WO2015188882A1

WO2015188882A1 - Arrangement for subsea housing of electric components and manufacturing of the same

Info

Publication number: WO2015188882A1
Application number: PCT/EP2014/062444
Authority: WO
Inventors: Cedric Bessire; Christian Spindler
Original assignee: ABB Technology AG
Current assignee: ABB Technology AG
Priority date: 2014-06-13
Filing date: 2014-06-13
Publication date: 2015-12-17
Anticipated expiration: 2016-12-13

Abstract

There is provided an arrangement for subsea housing of electric components. The arrangement comprises a rigid housing, the rigid housing being filled with a dielectric fluid. The arrangement comprises at least one electric component, the at least one electric component being provided inside the rigid housing. The rigid housing comprises pressure-volume means arranged to enable a volume change of the rigid housing.

Description

ARRANGEMENT FOR SUBSEA HOUSING OF ELECTRIC COMPONENTS AND MANUFACTURING OF THE SAME

TECHNICAL FIELD

Embodiments presented herein relate to housing of electric components, and particularly to an arrangement for subsea housing of electric components. Embodiments presented herein further relate to manufacturing of such an arrangement.

BACKGROUND

Packaging is essential for semiconductors in order to connect them

electrically and protect them from environmental influence. This is in particular the case for power semiconductors that are employed as main switching elements in various applications such as frequency converters which are used to drive motors in pumps, compressors etc.

Frequency converters in the medium voltage and high power range drive electric motors by controlling the speed and torque of these machines and are a well proven equipment in the entire onshore as well as offshore platform based industry. In recent years, growing interest has been laid on installing electrical installations on the sea floor in depths from a few tens of meters to even kilometers. One main driver of this development is the oil and gas industry, but future applications are seen in subsea high-voltage, direct current or high voltage alternating current transmission and distribution systems as well as offshore power generation (such as wind energy, tidal energy, wave energy, ocean current energy).

Subsea oil and gas production employs electric equipment such as drilling motors, pumps, and compressors that are currently driven by frequency converters located on topside platforms. Electric power is provided to the subsea machinery by expensive umbilical cords. By installing frequency converters and other power electronic equipment (such as insulated-gate bipolar transistor (IGBT) power semiconductor elements) subsea, cables and topside installations could be spared and enormous cost savings could be achieved.

In general terms, electric subsea installations and devices usually demand high standards regarding durability, long-term functionality and

independence during operation.

Thus, whilst currently the semiconductor module housing for the power electronic equipment is open to air, for applications in a liquefied and pressurized environment (as it is the case in a subsea converter installation at the bottom of the ocean) certain adjustments would be required in order to protect the silicon (Si) chip of the power semiconductor elements. In bringing power electronic equipment to be part of subsea applications, two general concepts currently exist.

According to a first concept the power electronic equipment stays at atmospheric pressure. This is realized in pilot plants today. This first concept allows standard electric/electronic components, known from onshore installations, to be used. However, thick walls are needed for the enclosure to withstand the pressure difference between inside and outside the tank as the tank is submerged into the ocean. Thick walls make the equipment heavy and costly. In addition, heat transfer through thick walls is not very efficient. Additionally, huge and expensive cooling units are required. This concept may thus be regarded as an open solution with a dielectric liquid.

According to a second concept the equipment is passively pressurized to the hydrostatic pressure level of the ambient sea water (increasing by 1 bar each 10 m, typically 100 to 300 bar for subsea installations under consideration). This is achieved by filling a thin-walled vessel with liquid of negligible compressibility. This is still in early development. This second concept does not require any thick walls for enclosure since no pressure difference exists between inside and outside the containment. Cooling is greatly facilitated by thin walls. This requires all the components to be free of gas inclusions and compressible voids. Otherwise they may implode during pressurization and thus be destroyed. Dielectric liquid must be stable over time in order to keep its insulating behavior during the entire time of operation. Further, impurities may evolve over time in the dielectric liquid used within the thin- walled vessel. If this dielectric liquid directly touches the termination on the silicon (Si) chip the impurities risk triggering a high peak field that may destroy the Si chip. This may become a reliability issue that (only) affects the semiconductor modules after some time in operation in a liquid

environment. The second concept may thus be regarded as a hermetically closed package solution. Hence, there is still a need for improved arrangements for subsea housing of electric components.

SUMMARY

An object of embodiments herein is to provide improved arrangements for subsea housing of electric components. A particular object is to provide an arrangement for subsea housing of electric components combining the advantages of the above presented first concept and second concept whilst still avoiding disadvantages of the above presented first concept and second concept.

According to a first aspect there is presented arrangement for subsea housing of electric components. The arrangement comprises a rigid housing, the rigid housing being filled with a dielectric fluid. The arrangement comprises at least one electric component, the at least one electric component being provided inside the rigid housing. The rigid housing comprises pressure- volume means arranged to enable a volume change of the rigid housing. Advantageously this provides an improved arrangement for subsea housing of electric components.

Advantageously this arrangement combines advantages of the above disclosed first concept and second concept. According to a second aspect there is presented a method of manufacturing an arrangement according to the first aspect. The method comprises providing a rigid housing, wherein the rigid housing comprises pressure- volume means arranged to enable a volume change of the rigid housing. The method comprises providing at least one electric component inside the rigid housing. The method comprises filling the rigid housing with a dielectric fluid.

According to an embodiment the method comprises lowering the housing into a body of water. The body of water may be an ocean or a lake. It is to be noted that any feature of the first and second aspects may be applied to any other aspect, wherever appropriate. Likewise, any advantage of the first aspect may equally apply to the second aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed

embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

Fig 1 is a schematic diagram illustrating a semiconductor module according to the state of the art;

Figs 2, 3, and 4 are schematic diagrams illustrating an arrangement 20 for subsea housing of electric components according to embodiments; and Fig 5 is a flowchart of methods according to embodiments. DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

The present invention relates to sealed pressure tolerant power

semiconductor modules suitable for subsea power systems.

A cross-sectional sketch of a typical known insulated-gate bipolar transistor (IGBT) semiconductor module 10 is shown in Fig 1. The semiconductor module 10 comprises a top plate 11 forming a module lid. The top plate 11 may be made of metal, such as copper. The semiconductor module 10 further comprises inner sidewalls 12 forming a semiconductor module frame. The side walls may be made of a polymer or polymeric substance. The

semiconductor module 10 further comprises at least one electric component 16 in the form of a silicon (Si) chip. Each of the at least one electric component 16 has a current bypass 13 and a spring washer pack 14 and is attached to a base plate 18. The semiconductor module 10 further comprises outer sidewalls 15 forming a module outer frame. The outer sidewalls 15 may be made of a fiberglass reinforced polymer. The bottom part of the semiconductor module 10 is filled with silicon gel 17 so as to enclose the at least one electric component 16.

Fig 2 schematically illustrates an arrangement 20 for subsea housing of electric components according to an embodiment. The arrangement 20 comprises a rigid housing 21. The rigid housing 21 is filled with a dielectric fluid 17. The arrangement 20 further comprises at least one electric component 16. The at least one electric component 16 is provided inside the rigid housing 21. The rigid housing 21 further comprises pressure-volume means 22. The pressure-volume means 22 are arranged to enable a volume change of the rigid housing. The arrangement 20 may thus define a semiconductor module and each at least one electric component 16 may define a semiconductor module.

The rigid housing 21 thus exhibits hermeticity against liquid that does not allow an external fluid or liquid to enter the semiconductor module defined by the arrangement 20 but simultaneously transfers the hydrostatic pressure outside the semiconductor module to the at least one electric component 16.

The present arrangement 20 thereby provides an ideal solution for enabling semiconductor modules to operate in a pressurized environment without the issue of handling any external fluid or liquid around the at least one electric component 16.

When submerged in an external fluid or liquid environment the present arrangement 20 enables to maintain the advantages of the well-known silicone gel within the semiconductor module without any pollution from the surrounding fluid or liquid environment and with a pressure transfer from the outside to the at least one electric component 16 such that the rigid housing withstands (very) high hydrostatic pressures.

In view of the semiconductor module 10 of Fig 1, the present arrangement 20 requires a modification to the housing of the at least one electric component 16 but on the other hand guarantees operation under high hydrostatic pressure and fluid or liquid environments and thus makes the arrangement 20 tolerant to both fluid or liquid and pressure.

Embodiments relating to further details of arrangements 20 for subsea housing of electric components will now be disclosed. There are different materials that could be used for forming the rigid housing 21. For example, the rigid housing 21 may be made of ceramic. For example, the rigid housing 21 may be made of plastic, such as reinforced plastic. There may be different possible shapes of the rigid housing 21. For example, a round or a squared rigid housing may be preferable since round or squared structures are robust against external forces acting on its surface, which could be the case during, for example, lowering or raising the rigid housing 21 for a deep sea environment- There are different materials that could be suitable for use as a dielectric fluid 17. For example, the dielectric fluid 17 may be a silicon gel.

There are different examples of electric components 16 that could be provided inside the rigid housing 21. For example, each one of the at least one electric component 16 may be part of a semiconductor module. For example, each one of the at least one electric component 16 may be part of an insulated-gate bipolar transistor (IGBT) power semiconductor element comprising a Si chip. The at least one electric component 16 may comprise a first electrical connector 16a and a second electrical connector 16b. The first electrical connector 16a may be an emitter contact plate, and the second electrical connector 16b may be a collector contact plate. The pressure-volume means 22 may be expansion joints. For example, a ceramic or plastic rigid housing 21 may be joined to metallic expansion joints using brazing technology.

The rigid housing 21 may comprise a base plate 18, side walls 12, and a top plate 11. The top plate 11 may form a lid to the at least one electric component 16. The pressure-volume means 22 may be provided between the bottom plate 18 and the side walls 12. Alternatively, and as illustrated in Fig 2, the pressure-volume means 22 may be provided between the side walls 12 and the top plate 11. The side walls 12 of the rigid housing 21 may thus have to be shorter than the module outer frame, such that the pressure-volume means 22 may be placed on top of the the side walls 12, as shown in Fig 2. The rigid housing 21 may thus be hermetically sealed. For example, intersections between the base plate 18, side walls 12, top plate 11, and pressure-volume means 22 may be joined by sealed junctions 23a, 23b, 23c. For example, the lid (as formed by the top plate 11) may be welded to the expansion joints (as formed by the pressure-volume means 22) to close the rigid housing 21. The connection from side walls 12 to the base plate 18 can be brazed as well in order to seal the connection and make it liquid tight. The at least one electric component 16 may be attached to the base plate 18 of the rigid housing 21.

Hermetically sealing the rigid housing 21 prevents the at least one electric component 16 from cross-contamination by an external fluid or liquid.

Protection may be paramount due to the sensitive edge termination of the IGBT (if such an electric component 16 is used). The sealing is achieved by attaching the side walls 12 made from a hermetic material, such as ceramic or a plastic (such as a reinforced plastic), around the at least one electric component 16 directly on the base plate 18 as illustrated in Fig 2. Such a sealed rigid housing 21 does not allow any liquid to enter the interior of the rigid housing 21 and the dielectric fluid 17 fills the complete interior of the rigid housing 21 (not occupied by the at least one electric component 16, etc.) for dielectric protection. On lowering such a rigid housing 21, for example, to a sea bed, the increasing hydrostatic pressure compresses the rigid housing 21 via the pressure-volume means 22 such that the pressure inside the rigid housing 21 adapts to the environmental pressure. When the at least one electric component 16 heats up during operation, the dielectric fluid 17 may expand by relaxing the pressure-volume means 22.

Fig 3 schematically illustrates an arrangement 20 where the rigid housing 21 is clamped between a clamp top piece 33 and a clamp bottom piece 34 with a certain force in order to establish well conducting, dry, contacts within the rigid housing 21. Since the rigid housing 21 including the pressure-volume means 22 is flexible, it will alter its height depending on pressure and internal temperature. At the same time, electrical connection, for example by means of a bus bar 31, to the top lid must be guaranteed at any time. This could be achieved by attaching a flexible, spring-like bus bar 31 as illustrated in Fig 3. The arrangement 20 may thus further comprise a bus bar 31. The bus bar 31 is provided outside the rigid housing 21 and has a flexible portion 32. The flexible portion 32 is electrically connected to the first electrical connector 16a of the at least one electric component 16. A flexible end termination of the otherwise rigid bus bar 31 may thus allow a movable top plate 11.

The arrangement 20 of Fig 3 further comprises a heat sink 35. A heat sink 35 may be provided outside the rigid housing 21 and thermally connected to either the top plate 11 or the bottom plate 18 (as in Fig 3). Alternatively a further heat sink (not illustrated) is thermally connected to the other of the top plate 11 and the bottom plate 18. The rigid housing 21 may thus, together with at least one heat sink 35 be sandwiched between a clamp top piece 33 and a clamp bottom piece 34.

In order to withstand the internal pressure inside the rigid housing 21 during the lowering of the arrangement 20 towards, for example, a sea bottom, springs 24 can be used. For example, each one of the at least one electric component 16 may be associated with a spring 24. Hence the arrangement 20 may further comprise at least one spring 24. The at least one spring 24 is thus provided in the rigid housing 21. Each spring 24 is arranged to extend between a respective electric component 16 and the top plate 11 of the rigid housing 21. In the pre-clamping, 15-20 kN may be applied to each rigid housing 21. The additional clamping force that is due to the pressure of (maximum) 300 bars at the bottom of the ocean will generate a force of about 90 kN on each rigid housing 21. This additional force can be compensated by the springs 24. Furthermore, another repelling force will come from the dielectric fluid 17 that is pressed together in the rigid housing 21 and thus generates a certain pressure in the rigid housing 21 as well. The internal pressure will always be a bit lower than the surrounding pressure due to the additional springs 24 in the rigid housing 21. However this pressure difference is not severe for the rigid housing 21, since ceramic and

(reinforced) plastic can withstand such a pressure difference.

Reference is now made to Fig 5 illustrating a method for manufacturing an arrangement 20 for subsea housing of electric components according to embodiments.

The method comprises in a step S102 providing a rigid housing 21. The rigid housing comprises pressure-volume means 22 arranged to enable a volume change of the rigid housing 21. The method comprises in a step S104 providing at least one electric component 16 inside the rigid housing 21. The method comprises in a step S106 filling the rigid housing 21 with a dielectric fluid 17.

The method may comprise an optional step S108 of lowering the rigid housing into a body of water. The body of water may be an ocean or a lake.

Further details of the method for manufacturing an arrangement 20 for subsea housing of electric components will now be disclosed.

Firstly, a rigid housing 21 may be provided as in step S102. The rigid housing 21 may be provided with holes 41a, 41b, as illustrated in Fig 4.

Secondly, at least one electric component 16 may be provided as in step S104. The at least one electric component 16 and/or the rigid housing 21 may be thermally connected to a heat sink 35, and the at least one electric component 16 may be electrically connected to a bus bar 31. As disclosed above, in order to let the pressure-volume means 22 work at all time the bus bar 31 has a flexible portion 32 electrically connected to the first electrical connector 16a of the at least one electric component 16, such that the top plate 11 of the rigid housing 21 is movable.

Thirdly, the arrangement 20 may be provided with clamps 33, 34 so as to clamp the rigid housing 21 with a lowest possible force that guarantees a reliable dry contact under atmospheric ambient pressure, e.g. 15 kN. Fourthly, the rigid housing 21 is filled with a dielectric fluid 17 as in step S106. This dielectric fluid 17 is filled through at least one of the holes 41a, 41b at the side of the rigid housing 21 that will be hermetically sealed after the completion of the filling process. The interior of the rigid housing 21 is completely filled with dielectric fluid 17 for dielectric protection of the at least one electric component 16.

In more detail, the filling of the dielectric fluid 17 may be performed only after the clamping process, such that no internal pressure within the rigid housing 21 is present at atmospheric conditions. Therefore the rigid housing 21 is provided with the two holes 41a, 41b and the rigid housing 21 is clamped with only air inside, except for the at least one electric component 16. The rigid housing 21 may then be filled with the dielectric fluid 17 by using the holes 41a, 41b. A first hole 41a may be used for filling and a second hole 41b may be used for ventilation such that a vacuum during the filling process can be generated for ensuring a complete filling of the interior of the rigid housing 21. After the filling process the two holes 41a, 41b have to be hermetically closed, e.g. by brazing, soldering, or by using any other suitable technologies.

In more detail, filling the rigid housing 21 with the dielectric fluid 17 may comprise attaching filling tubes to the holes 41a, 41b; closing one of the tubes, opening one of the tube, and connecting the tubes to a vacuum pump;

evacuating the rigid housing 21 by means of the vacuum pump; opening one of the tubes for pumping, opening also the other of the tubes to let dielectric fluid 17 flow in; when fully filled, closing both tubes; detach the tubes;

optionally heating the arrangement 20 to cure the dielectric fluid 17; and closing the holes 41a, 41b hermetically.

In summary, according some of the herein disclosed embodiments there has been presented an arrangement 20 for subsea housing of electric components comprising at least some of the following features: A hermetic pressure- and liquid-tolerant power semiconductor housing is preferentially made of a ceramic or plastic material and thus suitable for subsea applications. A short metallic expansion joint may be provided on top of the ceramic or plastic housing. A base plate may be brazed to the ceramic or plastic housing. A semiconductor module lid may be welded to the metallic expansion joint to seal the housing hermetically. A flexible bus bar may be connection to the emitter contact plate of the power semiconductor. A silicone gel filling procedure that is based on using two holes may be applied. The spring constant in the metallic expansion joints and/or the springs may be tuned to make the hydrostatic pressure exchange most accurate.

The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

1. An arrangement (20) for subsea housing of electric components, comprising:

a rigid housing (21), the rigid housing being filled with a dielectric fluid (17);

at least one electric component (16), the at least one electric component being provided inside the rigid housing; and

wherein the rigid housing comprises pressure-volume means (22) arranged to enable a volume change of the rigid housing.

2. The arrangement (20) according to claim 1, wherein the pressure- volume means are expansion joints.

3. The arrangement (20) according to claim 1 or 2, wherein the rigid housing comprises a base plate (18), side walls (12), and a top plate (11), and wherein the pressure-volume means are provided between said bottom plate and said side walls or between said side walls and said top plate.

4. The arrangement (20) according to claim 3, wherein said top plate forms a lid to the at least one electric component.

5. The arrangement (20) according to claim 2 and 4, wherein said lid is welded to said expansion joint.

6. The arrangement (20) according to claim 3, wherein said at least one electric component is attached to said base plate of the rigid housing.

7. The arrangement (20) according to any one of the preceding claims, wherein the at least one electric component comprises a first electrical connector (16a) and a second electrical connector (16b).

8. The arrangement (20) according to claim 7, wherein said first electrical connector is an emitter contact plate, and wherein said second electrical connector is a collector contact plate.

9. The arrangement (20) according to claim 7 or 8, further comprising: a bus bar (31), the bus bar being provided outside the rigid housing and having a flexible portion (32), and wherein said flexible portion is electrically connected to said first electrical connector of the at least one electric component.

10. The arrangement (20) according to claim 2, further comprising:

a heat sink (35), the heat sink being provided outside the rigid housing and thermally connected to one of said top plate and said bottom plate.

11. The arrangement (20) according to any one of the preceding claims, further comprising:

at least one spring (24), said at least one spring being provided in the rigid housing and, wherein one of said at least one spring is arranged to extend between a respective one of said at least one electric component and said top plate of the rigid housing.

12. The arrangement (20) according to any one of the preceding claims, wherein the rigid housing is hermetically sealed.

13. The arrangement (20) according any one of the preceding claims, wherein the rigid housing is made of ceramic.

14. The arrangement (20) according to any one claims 1 to 12, wherein the rigid housing is made of plastic.

15. The arrangement (20) according to any one of the preceding claims, wherein the dielectric fluid is a silicon gel.

16. The arrangement (20) according to any one of the preceding claims, wherein each one of the at least one electric component is part of a semiconductor module.

17. The arrangement (20) according to any one of the preceding claims, wherein each one of the at least one electric component is part of an insulated-gate bipolar transistor (IGBT) power semiconductor element.

18. A method of manufacturing an arrangement (20) for subsea housing of electric components, the method comprising:

providing (S102) a rigid housing (21), wherein the rigid housing comprises pressure-volume means (22) arranged to enable a volume change of the rigid housing;

providing (S104) at least one electric component (16) inside the rigid housing; and

filling (S106) the rigid housing with a dielectric fluid (17).

19. The method according to claim 18, further comprising:

lowering (S108) the rigid housing into a body of water.

20. The method according to claim 19, wherein said body of water is an ocean or a lake.