potential U~ is connected to one of the DC potentials U+, U-, U0 at each point in time. However, short - time exceptions can occur exceptionally during the instantaneous states of the first electrical switching element 2 and the second electrical switching element 7. The AC potential U~ is connected to only one of the DC potentials U+, U-, U0 respectively in Figure 2 is shown in Figure 2 is shown as a function of time t which DC potential U+, U-, U0 the AC potential U~ is connected to respectively. It is shown that the time periods during which the AC potential U~ is connected to one of the three DC potentials U+, U-, U0 are separated from each other by small gaps.

[0056] A resistor R can be arranged between the phase terminal 4 and the first electrical switching element 2 and the second electrical switching element 7 according to Figure 1 The resistor R is a shunt resistor which is used to detect and regulate the actually connected current on this basis. A resistor R can be arranged between the phase terminal 4 and the first electrical switching element 2 and the second electrical switching element 7 according to Figure 1 An inductor L can also be arranged. The inductor L is used for rectification. The resistor R, if present, is a component of the electrical power circuit 1. The inductor L can be a component of the electrical power circuit 1. Alternatively, the inductor can not be a component of the electrical power circuit 1 but an independent component.

[0057] The above - mentioned combination Figure 1 and Figure 2 The electrical power circuit 1 described is generally known. In particular, it can be applied in converters or switching power supplies.

[0058] To implement the electrical power circuit 1 described above in combination Figure 1 The electrical power circuit 1 has a substrate 10 and a first circuit board 11 according to the view of Figure 3

[0059] The substrate 10 has an upper side and a lower side. Corresponding metal layers are coated on the upper side and the lower side. The metal layers can be structured. The substrate 10 itself consists of an insulating material which (at least generally) has a thickness between 25 μm and 400 μm. In particular, the insulating material can be made of a ceramic material, such as aluminum nitride or alumina. Alternatively, it can be made of a plastic, such as polyamide or polyimide.

[0060] ​On the upper side of the substrate 10, a first electrical switching element 2 is arranged. In particular, the first electrical switching element 2 can be arranged on the substrate 10 in a material - fitting manner. Suitable material - fitting connections are, for example, welding or sintering connections. The connection of the first electrical switching element 2 to the substrate 10 is generally referred to as DCB (direct copper bonding) or DBC (direct bonding copper). Preferably, the resistor R (not shown in Figure 3 is also arranged on the upper side of the substrate 10 as long as it exists. However, the resistor R can also be arranged at other positions, for example, on the first circuit board 11.

[0061] The lower side of the substrate 10 is connected to the cooling body 12. The cooling body 12 is made of a metal with good thermal conductivity, which is typically aluminum or an aluminum alloy, and sometimes also copper or a copper alloy. In each case, the cooling body 12 has Figure 3 cooling ribs. The power loss accumulated in the first electrical switching element 2 or elsewhere can be conducted from the substrate 10 into the cooling body 12 and sent from the cooling body 12 into the surrounding environment.

[0062] In order to thermally couple the substrate 10 to the cooling body 12, it can be achieved that the lower side of the substrate 10 is Figure 3 directly connected to the cooling body 12. Alternatively, it can be achieved that the lower side of the substrate 10 is connected to the cooling body 12 via a thermal paste 13. Another alternative is that the lower side of the substrate 10 is Figure 4 connected to the cooling body 12 via a metal layer 14. Figure 5

[0063] The first circuit board 11 is generally constructed as a conventional circuit board, that is, made of glass fiber mats impregnated with resin or glass fiber fabrics impregnated with resin. A typical example is the so - called FR4 circuit board. Alternatively, the circuit board can also be made of polyimide (with or without glass fibers) or PTFE (with or without glass fibers). In individual cases, the circuit board 11 can also be made of ceramics, especially alumina.

[0064] The first circuit board 11 also has Figure 3 an upper side and a lower side. The second electrical switching element 7 is arranged at least on the upper side of the first circuit board 11. If possible, the second electrical switching element 7 is Figure 3 partially arranged on the upper side of the first circuit board 11 and partially on the lower side.

[0065] The substrate 10 is arranged below the lower side of the first circuit board 11 at a spacing a from the first circuit board 11. The spacing a is generally in the range of several centimeters. The upper side of the substrate 10 faces the first circuit board 11.

[0066] The substrate 10 is electrically connected to the first circuit board 11. The corresponding electrical connection V is first used to conduct the voltage and current connected by means of the first electrical switching element 2. The control device 3 is usually arranged on the first circuit board 11. In this case, the electrical connection V is also used to transmit the control signals S1 and S2 to the first electrical switching element 2.

[0067] Due to the arrangement of the first electrical switching element 2 on the substrate 10, it is possible that the first electrical switching element 2 operates with a relatively high power loss. However, due to the arrangement of the second electrical switching element 7 on the first circuit board 11, the second electrical switching element 7 can only operate with a relatively small power loss. This usually follows completely from the mode of operation itself. Because when the amplitude of the alternating potential U~ is marked with A, in the most unfavorable case, it may be required that two first electrical switching elements 2 conduct the voltage, which has the potential U+ and the value A. For the first electrical switching element 2, this occurs when the alternating potential U~ currently has the value -A and the alternating potential U~ is connected to the high DC potential U+. For the other first electrical switching element 2, this occurs when the alternating potential U~ currently has the value +A and the alternating potential U~ is connected to the low DC potential U-. In contrast, the medium DC potential U0 is usually in the zero-crossing range of the alternating potential U~. Therefore, when connected to the medium DC potential U0, it is necessary to conduct basically only the voltage with the value A even in the most unfavorable case.

[0068] However, there can be other reasons for this. Due to this, the first electrical switching element 2 has a greater power loss than the second electrical switching element 7 during the operation of the electrical power circuit 1. For example, according to Figure 6 It is possible that the first electrical switching element 2 requires a switching time T1 to switch from the off state to the on state and a switching time T1' to switch from the on state to the off state, while the second electrical switching element 7 requires a switching time T2 to switch from the off state to the on state and a switching time T2' to switch from the on state to the off state, where the switching times T2, T2' are less than the switching times T1, T1'. The ratio of the switching times T1, T1' or T2, T2' can be, for example, between 3 and 20. Another possible reason for the difference in power loss can lie in the fact that, according to Figure 7 When conducting the current I, the conduction voltage U1 drops across the first electrical switching element 2 and the conduction voltage U2 drops across the second electrical switching element 7, where the conduction voltage U2 of the second electrical switching element 7 is less than the conduction voltage U1 of the first electrical switching element 2. In a similar manner, it is also possible that the first electrical switching element 2 has a greater on-resistance than the second electrical switching element 7 in the on state. In particular, the latter case can occur in single-stage switching elements, especially FETs.

[0069] In order to particularly well implement guiding the power loss occurring in the first electrical switching element 2 into the substrate 10 and further from there to the cooling body 12, the first electrical switching element 2 is preferably configured as a housingless switching element (die). In particular, it is shown in Figures 3 to 5 as the first electrical switching element 2 drawn very flatly. In contrast, the second electrical switching element 7 is generally configured as a switching element arranged in a housing. In this case, the second electrical switching element 7 is (apparently) fixed to the first circuit board 11 by means of the housing, for example, soldered and fixed there. The switching element configured to be arranged in the housing is shown in Figure 3 as the second electrical switching element 7 drawn significantly higher and to some extent wider compared to the first electrical switching element 2.

[0070] As already mentioned, the first electrical switching element 2 must be able to switch on and also switch off a greater voltage than the second electrical switching element 7. Thus, it is achievable that the maximum switching voltage defined by the configuration of the first electrical switching element 2 is greater than the maximum switching voltage defined by the configuration of the second electrical switching element 7. This is generally also advantageous because an electrical switching element with a lower maximum switching voltage defined by the configuration is usually less costly compared to an electrical switching element with a greater maximum switching voltage defined by the configuration.

[0071] Preferably, the maximum switching voltage of the second electrical switching element 7 has a value of 650 V or less. Conversely, the maximum switching voltage of the first electrical switching element 2 can also have a greater value, for example, 1 kV or greater. However, it is obvious that other values are also possible. In particular, in the case where the maximum switching voltage of the second electrical switching element 7 is a value of 650 V or less, the second electrical switching element 7 can be designed based on gallium nitride and thus has the advantages of an electrical switching element based on gallium nitride.

[0072] Figure 8 and Figure 9 show Figure 1 and Figure 3 variants of the electrical power circuit. According to Figure 8 and Figure 9 , a first capacitor 15 is provided, and the first electrical switching element 2 is bridged by means of the first capacitor. In a similar manner, a second capacitor 16 is provided, and the second electrical switching element 7 is bridged by means of the second capacitor. Figure 8 and Figure 9 also show that the first capacitor 15 is arranged on the substrate 10, while the second capacitor 16 is arranged on the first circuit board 11. In addition, the above design also applies to Figures 1 to 7 .

[0073] The first capacitor 15 and the second capacitor 16 are the simplest design of the first auxiliary circuit and the second auxiliary circuit that bridge the first electrical switching element 2 and the second electrical switching element 7. However, the first auxiliary circuit and the second auxiliary circuit can also be configured as RC mechanisms, i.e., each having a resistor connected in series with the corresponding first capacitor 15 and second capacitor 16. An improved current process curve is obtained through the first auxiliary circuit and the second auxiliary circuit.

[0074] According to Figure 8 and Figure 9 , there are also respective second capacitors 16 (or generally respective second auxiliary circuits) for the two second electrical switching elements 7. However, alternatively, it can also be achieved that the two second electrical switching elements 7 are bridged by means of a separate second capacitor 16 (or generally a separate second auxiliary circuit).

[0075] Figure 9 Two further advantageous designs of the present invention are also shown. These two designs are described together next, but can be implemented independently of each other.

[0076] On the one hand, according to Figure 9 a cooling element 17 is arranged on the lower side of the first circuit board 11. In particular, the loss power accumulated in the second electrical switching element 7 can be dissipated by means of the cooling element 17.

[0077] On the other hand, at least one second circuit board 18 is arranged between the first circuit board 11 and the substrate 10. Feasible designs of the second circuit board 18 can apply similar implementation schemes to those of the first circuit board 11. For example, a driver can be arranged on at least one second circuit board 18. The at least one second circuit board 18 is electrically connected to the first circuit board 11 and / or the substrate 10.

[0078] The present invention has been described above in connection with the individual phase terminal 4. However, it can also be achieved that the electrical power circuit 1 has a plurality of phase terminals 4. In this case, the first electrical switching element 2 and the second electrical switching element 7 exist separately for each phase terminal 4. The potential terminals 5, 6, 8 can be used in common.

[0079] Therefore, generally speaking, the present invention relates to the following situation:

[0080] The substrate 10 and the first circuit board 11 each have an upper side and a lower side. The lower side of the substrate 10 is connected to the cooling body 12. A first electrical switching element 2 is arranged on the upper side of the substrate 10. By means of the first electrical switching element, the alternating potential U~ present at the phase terminal 4 can be connected to the high direct current potential U+ present at the first potential terminal 5 and to the low direct current potential U- present at the second potential terminal 6. By means of a second electrical switching element 7, the alternating potential U~ can be connected to the medium direct current potential U0 present at the third potential terminal 8. The substrate 10 is arranged at a distance a from the first circuit board 11 below the lower side of the first circuit board 11 such that the upper side of the substrate 10 faces the first circuit board 11. The substrate 10 is electrically connected to the first circuit board 11. The second electrical switching element 7 is arranged at least on the upper side of the first circuit board 11 and, if possible, additionally at the lower side of the first circuit board 11.

[0081] The present invention has many advantages. In particular, a compact electric power circuit can be realized in a flexible manner.

[0082] Although the present invention has been elaborated and described in detail in terms of preferred embodiments, the present invention is not limited to the disclosed examples, and other variant solutions can be derived therefrom by professionals without departing from the scope of protection of the present invention.

Claims

1. An electric power circuit, wherein, the electric power circuit has a substrate (10) with an upper side and a lower side, wherein the lower side of the substrate (10) is connected to a cooling body (12), wherein a first electric switch element (2) is arranged on the upper side of the substrate (10), and by means of the first electric switch element (2), the alternating current potential (U~) present at the phase terminal (4) of the electric power circuit can be connected to the high direct current potential (U+) present at the first potential terminal (5) of the electric power circuit and to the low direct current potential (U-) present at the second potential terminal (6) of the electric power circuit, wherein the electric power circuit has a second electric switch element (7), and by means of the second electric switch element (7), the alternating current potential (U~) present at the phase terminal (4) can be connected to the medium direct current potential (U0) present at the third potential terminal (8) of the electric power circuit, wherein, in addition to the substrate (10), the electric power circuit further has a first circuit board (11) with an upper side and a lower side, wherein the substrate (10) is arranged below the lower side of the first circuit board (11) at a spacing (a) from the first circuit board (11) such that the upper side of the substrate (10) faces the first circuit board (11), wherein the substrate (10) is electrically connected to the first circuit board (11), characterized in that, the second electric switch element (7) is arranged at least on the upper side of the first circuit board (11).

2. The electric power circuit according to claim 1, characterized in that, the second electric switch element (7) is further arranged at the lower side of the first circuit board (11).

3. The electric power circuit according to claim 1 or 2, characterized in that, compared with the second electric switch element (7), the first electric switch element (2) has a greater power loss during the operation of the electric power circuit.

4. The electric power circuit according to claim 1 or 2, characterized in that, compared with the second electric switch element (7), the first electric switch element (2) has a greater conduction voltage (U1) and / or more switching times (T1, T1') and / or a greater conduction resistance.

5. The electric power circuit according to claim 1 or 2, characterized in that, the first electric switch element (2) and the second electric switch element (7) are implemented with different semiconductor technologies.

6. The electric power circuit according to claim 5, characterized in that, the first electric switch element (2) is configured as a silicon carbide-based switch element and the second electric switch element (7) is configured as a gallium nitride-based switch element.

7. The electric power circuit according to claim 1 or 2, characterized in that, the first electric switch element (2) is configured as a shell-less switch element.

8. The electric power circuit according to claim 1 or 2, characterized in that, The second electrical switching element (7) is configured as a switching element arranged in a housing, and the second electrical switching element (7) is fixed to the first circuit board (11) by means of the housing.

9. The electric power circuit according to claim 1 or 2, characterized in that the maximum switching voltage defined by the construction of the first electrical switching element (2) is greater than the maximum switching voltage defined by the construction of the second electrical switching element (7).

10. The electric power circuit according to claim 1 or 2, characterized in that the first electrical switching element (2) is bridged by means of a first auxiliary circuit comprising a first capacitor (15), and the first auxiliary circuit is arranged on the substrate (10).

11. The electric power circuit according to claim 1 or 2, characterized in that the second electrical switching element (7) is bridged by means of a second auxiliary circuit comprising a second capacitor (16), and the second auxiliary circuit is arranged on the first circuit board (11).

12. The electric power circuit according to claim 1 or 2, characterized in that a cooling element (17) is arranged at the lower side of the first circuit board (11), and the loss power accumulated in the second electrical switching element (7) is dissipated by means of the cooling element (17).

13. The electric power circuit according to claim 1 or 2, characterized in that at least one second circuit board (18) electrically connected to the first circuit board (11) and / or the substrate (10) is arranged between the first circuit board (11) and the substrate (10).

14. The electric power circuit according to claim 1 or 2, characterized in that the lower side of the substrate (10) is directly connected to the cooling body (12) via a heat-conducting paste (13) or via a metal layer (14).

15. The electric power circuit according to claim 1 or 2, characterized in that the electric power circuit is used in an inverter or in a switching power supply.

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