Objective:

”Establish fundamental competence on new and pioneering concepts for realizing power electronic converters for deepwater applications. The developed know-how will give Norwegian vendors and oil companies new possibilities for realizing future challenging oil and gas projects”

Sub goals:

1. Provide a review of the major weaknesses and uncertainties of the today's concepts for high power converters for deepwater applications.
2. Clarify the operability of pressurized (200 bar) power circuit and driver circuit components through cooperation with manufacturers and by testing components in laboratory.
3. Demonstrate possible new design solutions by use of pressurized power circuits and transistor driver circuits
4. Provide methodologies and guidelines for qualified pressurized converter designs, including support for upgrading of specifications
5. Accomplish a PhD degree within liquid dielectrica for pressurized power electronics

Benefits by exposing power circuit to ambient pressure

• Weight and volume of pressure chamber significantly reduced
• Electric power penetrators significantly reduced due to reduced numbers of connections between pressure compensated and 1 bar chambers
• Enables less complex and more reliable cooling system (e.g. direct conductive cooling, eliminating pumps, heat exchanger etc.)
• Reduced cost for subsea VSD A design which take advantages of the benefits listed above will be simpler and reduce the costs for subsea VSD
• Increased reliability A simpler design with less components will probably result in higher reliability.

Industrial relevance

• Future oil and gas development projects call for reliable power electronics:
  - Small and medium power (0.1-100 kW) supplies for electronics, actuators etc.
  - High power converters (0.1-100MW) for variable speed drives.
• Ongoing projects, e.g. Ormen Lange, have revealed that frequency converter is the Achilles' heel when it comes to obtaining reliable and feasible solutions.
  - The challenges are related to obtaining satisfactory reliability figures and obtaining manageable size, weight and costs. 
• One goal for this project is to prove that critical components can operate with satisfactory reliability in high pressure environment
  - This will open up for the realization of quite new concepts for realizing more manageable converters, also including more confidence when it comes to reliability
• The results from the project will be accessible for the supplier industry joining the project.
  - Especially will the results from the work-package be available for manufacturers of power electronic converters joining the project

Progress plan and milestones

Cost allocation and financing scheme (1€ = 8NOK)

*) NTNU contribution is in kind (supervision of Ph D student and 1 year scolarship to Ph D student).

Task descriptions

Task 1:  Review of the today's concepts
The objective of this activity is to clarify the major weaknesses and uncertainties of existing and proposed converter concepts for deepwater applications. To the extent information can be released, the project team at SINTEF Energy Research will utilize information and experience from projects on evaluation of concepts proposed for subsea projects like Ormen Lange and others. A review report summarizing major weaknesses and prospective improvements will be issued. The report will also contain base guidelines for the focus in the subsequent activities

Task 2:  Identify critical components
A review of actual power circuit topologies will form the basis for identifying components needed for realizing a pressure tolerant power circuit. The candidates are the components normally constituting converter power circuits such as power semiconductors and capacitors, essential additional components such as gate drivers including power supply, sensors and cooling circuits. The review will not highlight special topologies or compare topologies, but aim to focus on components required to form building blocks for several types of topologies in a broad power range. This task also assumes a good dialog with participating converter manufacturers. A summary report with candidates subject to investigations will be worked out.

Task 3:  Feasible technologies for pressurizing
A thorough feasibility study of power circuit components will be accomplished one by one. For each component there might be several alternative technologies. (E.g. the DC capacitors could either be film type ore electrolytic type.) Dialogue with the manufacturer's own expertise as well as involvement from SINTEF's own material experts will be important in this phase of the project. Components constituting driver electronics will mainly be managed by SINTEF ICT. A literature study, also including open results from related international research programs will be included.  A report will be worked out, containing identified components, feasibility for pressurization and plans for required special tests. The results from the report will be input for task 5. The plan for special tests will also contain needs for special laboratory equipment. Results from study of gate driver component study will be input to task 4

Task 4: Pressurized gate drivers
Results form the feasibility investigations of gate driver component in task 3 will be input to idea-shaping for simple and robust gate driver systems including power supplies. Here SINTEF's own experience from gate driver development is expected to become very useful. The most promising concepts will be realized as prototypes and prepared for pressure testing in task 5. A report will be worked out including circuit diagrams for the proposed designs, results from one bar testing, and plans for pressure testing.

Task 5:  Laboratory pressure testing of components
This is undoubtedly the most extensive activity of the project. The most promising components will be tested under specified pressure (e.g. 200 bar) in the laboratories at SINTEF Research. The test bench will be designed for enabling electrical tests on pressurized objects. Under the tests electrical parameters will be measured to monitor any changes due to long time effects. Accelerated aging tests, e.g. by increasing the ambient temperature and/or pressure cycling, will be considered. After finished test period the test object will be investigated by electrical measurements and visual inspections to uncover any effects of long time exposure to high pressure.

Task 6: Demonstration of pressurized power circuit
This task aims to realize and pressure test a converter power circuit under pressure. This circuit will represent a building block of a converter including all components investigated in the preceding tasks. An obvious circuit candidate is a bridge arm of a two-level converter, constituting upper and lower IGBT, DC-link capacitor bank, possible snubber circuits, gate drivers, output power filter and essential parts of the cooling circuit. A test report will be worked out, including test results prospects for improved converter designs with reference to the assumed advantages.     .

Task 7:  Methodologies and guidelines
Findings and conclusions from the preceding activities will form the basis for preparation of methodologies and guidelines for qualified pressurized converter designs. It is also the intention that this report will give valuable support for upgrading of existing component and converter designs

Task 8:  PhD scholarship
The PhD student will focus on subjects within liquid dielectrica for pressurized power electronics He will enter the project team and be fully integrated in the project

Power electronics reliability issues

Converter vital components

Challenges to reliable converter design (Picture showing 100 kW (17 kg) frequency converter developed by SINTEF)

Status from the  self-financed SINTEF project: Power electronics for extreme subsea and downhole ambient conditions�0;0;B;

Ongoing research activities

• Literature survey indicates that not much have been done world wide on developing pressure tolerant power electronic devices.
• SINTEF ICT have an activity on pressure tolerant electronics
• SINTEF Energy Research have an activity on pressure tolerant power electronics
• Capacitor manufacturers offer capacitors for pressurizing (Ormen Lange)

Commercial products

• Products with pressurized power electronics for seismic application is realized
• As to our knowledge there are no solution for sub sea power supply based on pressurized power electronic available.

Ongoing test of IGBT module in silicone oil pressurized to 200 bar – Started October 2005

• For the time being switching 300 V and 150 A
• No change in operational performance, or �0;0;B;negative effects from high pressure has been�0;0;B;observed so far
• Long time effects not known at the moment.
• Test to be extended with other power components�0;0;B;and electronics