SUBMODULE AND ASSOCIATED MODULE, TOWER, POWER CONVERTER, AND POWER SYSTEM

A submodule for a power converter is described. The submodule includes a first and a second power storage devices and a first stack of electronic device packages. The first stack includes a first, a second, a third, and a fourth electronic device package. A first power device and the first and second electronic device packages form a first half bridge converter, and a second power device and the third and fourth electronic device packages form a second half bridge converter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application Serial Number EP23161344.9, filed Mar. 10, 2023, which is herein incorporated by reference.

TECHNICAL FIELD

The present invention concerns power systems comprising power converters, and relates more particularly to a submodule for a power converter.

The present invention further relates to a module comprising such a submodule, a tower comprising such modules, and a power converter comprising such towers.

BACKGROUND

Power converters for example for oil and gas applications, traction drives and high-power conversion equipment, for example rectifiers, inverters, and for static synchronous compensator STATCOM typically include press-pack power devices.

Each press-pack power device includes for example insulated gate bipolar transistors IGBTs, MOSFET or Injection Enhanced Gate Transistor IEGT.

Generally, the press-pack power devices of a power converter are connected to power storage devices to form full bridge converters, each full bridge converter comprising a power storage device and four press-pack power devices.

For some applications, for example for some power conversion applications, the implementation of full bridge converters in a power converter is oversized, these applications only requiring the functionalities of half bridge converters.

A half bridge converter comprises a power storage device and only two press-pack power devices.

It is known to implement full bridge converters for applications requiring only half bridge converters.

However, the implementation of full bridge converters for applications requiring the functionalities of half bridge converters deteriorates the efficiency of the power converter and the complexity of the control circuit of the press-pack power devices.

As each full bridge converter comprising two times more press-pack power devices as a half bridge converter, the conduction losses generated by the IGBTs of the press-pack power devices are doubled and the number of IGBTs to control is doubled.

It is therefore proposed to remedy whole or some of the disadvantage related to power converters according to the prior art.

SUMMARY

In view of the foregoing the invention proposes a submodule for a power converter comprising a first and a second power storage devices and a first stack of electronic device packages, the first stack comprising a first, a second, a third, and a fourth electronic device packages, a first and a second end contact surfaces, and a first and a second terminals.

Each electronic device package comprises an upper contact surface, a lower contact surface, and controlled switch configured to control a current flowing between the upper contact surface and the lower contact surface of the said electronic device package.

The second electronic device package is sandwiched between the first and the third device packages, and the third device package is sandwiched between the second and the fourth device packages so that the upper contact surface of an electronic device package is operatively in contact with the lower contact surface of another electronic device package.

One contact surface of the upper and lower contact surfaces of the first electronic device package is operatively in contact with the second electronic device package, and the other contact surface of the upper and lower contact surfaces of the first electronic device package is the first end contact surface of the first stack, the first end contact surface being operatively in connected with a first end of the first power storage device, the first and second electronic device packages being operatively in contact with the first terminal.

One contact surface of the upper and lower contact surfaces of the fourth electronic device package is operatively in contact with the third electronic device package, and the other contact surface of the upper and lower contact surfaces of the fourth electronic device package is the second end contact surface of the first stack, the second end contact surface being operatively in contact with a first end of the second power storage device, the third and fourth electronic device packages being operatively in contact with the second terminal.

The surface of the upper and lower contact surfaces of the second electronic device package operatively in contact with the third electronic device package is further operatively in contact with the second end of the first and the second power storage devices.

The first power device and the first and second electronic device packages form a first half bridge converter, and the second power device and the third and fourth electronic device packages form a second half bridge converter.

Advantageously, the submodule comprising a first connection and a second connection, the first connection being connected to the first terminal of the first stack and the second connection being connected to the second terminal of the first stack.

Preferably, the submodule further comprises a first connection and a second connection, a wedge, a third and a fourth power storage devices, and a second stack of electronic device packages, the second stack comprising a fifth, a sixth, a seventh, and an eighth electronic device packages, a third and a fourth end contact surfaces, and a third and a fourth terminals.

The sixth electronic device package is sandwiched between the fifth and the seventh electronic device packages, and the seventh electronic device package is sandwiched between the sixth and the eighth electronic device packages so that the upper contact surface of an electronic device package is operatively in contact with the lower contact surface of the other electronic device package.

One contact surface of the upper and lower contact surfaces of the fifth electronic device package is operatively in contact with the sixth electronic device package, and the other contact surface of the upper and lower contact surfaces of the fifth electronic device package is the third end contact surface of the second stack, the third end contact surface being operatively in contact with a first end of the third power storage device, the fifth and sixth electronic device packages being operatively in contact with the third terminal.

One contact surface of the upper and lower contact surfaces of the eighth electronic device package is operatively in contact with the seventh electronic device package, and the other contact surface of the upper and lower contact surfaces of the eighth electronic device package is the fourth end contact surface of the second stack, the fourth end contact surface being operatively in contact with a first end of the fourth power storage device, the seventh and eighth electronic device packages being operatively in contact with the fourth terminal.

The surface of the upper and lower contact surfaces of the sixth electronic device package operatively in contact with the seventh electronic device package and is operatively in contact with the second end of the third and the fourth power storage devices.

The third power device and the fifth and sixth electronic device packages form a third half bridge converter, and the fourth power device and the seventh and eighth electronic device packages form a fourth half bridge converter.

The wedge is sandwiched between the first and the second stacks, one terminal of the first and second terminals being connected to one terminal of the third and fourth terminals, the other terminal of the first and second terminals being connected to the first connection and the other terminal of the third and fourth terminals being connected to the second connection.

Preferably, each power storage device comprises a housing, the housing being connected to the second end of the said power storage device.

Advantageously, when a half-bridge of the submodule is defect, the submodule further comprising a connection between the terminal associated with the defect half-bridge and the second end of the power storage devices associated with the defect half-bridge.

Preferably, each controlled switch comprises a field effect transistor or an Injection Enhanced Gate Transistor (IEGT).

Advantageously, the submodule further comprises electronic device package heatsinks, each electronic device package being sandwiched between two heatsinks, the heatsinks being configured to cool each electronic device package.

Another object of the invention relates to a module comprising a submodule as defined above and two compacting devices, each stack of the submodule being compacted between the two compacting devices. Preferably, each compacting device comprises an insulated plate in contact with a stack of the submodule, a pressure cone and a clamping plate, the pressure cone being sandwiched between the insulated plate and the clamping plate, a plurality of tie rods connecting the clamping plates of the two compacting devices.

Advantageously, each compacting device comprises an insulated plate in contact with a stack of the submodule and a pressure cone, the pressure cones of the two compacting devices being connected by a clamping bar.

Advantageously, the module comprises only the first stack, one of the clamping plates is connected to the second end of the power storage devices of the first stack.

Preferably, the module comprises the first stack and the second stack, one of the clamping plates is connected to the one terminal of the first and second terminals connected to one terminal of the third and fourth terminals.

Another object of the invention relates to a tower comprising a plurality of stacked modules as defined above, the electronic device packages of the modules being connected in series to form an arm for a multilevel power converter.

Another object of the invention relates to a power converter comprising at least a first tower as defined above and a second tower as defined above, both towers having a same number electronic device packages, the electronic device packages of the first tower forming an upper arm and the electronic device packages of the second tower forming a lower arm, the upper arm being operatively coupled to the lower arm via a connecting node to form a phase leg.

Advantageously, the power converter further comprises a controller configured to control the controlled switches.

Another object of the invention relates to a power system comprising a power source, a power converter as defined above, and a load or a source, the converter being configured to exchange electrical energy between the power source and the load or the source.

DETAILED DESCRIPTION

Specifically,FIG.1illustrates an example of a system1for performing power conversion.

The system1includes a source2, a multi-level power converter3, and a load/source4. The term source, as used herein, refers to a renewable power source, a non-renewable power source, a generator, a grid, a fuel cell, an energy storage (when discharged), and the like. Also, the term load, as used herein, may refer to a motor, an electrical appliance, an energy storage (when re-charged) and the like.

In addition, the power converter3may be a multilevel converter. The power source2may be operatively coupled to a first terminal (not shown) of the power converter3. A second terminal (not shown) of the power converter3may be operatively coupled to the source/load4. The first terminal and the second terminal may be alternatively employed as an input terminal or an output terminal of the power converter3.

The system1further includes a controller5. The controller5controls the operation of the power converter3by controlling switching of a plurality of controlled switches within modules of the power converter3.

The power source2may be a three-phase alternative current (AC) power source.

FIGS.2and3illustrate an example of the power converter3.

In particular,FIG.2illustrates a block diagram of the power converter3andFIG.3illustrates schematically an example of an arrangement of the modules of the power converter3.

InFIG.2, the power converter3has an ABC 3-phase structure including positive and negative direct current (DC) voltage rails6and7respectively.

The number of phases of the power converter3is identical to the number of phases of the power source2.

The positive and negative rails6and7form DC terminals8. Each of the 3-phases (A, B, and C) corresponds to one of phase legs9,10, and11.

Each phase of the power source2is connected to a different AC terminal12A,12B,12C of the power converter3.

A first phase leg9of the power converter3is connected to a first AC terminals12A, a second phase leg10is connected to a second AC terminals12B, and the third phase leg11is connected to a third AC terminals12C.

By way of example, the third phase leg11includes an upper arm13A and an identical lower arm13B. In the example ofFIG.2, the upper and lower arms (13A and13B) are connected together via a connecting node14, the connecting node14being connected to the third AC terminal12C.

The upper arm13A extends between the positive rail6and the connecting node14and the lower arm13B extends between the negative rail7and the connecting node14.

Each of the upper and lower arms13A,13B comprises a plurality of modules SM1-SMn and an arm inductor15A,15B.

The upper arm13A and the lower arm13B may comprise a same number of modules SM1-SMn.

Each module SM1-SMn comprises a first connection16A and a second connection16B.

The plurality of modules SM1-SMn of each arm13A,13B are connected in series so that the first connection16A of one module of one arm13A,13B is connected to the second connection16B of an adjacent module of the said arm.

The first remaining connection of the module SM1of the upper arm13A is connected to the positive rail6and the second remaining connection of the module SMn of the upper arm13A is connected to a first end of the inductor15A.

The second end of the inductor15A is connected to the connecting node14.

The first remaining connection of the module SM1of the lower arm13B is connected to a first end of the inductor15B.

The second end of the inductor15B is connected to the connecting node14.

The second remaining connection of the module SMn of the lower arm13B is connected to the negative rail7.

The remaining connection of a module is the end of the said module which is not connected to an end of another module.

In variant, the modules SM1-SMn of the upper arm13A are connected in series so that the second remaining connection of a module of the said arm is connected to the positive rail6and the modules SM1-SMn of the lower arm13B are connected in series so that the first remaining connection of a module of the said arm is connected to the negative rail7.

The discussion regarding the third phase leg11equally applies to the first and second phase legs9and10.

Each module of the modules SM1-SMn form two half-bridge converters.

For clarity reasons, it is assumed that each upper and lower arm13A,13B includes two modules SM1, SM2.

As the first, second and third phase legs9,10, and11are identical,FIG.3illustrates schematically an example of the arrangement of the modules SM1, SM2of the third phase leg11.

The modules SM1, SM2of the upper arm13A are stacked in a first tower17A and the modules SM1, SM2of the lower arm13B are stacked in a second tower17B.

The first tower17A and the second tower17B comprise the same number of modules SM1, SM2and may each comprise more than two modules SM1, SM2.

Each module SM1, SM2of the upper arm13A and lower arm13B comprises at least two half-bridge converters HB1, HB2.

The first connection16A of a first module SM1of the upper arm13A is connected to the positive rail6, the second connection16B is connected to the first connection16A of the second module SM2of the upper arm13A, and the second connection16B of the second module SM2is connected to the first end of the inductor15A of the upper arm13A.

The second end of the inductor15A of the upper arm13A is connected to the connecting node14.

The first connection16A of a first module SM1of the lower arm13B is connected to the first end of the inductor15B of the lower arm13B, the second connection16B is connected to the first connection16A of the second module SM2of the lower arm13B, and the second connection16B of the lower arm13B is connected to the negative rail7.

The second end of the inductor15B of the lower arm13B is connected to the connecting node14.

As each module SM1, SM2comprises at least two half bridge converters HB1, HB2, the power converter3made of modules SM1-SMn stacked in towers is more compact and need less space than a known power converter from the prior art.

As the modules SM1-SMn are identical,FIGS.4and5illustrate schematically a first exemplary embodiment of the module SM1.

In particular,FIG.4illustrates a first example of the arrangement of the module SM1andFIG.5illustrates an example of a block diagram of the module SM1associated to the first example of the arrangement of the module SM1.

InFIG.4, the module SM1comprises a first embodiment of a submodule18.

The submodule18comprises a first power storage device28, a second power storage device29, and a first stack30of electronic device packages comprising a first electronic device package31, a second electronic device package32, a third electronic device package33, and a fourth electronic device package34.

The first stack30is compacted between two compacting devices19,20.

Each compacting device19,20comprises an insulated plate21,22, a pressure cone23,24, and a clamping plate25,26.

The pressure cone23,24is sandwiched between the compaction plate21,22and the clamping plate25,26.

Each compaction plate21,22is in contact with a different end of the first stack30.

A plurality of tie rods27connect the two clamping plates25,26to maintain the first stack30compacted between the two compaction plates21,22.

The compacting devices19,20may be done differently, for example the compacting devices19,20may comprise the compaction plates21,22and the pressure cones23,24, the pressure cones23,24being connected by a clamping bar to maintain compacted the submodule18compacted between the two compaction plates21,22.

The first stack30further may comprise electronic device package heatsinks35so that each electronic device package31,32,33,34is sandwiched between two heatsinks35to cool each electronic device package.

The heatsinks35are made of an electrically conductive material, for example an aluminium alloy.

Each electronic device package31,32,33,34may be cylindrical and comprises an upper contact surface31a,32a,33a,34aand a lower contact surface31b,32b,33b,34bin contact with heatsinks35.

Each electronic device package31,32,33,34further comprises a controlled switch36,37,38,39(represented onFIG.5) controlled by the controller5and controlling a current flowing between the upper contact surface31a,32a,33a,34aand the lower contact surface31b,32b,33b,34bof the said electronic device package31,32,33,34.

Each controlled switch36,37,38,39may comprise a field effect transistor associated with an antiparallel power diode, for example an insulated gate bipolar transistor IGBT associated with an antiparallel power diode, an injection enhanced gate transistor IEGT associated with an antiparallel power diode, an integrated gate commutated thyristors IGCT associated with an antiparallel power diode or thyristors associated with an antiparallel power diodes and gate turn-off thyristor GTO associated with an antiparallel power diode.

The second electronic device package32is sandwiched between the first and the third device packages31,33.

The third device package33is sandwiched between the second and the fourth device packages33.

The electronic device packages31,32,33,34are stacked so that the upper contact surface of an electronic device package31,32,33,34is operatively in contact with the lower contact surface of an adjacent electronic device package.

A current flows between two contact surfaces operatively in contact or between a contact surface and a lead, even if the two surfaces or the contact surface and the lead are separated by part(s) made of an electrically conductive material, for example heatsink(s)35.

The contact surface of the first electronic device package31which is not operatively in contact with a contact surface of the second electronic device package32forms a first end contact surface of the first stack30and the contact surface of the fourth electronic device package34which is not operatively in contact with a contact surface of the third electronic device package33forms a second end contact surface of the first stack30.

For example, the upper contact surface32aof the second electronic device package32is operatively in contact with the lower contact surface of the first electronic device package31. The upper contact surface33aof the third electronic device package33is operatively in contact with the lower contact surface32bof the second electronic device package32. The upper contact surface34aof the fourth electronic device package34is operatively in contact with the lower contact surface33bof the third electronic device package33.

The upper contact surface31aof the first electronic device package31forms the first end contact surface and the lower contact surface34bof the fourth electronic device package34forms the second end contact surface.

The lower contact surface31bof the first electronic device package31and the upper contact surface32aof the second electronic device package32are operatively in contact with a first terminal40of the submodule18. The first terminal40is electrically in contact between the heatsinks35in contact with the lower contact surface31bof the first electronic device package31and with the upper contact surface32aof the second electronic device package32. The first terminal40may be connected to the first connection16A of the module SM1.

The lower contact surface33bof the third electronic device package33and the upper contact surface34aof the fourth electronic device package34are operatively in contact with a second terminal41of the submodule18. The second terminal41is electrically in contact between the heatsinks35in contact with the lower contact surface33bof the third electronic device package33and with the upper contact surface34aof the fourth electronic device package34. The second terminal41may be connected to the second connection16B of the module SM1.

The lower contact surface32bof the second electronic device package32and the upper contact surface33aof the third electronic device package33are operatively in contact with the second end of the first and second power storage devices28,29, and may be operatively in contact with a third terminal42of the submodule18.

The third terminal42of the first stack30and a first lead43are electrically in contact between the heatsinks35in contact with the lower contact surface32bof the second electronic device package32and with the upper contact surface33aof the third electronic device package33. The first lead43is connected to the second end of the first and second power storage devices28,29.

Each power storage devices28,29comprise one or more internal capacitor elements storing electric energy and may comprise a housing28a,29a.

The housing28aof the first power storage device28is connected to the second end of the said power storage device28, and the housing29aof the second power storage device29is connected to the second end of the said power storage device29.

A stray capacitance is formed between the internal capacitor elements of the power storage device28,29and the housing28a,29aof the said power storage device28,29. Such connexion enables to connect the stray capacitance in parallel to the internal capacitor elements of the said power storage device28,29so that the stray capacitance does not affects the switching behaviour of the controlled switches power electronics devices36,37,38,39, and does not generate stray currents during switching of the controlled switches36,37,38,39.

One of the two clamping plates25,26is connected to the second end of the power storage devices28,29.

The pressure cones23,24, the clamping plates25,26and the tie rods27may be made of electric conductive material such as steel.

The connection of one of the two clamping plates25,26to the second end of the power storage devices28,29reduces the voltage stress between the compacting device19comprising the pressure cones23,24, the clamping plates25,26and the tie rods27, and the elements of the stack30, in particular between the tie rods27and the heatsinks35.

In variant, the submodule18does not comprise the third terminal42.

The heatsink35in contact with the first end contact surface is connected with a second lead44to a first end of the first power storage device28. The second lead44is inserted between the said heatsink and the electrical insulating plate21.

The heatsink35in contact with the second end contact surface is connected with a third lead45to a first end of the second power storage device29. The third lead45is inserted between the said heatsink35and the electrical insulating plate22.

The first end contact surface is operatively in contact with the first end of the first power storage device28and the second end contact surface is operatively in contact with the first end of the second power storage device29.

FIG.5represents the controlled switches36,37,38,39connected with the first, second and third leads43,44,45to the first and second power storage devices28,29.

Each controlled switch36,37,38,39comprises a first connection36a,37a,38a,39aelectrically in contact with the upper surface31a,32a,33a,34aof the electronic device package31,32,33,34.

Each controlled switch36,37,38,39further comprises a second connection36b,37b,38b,39belectrically in contact with the lower surface31b,32b,33b,34bof the electronic device package31,32,33,34.

It is assumed that each controlled switch36,37,38,39comprises a field effect transistor50and an antiparallel power diode51.

The drain of the transistor50and the cathode of the antiparallel power diode51are connected to the second connection36b,37b,38b,39bof the controlled switch36,37,38,39.

The source of the transistor50and the anode of the antiparallel power diode51are connected to the first connection36a,37a,38a,39aof the controlled switch36,37,38,39.

The gate of the transistor50is connected to the controller5.

The controlled switch36of the first electronic device package31, the controlled switch37of the second electronic device package32, and the first power device28form the first half bridge converter HB1.

Similarly, the controlled switch38of the third electronic device package33, the controlled switch39of the fourth electronic device package34, and the second power device29form the second half bridge converter HB2.

When the module SM1comprises the third terminal42, if the first half bridge converter HB1is defect, a connection is established between the first terminal40and the third terminal42to bypass the defect first half bridge converter HB so that the module SM1is still transferring electrical energy between the first and second terminals40,41.

Similarly, if the second half bridge converter HB2is defect, a connection is established between the second terminal41and the third terminal42to bypass the defect second half bridge converter HB2.

As the modules SM1-SMn are identical,FIGS.6and7illustrate schematically a second exemplary embodiment of the module SM1.

FIG.6illustrates a second example of the arrangement of the module SM1andFIG.7illustrates an example of a block diagram of the module SM1associated to the second example of the arrangement of the module SM1.

InFIG.6, the module SM1comprises a second embodiment of the submodule18comprising four half bridge converters.

The submodule18is compacted between the two compacting devices19,20.

The submodule18comprises the first stack30, the first and second power devices28,29, the first, second, and third the leads43,44,45and the first, second and third terminals40,41,42as described above.

The submodule18further comprises a second stack60of electronic device packages61,62,63,64, a wedge65, a third power storage device66, and a fourth power storage device67.

Each electronic device package61,62,63,64may be cylindrical and comprises an upper contact surface61a,62a,63a,64aand a lower contact surface61b,62b,63b,64bin contact with heatsinks35.

Each electronic device package61,62,63,64further comprises a controlled switch68,69,70,71(represented onFIG.7) controlled by the controller5and controlling a current flowing between the upper contact surface61a,62a,63a,64aand the lower contact surface61b,62b,63b,64bof the said electronic device package61,62,63,64.

Each controlled switch61,62,63,64may comprise a field effect transistor associated with an antiparallel power diode, for example an insulated gate bipolar transistor IGBT associated with an antiparallel power diode, an injection enhanced gate transistor IEGT associated with an antiparallel power diode, an integrated gate commutated thyristors IGCT associated with an antiparallel power diode or thyristors associated with an antiparallel power diodes and gate turn-off thyristor GTO associated with an antiparallel power diode.

The sixth electronic device package62is sandwiched between the fifth and the seventh device packages61,63.

The seventh device package63is sandwiched between the sixth and the eighth device packages62,64.

The electronic device packages61,62,63,64are stacked so that the upper contact surface of an electronic device package61,62,63,64is operatively in contact with the lower contact surface of an adjacent electronic device package.

The contact surface of the fifth electronic device package61which is not operatively in contact with a contact surface of the sixth electronic device package62forms a third end contact surface of the second stack60and the contact surface of the eighth electronic device package64which is not operatively in contact with a contact surface of the seventh electronic device package63forms a fourth end contact surface of the second stack60.

For example, the upper contact surface62aof the sixth electronic device package62is operatively in contact with the lower contact surface61bof the fifth electronic device package61. The upper17contact surface63aof the seventh electronic device package63is operatively in contact with the lower contact surface62bof the sixth electronic device package62. The upper contact surface64aof the eighth electronic device package64is operatively in contact with the lower contact surface63bof the seventh electronic device package63.

The upper contact surface61aof the fifth electronic device package61forms the third end contact surface and the lower contact surface64bof the eight electronic device package64forms the fourth end contact surface.

The lower contact surface61bof the fifth electronic device package61and the upper contact surface62aof the sixth electronic device package62are operatively in contact with a fourth terminal72of the submodule18. The fourth terminal72is electrically in contact between the heatsinks35in contact with the lower contact surface61bof the fifth electronic device package61and with the upper contact surface62aof the sixth electronic device package62.

The lower contact surface63bof the seventh electronic device package63and the upper contact surface64aof the eighth electronic device package64are operatively in contact with a fifth terminal73of the submodule18. The fifth terminal73is electrically in contact between the heatsinks35in contact with the lower contact surface63bof the seventh electronic device package63and with the upper contact surface64aof the eighth electronic device package64.

The lower contact surface62bof the fifth electronic device package62and the upper contact surface63aof the seventh electronic device package63are operatively in contact with a second end of the third and fourth power storage devices66,67, and may be operatively in contact with a sixth terminal74of the submodule18.

The sixth terminal74of the second stack60and a fourth lead75are electrically in contact between the heatsinks35in contact with the lower contact surface62bof the sixth electronic device package62and with the upper contact surface63aof the seventh electronic device package63. The fourth lead75is connected to a second end of the third and fourth power storage devices66,67.

In variant, the submodule18does not comprise the sixth terminal74.

The wedge65is sandwich between the first and second stacks30,60.

The wedge65is made of an electrically non-conductive material or comprises electrical insulating layers so that a current does not flow through the wedge65.

It is assumed that the wedge65is made of an electrically non-conductive material.

In this embodiment, the heatsink35in contact with the third end contact surface of the first stack30is sandwiched between a first face of the wedge65and the fourth electronic device package34.

The third lead45is inserted between the said heatsink35and the first face the wedge65and is connected to the first end of the second power storage device29.

The heatsink35in contact with the third end contact surface of the second stack60is sandwiched between a second face of the wedge65and the fifth electronic device package61.

The second face of the wedge65is opposite to the first face.

A fifth lead76is inserted between the said heatsink35and the second face of the wedge65and is connected to the first end of the third power storage device66.

The heatsink35in contact with the fourth end contact surface is sandwiched between the eighth electronic device package64and the second insulated plate22, the electrical insulating being inserted between the said heatsink35and the second insulated plate22. A sixth lead77is inserted between the said heatsink35and the second insulated plate22, and connects the said heatsink35to the first end of the fourth power storage device67.

The third end contact surface is operatively in contact with the first end of the third power storage device66and the fourth end contact surface is operatively in contact with the first end of the fourth power storage device67.

The first terminal40is connected to the first connection16A of the module SM1, the second terminal41is connected to the fourth terminal72, and the fifth terminal73is connected to the second connection16B of the module SM1.

Each power storage devices66,67may comprise one or more internal capacitor elements storing electric energy and a housing66a,67a.

The housing66aof the third power storage device66is connected to the second end of the said power storage device66, and the housing67aof the fourth power storage device67is connected to the second end of the said power storage device67.

A stray capacitance is formed between the internal capacitor elements of the power storage device66,67and the housing66a,67aof the said power storage device66,67. Such connexion enables to connect the stray capacitance in parallel to the internal capacitor elements of the said power storage device66,67so that the stray capacitance does not affects the switching behaviour of the controlled switches68,69,70,71, and does not generate stray currents during switching of the controlled switches68,69,70,71.

One of the two clamping plates25,26is connected to the second terminal41and the fourth terminal72to reduce the voltage stress between the compacting device19comprising the pressure cones23,24, the clamping plates25,26and the tie rods27, and the elements of the stacks30,60, in particular between the tie rods27and the heatsinks35.

FIG.7represents the controlled switches36,37,38,39,68,69,70,71connected with the leads43,44,45,75,76,77to the first, second, third and fourth power storage devices28,29,66,67.

The controlled switches36,37,38,39,68,69,70,71of the first and the second stacks30,60may be identical.

Each controlled switch68,69,70,71comprises a first connection68a,69a,70a,71aelectrically in contact with the upper surface61a,62a,63a,64aof the electronic device package61,62,63,64.

Each controlled switch68,69,70,71further comprises a second connection68b,69b,70b,71belectrically in contact with the lower surface61b,62b,63b,64bof the electronic device package61,62,63,64.

It is assumed that each controlled switch68,69,70,71comprises the field effect transistor50and the antiparallel power diode51.

The drain of the transistor50and the cathode of the antiparallel power diode51are connected to the second connection68b,69b,70b,71bof the controlled switch68,69,70,71.

The source of the transistor50and the anode of the antiparallel power diode51are connected to the first connection68a,69a,70a,71aof the controlled switch68,69,70,71.

The gate of the transistor50is connected to the controller5.

The controlled switch68of the fifth electronic device package61, the controlled switch69of the sixth electronic device package62, and the third power device66form a third half bridge converter HB3. Similarly, the controlled switch70of the seventh electronic device package63, the controlled switch71of the eighth electronic device package64, and the fourth power device67form the fourth half bridge converter HB4.

When the module SM1comprises the sixth terminal74, if the third half bridge converter HB3is defect, a connection is established between the fourth terminal72and the sixth terminal74to bypass the defect third half bridge converter HB3so that the module SM1is still transferring electrical energy between the first and fifth terminals40,73.

Similarly, if the fourth half bridge converter HB4is defect, a connection is established between the sixth terminal74and the fifth terminal73to bypass the defect fourth half bridge converter HB4.

The second embodiment of the module SM1-SMn comprises four half bridge converters so that the towers17A and17B comprise even more half bridge converters.