Power module with stabilizer circuit

Abstract

The present invention provides an electric power module with at least two semiconductor switches, e.g. SiC or GaN semiconductor switches, connected in parallel between external terminals. At least one stabilizer circuit with a resistor connected between the first and second terminals is connected to: drain connections of the both of the semiconductor switches, and / or both of the source connections of the semiconductor switches. The stabilizer circuit component(s) can be connected to internal or external terminals of the power module. The stabilizer circuit is configured to damp an electric high frequency oscillation in the power module, such as an oscillation within 1-1000 MHz. For example, the stabilizer circuit may be a resistor of 1-100 Ω which has been found to damp high frequency oscillations in power modules caused by parasitics. The stabilizer circuit has been found to provide a high frequency oscillation damping effect to ensure a stable function of the power module. Since the stabilizer circuit is connected to connecting points with zero DC voltage difference, the power loss is minimal, and further the stabilizer circuit does not influence switching characteristics of the semiconductor switches. For high safety, the power module can be arranged inside a presspack casing.

Description

[0001] 84544PC01

[0002] 1

[0003] POWER MODULE WITH STABILIZER CIRCUIT

[0004] FIELD OF THE INVENTION

[0005] The present invention relates to power electronics. Especially, the invention realtes to a power module with parallel connected semiconductor switches.

[0006] BACKGROUND OF THE INVENTION

[0007] Electric power converters implemented with wide-bandgap semiconductor material technologies such as gallium nitride (GaN) and silicon carbide (SiC) can operate at a wide range of switching frequencies, e.g. from 1 kHz to several 10s MHz.

[0008] These technologies allow high efficiency power conversion, DC-AC, AC-DC, DC-DC or AC-AC, and with several power modules combined, it is possible to reach power handling in order of 10s of kW or even 10s of MW.

[0009] However, in practical implementations wide-bandgap semiconductor based power modules have proven to introduce a number of problems with instability, and these instability problems can be detrimental to the overall function of the system and can even lead to permanent damage of the power module.

[0010] For example, a number of single-chip semiconductor devices can be combined to form a multi-chip power module thereby having a plurality of parallel connected semiconductor switches. Further, such multi-chip power modules can be combined to obtain an even higher power handling capacity.

[0011] However, in practical implementations such combined power modules often cause significant instability problems. This can be observed evn in power modules which are operated at a rather low switching frequency, e.g. at 1-10 kHz switching frequencies.

[0012] Especially, it has been observed that power modules with parallel connected semiconductor switches can suffer from instability problems that can cause permanent damage of the power modules. 84544PC01

[0013] 2

[0014] SUMMARY OF THE INVENTION

[0015] Following the above, it may be seen an object of the present invention to provide a solution to allow combination of several semiconductor switches in parallel to form a power module which can operate in a stable manner also in case of wide- bandgap semiconductor switches. More specifically, it is preferred to allow combination of semiconductor switches to form a multi-chip power module with parallel connected switches. Most preferably, multi-chip power modules that can operate to convert high power levels, such as in the 1-1000 kW range or more.

[0016] In a first aspect, the invention provides an electric power module comprising a plurality of external terminals, the power module comprising :

[0017] - at least first and second controllable semiconductor switches connected in parallel between the external terminals, such as SiC or GaN semiconductor switches, and

[0018] - at least one stabilizer circuit comprising a first resistor connected between the first and second terminals, wherein the first and second terminals of the stabilizer circuit are connected to:

[0019] 1) respective drain connections of the first and second controllable semiconductor switches, or

[0020] 2) respective source connections of the first and second controllable semiconductor switches, wherein the stabilizer circuit is configured to damp an electric high frequency oscillation in the power module, such as an oscillation within 1-1000 MHz.

[0021] Such power module is advantageous since it is possible to implement power modules to form power converters made up of one or more power modules with parallel connected GaN or SiC based semiconductor switches, e.g. in half bridge configuration or in other configurations. Due to the proposed stabilizer circuit(s), such power modules can be operated in a safe manner without any instability issues. In its simplest form the stabilizer circuit can be implemented as one or more resistors, preferably with a resistance of 1-100 Q.

[0022] The invention is based on the inventors' insight, that high frequency oscillations, 84544PC01

[0023] 3 e.g. in the range 1-1000 MHz, caused by parasitics lead to instability problems when parallel connecting wide-bandgap semiconductors. These high frequency oscillations disturb the function of parallel connected semiconductor switches and cause instability problems. The proposed stabilizer circuit(s) mitigates the high frequency oscillations and thereby mitigate the instability problems.

[0024] Since the stabilizer circuit is connected between the semiconductor components where there is a zero DC voltage difference, the stabilizer circuit, and especially its resistor, will absorb only high frequency energy, and thus the stabilizer circuit does not provide any significant power loss.

[0025] Further, an important advantage of the proposed stabilizer circuit is that it does not affect switching performance of the semiconductor switches, which is in contrast with snubber circuits.

[0026] In its simplest form, the stabilizer circuit can be implemented by a single resistor component, and it is therefore rather simple to implement. More preferably, two resistors are used per set of paralleled semiconductor switches. In some cases, two inductors may be used per resistor.

[0027] Normally, on a chip with a semiconductor switche, the the stabilizer circuit can be mounted directly to the chip connection points. However, in other embodiments, the stabilizer circuit may in addition or alternatively be mounted on external terminals of the power module.

[0028] In general, the stabilizer circuit(s) can be connected to internal terminals or connection points of the power module, but the stabilizer circuit(s) can alternatively or additionally be connected to external terminals of the power module.

[0029] The inventors have specifically tested a 7.2 kV / 200 A power module based on a multi-chip with altogether eight 10 kV SiC MOSFETs switches in a half-bridge configuration. Here, the proposed stabilizer circuits were used between each pairs of switches, and with these stabilizer circuits, a stable operation was observed even at high currents exceeding what has been previously achieved with these 84544PC01

[0030] 4 switches. Without stabilizer circuits, a 70 MHz oscillation was observed which caused instability problems.

[0031] In the following, preferred features and embodiments will be described.

[0032] Here and in the following "connected" means electrically connected.

[0033] Here and in the following "component X being connected between A and B" means that one terminal of component X is connected to A and another terminal of component X is connected to B.

[0034] By "AC output signal" is meant to include that the power circuit outputs a stepped voltage waveform which can approximate an AC signal.

[0035] In some embodiments, the power module comprises a stabilizer circuit with only first and second terminals, also called a two-port stabilizer circuit. Especially, the first resistor may be directly connected between the first and second terminals. In some embodiments, the first resistor and a first capacitor are connected in series between the first and second terminals. In some embodiments, the first resistor and a first inductor are connected in series between the first and second terminals.

[0036] In some embodiments, the power module comprises a stabilizer circuit comprising third and fourth terminals, and wherein said stabilizer circuit comprises first, second, third and fourth inductors which are connected to respective first, second, third and fourth terminals, wherein the first and second inductors are connected in series to form a first inductor pair, and wherein the third and fourth inductors are connected in series to form a second inductor pair. This embodiment is a four-port version of the stabilizer circuit. Especially, the first resistor may be directly connected between mid points of the first and second inductor pairs. Especially, the first resistor may form a series connection with a first capacitor, and wherein said series connection is connected between mid points of the first and second inductor pairs. 84544PC01

[0037] 5

[0038] In some embodiments, the af least first and second terminal of the at least one stabilizer circuit are connected to the first and second semiconductor switches via one or more of: a bond wire, a busbar, and a Direct Bonded Copper (DBC) substrate.

[0039] In some embodiments, the first and second terminals of the stabilizer circuit are connected to respective drain connections of the first and second controllable semiconductor switches.

[0040] In some embodiments, the first and second terminals of the stabilizer circuit are connected to respective source connections of the first and second controllable semiconductor switches.

[0041] In some embodiments, the power module comprises at least first and second stabilizer circuits each comprising first and second terminals and at least a first resistor connected between the first and second terminals. Especially, the first and second terminals of the first stabilizer circuit may be connected to respective drain connections of the first and second controllable semiconductor switches, and werein the first and second terminals of the second stabilizer circuit are connected to respective source connections of the first and second controllable semiconductor switches.

[0042] Thus, the power module can be stabilized by a stabilizer circuit connected to drains or to sources of the semiconductor switches, or it can be stabilized with respective stabilizer circuits connected to drains and to sources of the semiconductor switches.

[0043] In preferred embodiments, the first and second semiconductor switches are gallium nitride (GaN) or silicon carbide (SiC) semiconductor switches.

[0044] In some embodiments, the power module further comprises at least a third controllable semiconductor switch, such as a SiC or GaN semiconductor switch, and in some embodiments, the power module comprises at least four controllable semiconductor switches, such as at least four SiC or GaN semiconductor switches. Especially, the power module may comprise a parallel connection of at least three 84544PC01

[0045] 6 semiconductor switches between the external terminals. More specifically, the semiconductor switches are connected to form a half-bridge configuration between the external terminals.

[0046] In some embodiments, the power module comprises at least first and second sub switch groups each comprising at least first and second controllable semiconductor switches implemented on separate dies and connected in parallel, and wherein each of the first and second sub switch groups comprises respective first and second stabilizer circuits each comprising a resistor.

[0047] In a more specific embodiment, the power module comprises four sub switch groups each comprising two parallel connected controllable semiconductor switches, wherein the four sub switch groups are connected in a half-bridge configuration between first, second and third external terminals. More specifically, each of the four sub switch groups may be connected to a stabilizer circuit comprising at least a resistor. More specifically, one group of stabilizer circuits may be connected to drain connections of semiconductor switches of each of the four sub switch groups. More specifically, one group of stabilizer circuits may be connected to source connections of semiconductor switches of each of the four sub switch groups. More specifically, a first group of stabilizer circuits may be connected to drain connections of semiconductor switches of first and second sub switch groups and to a first external terminal, a second group of stabilizer circuits is connected to source connections of semiconductor switches of third and fourth sub switch groups and to a second external terminal, and a third group of stabilizer circuits is connected to and to a third external terminal. More specifically, a group of stabilizer circuits, wherein each stabilizer circuit in said group of stabilizer circuits has only two terminals. More specifically, a group of stabilizer circuits, wherein each stabilizer circuit in said group of stabilizer circuits has four terminals.

[0048] In an embodiment, the power module comprises four sub switch groups each comprising thre parallel connected controllable semiconductor switches, wherein the four sub switch groups are connected in a half-bridge configuration between first, second and third external terminals. 84544PC01

[0049] 7

[0050] The power module may comprise a plurality of sub power modules each with a plurality of semiconductor switches, wherein the plurality of sub power modules are interconnected in parallel between the external terminals, and wherein a stabilizer circuit comprising at least a resistor is connected to one or more of the interconnections of the sub power modules.

[0051] The first resistor preferably has a resistance of 1-100 Q, such as a resistance of 5- 80 Q, such as a resistance of 10-70 Q. It is to be understood that the most effective resistance for damping high frequency oscillations depends on the actual power module implementation and its components.

[0052] In some embodiments, the first and second semiconductor switches are implemented on respective dies which are mounted on a Direct Bonded Copper substrate, such as the Direct Bonded Copper substrate being mounted on a base plate.

[0053] In preferred embodiments, the first and second semiconductor switches are IGBTs or MOSFETs.

[0054] In some embodiments, the stabilizer circuit comprises a stabilizer module comprising a first module terminal arranged for connection to a first external terminal of the power module, a first inductor connected between the first module terminal and first terminal of a resistor, a second inductor connected between a second terminal of the first resistor, and a second module terminal arranged for connection to a second external terminal of the power module. More specifically, the first and second module terminals, the first and second inductors and the resistor are arranged on a circuit board.

[0055] The invention is applicable for power modules of a large variety of voltage handlings, such as at least 5 V, such as at least 30 V, such as at least 100 V, such as at least 500 V, such as at least 1 kV, such as at least 5 kV, such as at least 10 kV, such as at least 20 kV, such as at least 50 kV.

[0056] The invention is applicable for power modules of a large variety of power handling capacities, such as a power of at least 1 W, such as at least 10 W, such as at least 84544PC01

[0057] 8

[0058] 100 W, such as at least 1 kW, such as at least 10 kW, such as at least 20 kW, such as at least 50 kW, such as at least 100 kW, such as at least 1 MW.

[0059] The invention is applicable for power modules configured for operation of a large variety of switching frequencies, such as the first and second controllable semiconductor switches being configured for operation at a switching frequency of 1 kHz, such as at least 5 kHz, such as at least 10 kHz, such as at least 50 kHz, such as at least 100 kHz.

[0060] In some embodiments, the power module further comprises a diode, and wherein a stabilizer circuit comprising a resistor is connected to at least an anode connection or a cathode connection of the diode. Such stabilizer circuit connected the diode may in some cases help to damp unintended high frequency oscillations related to the diode.

[0061] The first resistor is preferably a Surface Mounted Device component or a chip resistor component, however in principle any resistor technology may be used.

[0062] Preferably, the first resistor is a component which is selected to have a low lead inductance, since even an inductance of the order of nH may in some cases be important in its role to damp a high frequency oscillation.

[0063] The semiconductor switches may especially be bidirectional two-quadrant switches may be implemented based on Si, SiC or GaN technology.

[0064] In some embodiments, the stabilizer circuit is implemented by one single resistor component, which has been proven to be sufficient in some application to dampen high frequency oscillations.

[0065] In preferred embodiments, the power module comprising a casing for housing the at least first and second controllable semiconductor switches and the at least one stabilizer circuit. Most preferably, the casing is a presspack casing.

[0066] By 'presspack' is understood a casing of the power module, where the semiconductor is pressed between two heatsinks, eliminating the need for weak 84544PC01

[0067] 9 components like solder and wire bonds for high reliability and power cycling capability. This design is preferred for high-power applications, such as electric grids and industrial converters, where it offers benefits such as low losses, efficient cooling, long-term reliability, and modularity for high current and voltage applications.

[0068] Furthermore, the presspack casing provides a high degree of safety, since explosion risk is eliminated, which is especially important if SiC or GaN semiconductor switches are used. Thus, a presspack based power module with e.g. SiC based switches combines high safety and high efficiency.

[0069] Most preferably, the first and second controllable semiconductor switches arranged inside the presspack casing are SiC based switches, such as SiC based MOSFETs.

[0070] In some embodiments, the at least first and second controllable semiconductor switches comprising at least 10 SiC based switches connected in parallel inside the presspack casing, such as 10-100 SiC based switches connected in parallel inside the presspack casing. Especially, the at least one stabilizer circuit may comprise a plurality of stabilizer circuits each comprising at least a resistor, wherein the plurality of stabilizer circuits are connected between:

[0071] 1) respective drain connections of at least a plurality of sets of the at least 10 SiC based switches, or

[0072] 2) respective source connections of at least a plurality of sets of the at least 10 SiC based switches.

[0073] In preferred embodiments, the power module comprises a stabilizer circuit connected between at least 10% of the at least 10 SiC based switches, such as at least 20% such as at least 30%, such as at least 40%, such as at least 50% of the at least 10 SiC based switches. Especially, all drain or source connections of the plurality of sets of the at least 10 SiC based switches may have a stabilizer circuit connected thereto.

[0074] The presspack casing may especially have a cylindrical or rectangular shape. 84544PC01

[0075] 10

[0076] Preferably, the presspack casing has an upper electrically conductive surface serving as a first external terminal, and a lower electrically conductive surface serving as a second external terminal.

[0077] The power module with a presspack casing may comprise a plurality of electrically conducting spring elements serving to connect the at least first and second controllable semiconductor switches (SW1, SW2) and first and second external terminals.

[0078] The power module with a presspack casing may be configured to handle a voltage of at least 1 kV at the external terminals, such as at least 5 kV, such as at least 10 kV. The power module with a presspack casing may be configured to handle a current of at least 100 A, through the external terminals, such as at least 200 A, such as at least 500 A, such as at least 1 kA.

[0079] In preferred embodiments, the power module with a presspack casing houses a plurality of SiC based chips each comprising at least one SiC based controllable switch inside the presspack casing.

[0080] The presspack casing preferably comprises a layered structure of a plurality of layers between an electrically conducting external upper layer and an electrically conducting external lower layer.

[0081] In a second aspect, the invention provides an electric power converter comprising an electric input arranged to receive an AC or a DC voltage and an electric output arranged to output an AC or a DC voltage, wherein the power converter comprises at least one power module according to the first aspect.

[0082] The power converter may comprise a plurality of power modules, such as 2-10, or more than 10. Especially, the plurality of power modules may be connected in parallel. Especially, the power converter may comprise at least one stabilizer circuit comprising a resistor connected to an interconnection of the plurality of parallel connected power modules, so as to damp a high frequency oscillation, e.g. 1-1000 MHz. More specifically, the power converter may comprise a plurality of stabilizer circuit each comprising a resistor, wherein the plurality of stabilizer 84544PC01

[0083] 11 circuits are connected to respective interconnection points of the plurality of parallel connected power modules. More specifically, the plurality of stabilizer circuits may comprise respective stabilizer circuits connected to all interconnection points between all of the parallel connected power modules. The stabilizer circuits referred to for the parallel connected power modules may especially be two-port stabilizer circuits, such as each implemented by one single resistor.

[0084] The power converter may be a DC-DC converter, a DC-AC converter, an AC-DC converter, or an AC-AC converter.

[0085] In some embodiments, the power converter comprises at least one power module comprising a casing for housing the at least first and second controllable semiconductor switches and the at least one stabilizer circuit. Most preferably, the casing is a presspack casing. Especially, the power converter may comprise a plurality of power modules according to the first aspect, wherein each of the plurality of power modules are housed in a presspack casing.

[0086] In a third aspect, the invention provides a method for damping high frequency oscillations, such as 1-1000 MHz oscillations, in an electric power module comprising first and second semiconductor switches, such as GaN or SiC based switches, connected in parallel between external terminals, the method comprising:

[0087] - providing at least one stabilizer circuit comprising at least a first resistor connected between the first and second terminals,

[0088] - connecting the stabilizer circuit between drain connections of the first and second controllable semiconductor switches or connecting the stabilizer circuit between source connections of the first and second controllable semiconductor switches,

[0089] - applying an input voltage at an external input terminal of the power module,

[0090] - operating the first and second controllabel semiconductor switches to switch according to a switching scheme, and

[0091] - generating an output voltage at an external output terminal accordingly.

[0092] Features and embodiments of the mentioned aspects of the present invention may each be combined with each other. These and other aspects of the invention will 84544PC01

[0093] 12 be apparent from and elucidated with reference to the embodiments described hereinafter.

[0094] BRIEF DESCRIPTION OF THE FIGURES

[0095] The present invention and in particular preferred embodiments thereof will now be disclosed in more detail with regard to the accompanying figures. The figures show ways of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0096] FIG. 1 illustrates an embodiment with two parallel semiconductor switches and one stabilizer circuit,

[0097] FIG. 2a and 2b illustrate other embodiments with one and two stabilizer circuits used on two parallel semiconductor switches,

[0098] FIG. 3a and 3b illustrate embodiments with stabilizer circuits used on switching arrangements with three or more parallel semiconductor switches,

[0099] FIG. 4a and 4b illustrate use of 4-port and 2-port stabilizer circuits on a halfbridge power module,

[0100] FIG. 5a, 5b and 5c illustrate different 2-port stabilizer circuit embodiments,

[0101] FIG. 6a and 6b illustrate different 4-port stabilizer circuit embodiments,

[0102] FIG. 7a, 7b and 7c illustrate for a half-bridge power module embodiment a circuit diagram and photos showing practical implementation of stabilizer circuits, FIG. 8a and 8b illustrate for another half-bridge power module a circuit diagram and a 3D view of an implementation,

[0103] FIG. 9a and 9b illustrate two power converter embodiments where a plurality of power modules are connected in parallel and with stabilizer circuits at their interconnections,

[0104] FIG. 10 illustrates steps of a method embodiment, and

[0105] FIG. 11-15 illustrate various drawings, a photo and a circuit diagram showing embodiments with implementation of power modules in a presspack casing. 84544PC01

[0106] 13

[0107] DETAILED DESCRIPTION OF EMBODIMENTS

[0108] FIG. 1 illustrates a power module embodiment with two parallel connected semiconductor switches SW1, SW2, e.g. GaN or SiC implemented on separate dies (indicated by dashed lines), and a stabilizer circuit SC with a resistor R_S connected directly between drain connections of the switches SW1, SW2.

[0109] The resistor R_s preferably has a resistance of 1-100 Q. Such resistance value has been found to be a suitable value for providing an efficient damping of high frequency oscillations which has been observed as a problem that can create instability of power modules with parallel connectred semiconductor switches.

[0110] High frequency oscillations have been observed in the frequency range typically in the frequency range 1-1000 MHz, often around 50-150 MHz.

[0111] In the shown embodiment the stabilizer circuit SC includes inductors which may be added to provide an even higher high frequency oscillation in some cases.

[0112] It is to be understood that the inductors in FIG. 1 may be specific components added, but in some cases the inductors can be parasitic inductances caused by the practical implementation of the power module, e.g. a busbar or an arrangement of the external terminal of the power module etc.

[0113] FIG. 2a illustrates another use of the same stabilizer circuit SC as in FIG. 1, but here the stabilizer circuit is connected directly between source connections of the switches.

[0114] FIG. 2b illustrates yet another variant of the embodiment of FIG. 1, namely with the same stabilizer circuit SC as in FIG. 1 duplicted, so there is a stabilizer circuit connected directly between the source connections of the switches and also a stabilizer circuit directly connected between drain connections of the switches which provides a higher degree of high frequency oscillation damping.

[0115] FIG. 3a and 3b illustrate power modules with three or more semiconductor switches connected in parallel, and with stabilizer circuits having resistors 84544PC01

[0116] 14 connected between all drain connections and resistors connected between all source connections of the semiconductor switches.

[0117] FIG. 4a illustrates a half-bridge power module with external terminals P, M being +DC and -DC, and an AC output terminal. Two sets of two parallel connected seminconductor switches are interconnected, and four stabilizer circuits SCI, SC2, SC3, SC4 with respective resistors connected to provide 4-port connections.

[0118] FIG. 4b illustrates another way of implementing stabilizer circuits in a similar power module as in FIG. 4a. Here, four 2-port stabilizer circuits SC1-4, e.g. each with only a resistor, connected close to both source connections and drain connections of the semiconductor pairs.

[0119] FIG. 5a, 5b and 5c illustrate various possible 2-port implementations of the stabilizer circuits, i.e. connection of elements between terminals A and B of the stabilizer circuit.

[0120] FIG. 5a has a resistor R directly connected between the terminals A and B.

[0121] FIG. 5b has a series connection of a resistor R and a capacitor C connected between the terminals A and B.

[0122] FIG. 5c has a series connection of a resistor R and an inductor L connected between the terminals A and B. As mentioned in relatetion to FIG. 1, the inductor L can be a physical component added, or it can represent a parasitic inductance.

[0123] FIG. 6a and 6b illustrate examples of 4-port implementation of the stabilizer circuits, i.e. connection of elements between stabilizer circuit terminals Al, A2, Bl and B2. Both embodiments has four inductors LI, L2, L3, L4 connected to the respective terminals Al, A2, Bl, B2.

[0124] FIG. 6a illustrates a stabilizer circuit embodiment where a resistor R connected to midpoints of each pairs of inductors LI, L3 and L2, L4 which are connected in series. 84544PC01

[0125] 15

[0126] FIG. 6b illustrates a stabilizer circuit embodiment with a series connection of a resistor R and a capacitor C is connected to midpoints of each pairs of inductors LI, L3 and L2, L4 which are connected in series.

[0127] FIG. 7a 7b and 7b illustrate a circuit diagram of a half-bridge power module embodiment and two photos showing practical implementation details of the stabilizer circuit.

[0128] FIG. 7a shows the half-bridge configuration of four sub-groups of two switches in parallel. External terminals are +DC, namely terminals PL and PR, -DC, namely terminals ML, MR, and output terminal AC.

[0129] As seen, stabilizer circuits SCI, SC2 each in the form of a resistor are here shown connected between the drain side (SCI) and between the source side (SC2) of the interconnected semiconductor swith sub-groups.

[0130] This embodiment has been tested to be stable due to the stabilizer circuits SCI, SC2. In a version with eight 10 kV SiC MOSFETs in a half-bridge configuration, the final module has been tested to be stable at all operation conditions up to a maximum voltage of 7.2 kV and a maximum switching current of 200 A. The switching waveforms, including the gate voltages, were tested to be clean and free of oscillations. Without stabilizer circuits the same power module is prone to oscillations around 70 MHz that will cause module failure at these voltage and current levels.

[0131] FIG. 7b shows a photo, see the dashed box, where the stabilizer circuit SC2 is implemented as chip Surface Mounted Device (SMD) resistors on -DC terminals ML, MR which are soldered on DBC islands and interconnected via a bond wire.

[0132] FIG. 7c shows a photo, see the dashed box, where a stabilizer circuit is implemented by a chip resistor soldered on a DBC island and connected to another DBC island via one wire bond.

[0133] Instead of chip resistors as shown in FIG. 7b and 7c, Surface Mounted Device (SMD) resistor components could be used, if preferred. 84544PC01

[0134] 16

[0135] FIG. 8a and 8b relate to another half-bridge based power module with an even higher power handling capacity than the embodiment of FIG. 7a-7c.

[0136] FIG. 8a shows a half-bridge configuration of four sub-groups of six switches in parallel, namely TL1-TL6, TR1-TR6, BL1-BL6, and BR1-BR6. External terminals are +DC, namely terminal P, -DC, namely terminal M, and two output terminals AC1, AC2.

[0137] Three stabilizer circuits SCI, SC2, SC3 are shown, each having a resistor in 2-port configuration. SCI is connected to drains of the upper two sub-groups TL1-TL6, TR1-TR6 of switches, and SC3 is connected to sources of the lower two subgroups BL1-BL6, BR1-BR6 of switches. One stabilizer circuit SC2 is connected at the interconnection between the upper and lower sub-groups of switches.

[0138] FIG. 8b shows a 3D view of the power module embodiment shown in FIG. 8a, where the four sub-groups each with six parallel connected switches are clearly seen.

[0139] FIG. 9a and 9b illustrate two power converter embodiments where a plurality of power modules PM1, PM2, PM3 are connected in parallel between external terminals P, M and AC. Terminal P is +DC, terminal M is -DC, and AC is an output terminal. All +DC, -DC and AC output terminals of the power modules PM1, PM2, PM3 are connected in parallel.

[0140] Even though each of the power modules PM1, PM2, PM3 have stabilizer circuits according to the invention, it has been found that parallel connection of power modules can lead to instability issues due to high frequency oscillations. Thus, in FIG. 9a and 9b two examples are given to use of stabilizer circuits SC, each comprising at least one resistor, at interconnection points of the power modules PM1, PM2, PM3.

[0141] In FIG. 9a two-port stabilizer circuits SC, e.g. implemented as in FIG. 5a, 5b or 5c, are connected at all interconnections of the power modules PM1, PM2, PM3, i.e. stabilizer circuits SC are connected between PM1 and PM2 on all of their +DC, 84544PC01

[0142] 17

[0143] -DC and AC output interconnections, and stabilizer circuits SC are connected between PM2 and PM3 on all of their +DC, -DC and AC output interconnections. Thus, six stabilizer circuits SC are used for the three parallel connected power modules PM1, PM2, PM3.

[0144] FIG. 9b shows a variant of FIG. 9a where two-port stabilizer circuits SC, e.g. implemented as in FIG. 5a, 5b or 5c, are connected to all interconnections of the power modules PM1, PM2, PM3, i.e. respective stabilizer circuits SC are connected with one port to +DC connections of the power modules PM1, PM2, PM3 and with their opposite ports being interconnected. The same applied to -DC and AC connections of the power modules PM1, PM2, PM3, thereby altogether using nine two-port stabilizer circuits SC for the three parallel connected power modules PM1, PM2, PM3.

[0145] FIG. 10 illustrate steps of a method embodiment, namely a method for damping high frequency oscillations, such as 1-1000 MHz oscillations, in an electric power module comprising first and second semiconductor switches, such as GaN or SiC based switches, connected in parallel between external terminals.

[0146] The method comprising providing SI at least one stabilizer circuit comprising at least a first resistor connected between the first and second terminals, either as a 2-port or as a 4-port. Next, connecting S2 the stabilizer circuit between drain connections of the first and second controllable semiconductor switches or connecting the stabilizer circuit between source connections of the first and second controllable semiconductor switches. This can be done by connecting using soldering directly on a DBC, a busbar or by means of bond wires. Next, applying S3 an input voltage at an external input terminal of the power module, and operating S4 the first and second controllabel semiconductor switches to switch according to a switching scheme, and thereby generating S5 an output voltage at an external output terminal accordingly.

[0147] FIG. 11 illustrates a power module housed in a presspack casing. In the illustrated embodiment, the presspack casing has a general cylindrical outer shape with a generally flat top provided by an upper external terminal ET_U and a generally flat bottom provided by a lower external terminal ET_L. 84544PC01

[0148] 18

[0149] Inside the presspack casing a plurality of SiC based chips CHP each with a semiconductor switch, here 52 SiC based semiconductor switches are illustrated as an example, e.g. SiC based MOSFETs. As seen, the SiC based chips CHP are arranged in a pattern constituting one plane parallel with the upper and lower extermanl terminals ET_U, ET_L

[0150] The presspack power module in FIG. 11 can handle for example a voltage of 10 kV and a current of more than 200 A, e.g. up to more than 1 kA.

[0151] In spite of the stabilizer circuit of the present invention, SiC based components can fail and even cause an explosion. The presspack casing provides a high degree of safety, since the SiC based chips CHP are enclosed and thus in case of a failure (even explosion) of one or more of the chips CHP, the presspack casing can protect against external damage.

[0152] FIG. 12 illustrates a photo of a prototype of a power module embodiment with a presspack casing having a generally rectangular shape.

[0153] FIG. 13 illustrates a cross section of a specific example of implementation of a presspack casing based on a conductive spring serving to provide electric connection between a semiconductor chip and a conductive Source pad and a conductive Drain pad. This can be a specific example of how to implement the presspack casings of FIG. 11 or 12.

[0154] The semiconductor chip is arranged on a gasket layer which connects to the Drain pad. On the opposite side of the semiconductor chip, a molybdenium layer and a copper layer connects to an electrically conductive spring which connects to the Source pad.

[0155] FIG. 14 and FIG. 15 show a circuit diagram and details of a layered structure of a power module embodiment with 12 SiC based MOSFETs arranged inside a presspack casing as also shown on the photo of FIG. 12. 84544PC01

[0156] 19

[0157] In FIG. 14, the SiC based switches are connected in parallel between external terminals T1 and T2, and stabilizer circuits SC are here shown as resistors connected between the parallel connection points of the SiC based switches.

[0158] In FIG. 15, the layered structure of the presspack is seen. Especially, the implementation of the stabilizer resistor R_SC is seen in the magnified image to the left. Here, the stabilizer resistor R_SC is seen to be a surface mounted resistor (SMD resistor) on conductive parts of a circuit board which are also connected, via spring connectors SP, to the parallel connection points of the source or the drain terminals of the semiconductor switches.

[0159] To sum up, the invention provides an electric power module with at least two semiconductor switches, e.g. SiC or GaN semiconductor switches, connected in parallel between external terminals. At least one stabilizer circuit with a resistor connected between the first and second terminals is connected to: drain connections of the both of the semiconductor switches, and / or both of the source connections of the semiconductor switches. The stabilizer circuit component(s) can be connected to internal or external terminals of the power module. The stabilizer circuit is configured to damp an electric high frequency oscillation in the power module, such as an oscillation within 1-1000 MHz. For example, the stabilizer circuit may be a resistor of 1-100 which has been found to damp high frequency oscillations in power modules caused by parasitics. The stabilizer circuit has been found to provide a high frequency oscillation damping effect to ensure a stable function of the power module. Since the stabilizer circuit is connected to connecting points with zero DC voltage difference, the power loss is minimal, and further the stabilizer circuit does not influence switching characteristics of the semiconductor switches. For high safety, the power module can be arranged inside a presspack casing.

[0160] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a 84544PC01

[0161] 20 plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

84544PC0121CLAIMS1. An electric power module comprising a plurality of external terminals, the power module comprising:- at least first and second controllable semiconductor switches (SW1, SW2) connected in parallel between the external terminals, such as SiC or GaN semiconductor switches, and- at least one stabilizer circuit (SC, SCI, SC2) comprising a first resistor (R_s) connected between a first and a second terminal (A, B), wherein the first and second terminals (A, B) of the stabilizer circuit (SC, SCI, SC2) are connected to:1) respective drain connections of the first and second controllable semiconductor switches (SW1, SW2), or2) respective source connections of the first and second controllable semiconductor switches (SW1, SW2), wherein the stabilizer circuit (SC, SCI, SC2) is configured to damp an electric high frequency oscillation in the power module, such as an oscillation within 1-1000 MHz.

2. The power module according to claim 1, comprising a stabilizer circuit with only first and second terminals.

3. The power module according to claim 2, wherein the first resistor is directly connected between the first and second terminals.

4. The power module according to claim 2, comprising a first capacitor, and wherein the first resistor and the first capacitor are connected in series between the first and second terminals.

5. The power module according to claim 2, comprising a first inductor, and wherein the first resistor and the first inductor are connected in series between the first and second terminals.84544PC01226. The power module according to any of the preceding claims, comprising a stabilizer circuit comprising third and fourth terminals, and wherein said stabilizer circuit comprises first, second, third and fourth inductors which are connected to respective first, second, third and fourth terminals, wherein the first and second inductors are connected in series to form a first inductor pair, and wherein the third and fourth inductors are connected in series to form a second inductor pair.

7. The power module according to claim 6, wherein the first resistor is directly connected between mid points of the first and second inductor pairs.

8. The power module according to claim 6, wherein the first resistor forms a series connection with a first capacitor, and wherein said series connection is connected between mid points of the first and second inductor pairs.

9. The power module according to any of the preceding claims, wherein the af least first and second terminal of the at least one stabilizer circuit are connected to the first and second semiconductor switches via one or more of: a bond wire, a busbar, and a Direct Bonded Copper substrate.

10. The power module according to any of the preceding claims, wherein the first and second terminals of the stabilizer circuit are connected to respective drain connections of the first and second controllable semiconductor switches.

11. The power module according to any of the preceding claims, wherein the first and second terminals of the stabilizer circuit are connected to respective source connections of the first and second controllable semiconductor switches.

12. The power module according to any of the preceding claims, comprising at least first and second stabilizer circuits each comprising first and second terminals and at least a first resistor connected between the first and second terminals.

13. The power module according to claim 12, wherein the first and second terminals of the first stabilizer circuit are connected to respective drain connections of the first and second controllable semiconductor switches, and84544PC0123 werein the first and second terminals of the second stabilizer circuit are connected to respective source connections of the first and second controllable semiconductor switches.

14. The power module according to any of the preceding claims, wherien the first and second semiconductor switches are gallium nitride or silicon carbide semiconductor switches.

15. The power module according to any of the preceding claims, comprising at least a third controllable semiconductor switch, such as a SiC or GaN semiconductor switch.

16. The power module according to any of the preceding claims, comprising at least four controllable semiconductor switches, such as at least four SiC or GaN semiconductor switches.

17. The power module according to claim 16, comprising a parallel connection of at least three semiconductor switches between the external terminals.

18. The power module according to any of claims 15-17, wherein semiconductor switches are connected to form a half-bridge configuration between the external terminals.

19. The power module according to any of claims 15-18, comprising at least first and second sub switch groups each comprising at least first and second controllable semiconductor switches implemented on separate dies and connected in parallel, and wherein each of the first and second sub switch groups comprises respective first and second stabilizer circuits each comprising a resistor.

20. The power module according to claim 19, comprising four sub switch groups each comprising two parallel connected controllable semiconductor switches, wherein the four sub switch groups are connected in a half-bridge configuration between first, second and third external terminals (M, P, AC).84544PC012421. The power module according to claim 20, wherein each of the four sub switch groups is connected to a stabilizer circuit comprising at least a resistor.

22. The power module according to claim 20 or 21, wherein one group of stabilizer circuits is connected to drain connections of semiconductor switches of each of the four sub switch groups.

23. The power module according to any of claims 20-22, wherein one group of stabilizer circuits is connected to source connections of semiconductor switches of each of the four sub switch groups.

24. The power module according to any of claims 20-23, wherein a first group of stabilizer circuits is connected to drain connections of semiconductor switches of first and second sub switch groups and to a first external terminal, a second group of stabilizer circuits is connected to source connections of semiconductor switches of third and fourth sub switch groups and to a second external terminal, and a third group of stabilizer circuits is connected to and to a third external terminal.

25. The power module according to any of claims 20-24, comprising a group of stabilizer circuits, wherein each stabilizer circuit in said group of stabilizer circuits has only two terminals.

26. The power module according to any of claims 20-25, comprising a group of stabilizer circuits, wherein each stabilizer circuit in said group of stabilizer circuits has four terminals.

27. The power module according to any of claims 20-26, comprising four sub switch groups each comprising thre parallel connected controllable semiconductor switches, wherein the four sub switch groups are connected in a half-bridge configuration between first, second and third external terminals (M, P, AC).

28. The power module according to any of the preceding claims, comprising a plurality of sub power modules each with a plurality of semiconductor switches, wherein the plurality of sub power modules are interconnected in parallel between the external terminals, and wherein a stabilizer circuit comprising at least a84544PC0125 resistor is connected to one or more of the interconnections of the sub power modules.

29. The power module according to any of the preceding claims, wherein the first resistor has a resistance of 1-100 Q, such as a resistance of 5-80 Q, such as a resistance of 10-70 Q.

30. The power module according to any of the preceding claims, wherein the first and second semiconductor switches are implemented on respective dies which are mounted on a Direct Bonded Copper substrate, such as the Direct Bonded Copper substrate being mounted on a base plate.

31. The power module according to any of the preceding claims, wherein the first and second semiconductor switches are IGBTs or MOSFETs.

32. The power module according to any of the preceding claims, wherein the stabilizer circuit comprises a stabilizer module comprising a first module terminal arranged for connection to a first external terminal of the power module, a first inductor connected between the first module terminal and first terminal of a resistor, a second inductor connected between a second terminal of the first resistor, and a second module terminal arranged for connection to a second external terminal of the power module.

33. The power module according to claim 32, wherein the first and second module terminals, the first and second inductors and the resistor are arranged on a circuit board.

34. The power module according to any of the preceding claims, being capable of handling a voltage of at least 5 V, such as at least 30 V, such as at least 100 V, such as at least 500 V, such as at least 1 kV, such as at least 5 kV, such as at least 10 kV, such as at least 20 kV, such as at least 50 kV.

35. The power module according to any of the preceding claims, being capable of handling an electric power of at least 1 W, such as at least 10 W, such as at least84544PC0126100 W, such as at least 1 kW, such as at least 10 kW, such as at least 20 kW, such as at least 50 kW, such as at least 100 kW, such as at least 1 MW.

36. The power module according to any of the preceding claims, wherein the first and second controllable semiconductor switches are configured for operation at a switching frequency of 1 kHz, such as at least 5 kHz, such as at least 10 kHz, such as at least 50 kHz, such as at least 100 kHz.

37. The power module according to any of the preceding claims, further comprising a diode, and wherein a stabilizer circuit comprising a resistor is connected to at least an anode connection or a cathode connection of the diode.

38. The power module according to any of the preceding claims, wherein the first resistor is a Surface Mounted Device component or a chip resistor component.

39. The power module according to any of the preceding claims, comprising a casing for housing the at least first and second controllable semiconductor switches (SW1, SW2) and the at least one stabilizer circuit (SC, SCI, SC2).

40. The power module according to claim 39, wherein the casing is a presspack casing.

41. The power module according to claim 39 or 40, wherein the first and second controllable semiconductor switches (SW1, SW2) are SiC based switches, such as SiC based MOSFETs.

42. The power module according to claim 39-41, wherein the at least first and second controllable semiconductor switches (SW, SW2) comprising at least 10 SiC based switches connected in parallel inside the presspack casing, such as 10-100 SiC based switches connected in parallel inside the presspack casing.

43. The power module according to claim 42, wherein the at least one stabilizer circuit comprises a plurality of stabilizer circuits each comprising at least a resistor, wherein the plurality of stabilizer circuits are connected between:84544PC01271) respective drain connections of at least a plurality of sets of the at least 10 SiC based switches, or2) respective source connections of at least a plurality of sets of the at least 10 SiC based switches.

44. The power module according to claim 43, comprising a stabilizer circuit connected between at least 10% of the at least 10 SiC based switches, such as at least 20% such as at least 30%, such as at least 40%, such as at least 50% of the at least 10 SiC based switches.

45. The power module according to any of claims 39-44, wherein the casing has a cylindrical or rectangular shape.

46. The power module according to any of claims 39-45, wherein the casing has an upper electrically conductive surface serving as a first external terminal, and a lower electrically conductive surface serving as a second external terminal.

47. The power module according to any of claims 39-46, comprising a plurality of electrically conducting spring elements serving to connect the at least first and second controllable semiconductor switches (SW1, SW2) and first and second external terminals.

48. The power module according to any of claims 39-47, wherein the power module is configured to handle a voltage of at least 1 kV at the external terminals, such as at least 5 kV, such as at least 10 kV.

49. The power module according to any of claims 39-48 wherein the power module is configured to handle a current of at least 100 A, through the external terminals, such as at least 200 A, such as at least 500 A, such as at least 1 kA.

50. The power module according to any of claims 39-49, wherein the casing houses a plurality of SiC based chips each comprising at least one SiC based controllable switch.84544PC012851. The power module according to any of claims 39-50, wherein the casing comprises a layered structure of a plurality of layers between an electrically conducting external upper layer and an electrically conducting external lower layer.

52. An electric power converter comprising an electric input arranged to receive an AC or a DC voltage and an electric output arranged to output an AC or a DC voltage, wherein the power converter comprises at least one power module (PM1, PM2, PM3) according to any of claims 1-51.

53. The power converter according to claim 52, comprising a plurality of power modules (PM1, PM2, PM3) according to any of claims 1-51.

54. The power converter according to claim 53, wherein the plurality of power modules (PM1, PM2, PM3) are connected in parallel.

55. The power converter according to claim 54, comprising at least one stabilizer circuit (SC) comprising a resistor connected to an interconnection of the plurality of parallel connected power modules (PM1, PM2, PM3).

56. The power converter according to claim 55, comprising a plurality of stabilizer circuit (SC) each comprising a resistor, wherein the plurality of stabilizer circuits (SC) are connected to respective interconnection points of the plurality of parallel connected power modules (PM1, PM2, PM3).

57. The power converter according to claim 56, wherein the plurality of stabilizer circuits (SC) comprise respective stabilizer circuits (SC) connected to all interconnection points between all of the parallel connected power modules (PM1, PM2, PM3).

58. The power converter according to any of claims 56 or 57, wherein the plurality of stabilizer circuits (SC) are two-port stabilizer circuits (SC).84544PC012959. The power converter according to any of claims 52-58, comprising an external input terminal arranged to receive a DC electric input, and an external output terminal arranged to output a DC electric output.

60. The power converter according to any of claims 52-58, comprising an external input terminal arranged to receive a DC electric input, and an output external terminal arranged to output a AC electric output.

61. The power converter according to any of claims 52-58, comprising a first external input terminal arranged for connection to a positive DC voltage, a second external input terminal arranged for connection to a negative DC voltage.

62. The power converter according to any of claims 52-58, comprising an input terminal arranged to receive a AC electric input, and an output terminal arranged to output a DC electric output.

63. The power converter according to any of claims 52-58, comprising an input terminal arranged to receive a AC electric input, and an output terminal arranged to output a AC electric output.

64. The power converter according to any of claims 52-63, comprising at least one power module according to any of claims 39-51.

65. The power converter according to any of claims 52-64, comprising a plurality of power modules according to any of claims 39-51.

66. A method for damping high frequency oscillations, such as 1-1000 MHz oscillations, in an electric power module comprising first and second controllable semiconductor switches, such as GaN or SiC based switches, connected in parallel between external terminals, the method comprising:- providing (SI) at least one stabilizer circuit comprising at least a first resistor connected between the first and second terminals,84544PC0130- connecting (S2) the stabilizer circuit between drain connections of the first and second controllable semiconductor switches or connecting the stabilizer circuit between source connections of the first and second controllable semiconductor switches,- applying (S3) an input voltage at an external input terminal of the power module,- operating (S4) the first and second controllable semiconductor switches to switch according to a switching scheme, and- generating (S5) an output voltage at an external output terminal accordingly.

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