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Power Conversion Units for LifeRCraft demonstrator

Periodic Reporting for period 3 - POCOL (Power Conversion Units for LifeRCraft demonstrator)

Reporting period: 2018-12-14 to 2019-06-13

Our project (POCOL - POwer COnversion units for LifeRcraft) takes place in the frame of CleanSky 2 for the Airbus Helicopters LifeRCraft helicopter program. In this context, two leading institutions in the field of power electronics, Techniques et Fabrications Electroniques (TFE) and the University of Nottingham (UNOTT) are combining their forces in order to enable a step change in the development of high specification power converters for modern aircraft application such as for the LifeRCraft helicopter.

Overall objectives:
Within POCOL, TFE and UNOTT work together to:
• Develop models and design the required power converter to meet the functional and operational performance and reliability requirements set out in the technical requirements documents using the technical expertise of the two partners.
• Manufacture B1 prototypes that meet the design criteria up to TRL5
• Test the B1 demonstrators under relevant environmental and operational conditions
• Re-iterate the design process to include improvements in performance and reliability informed by knowledge gained from B1 model testing into updated B2 models
• Build B2 demonstrators and test and validate up to TRL6 as part of the LifeRCraft programme
• Provide relevant documentation to prove required certification and extrapolation to full production

The questions concerning the issues being addressed and the importance in society is answered in the technical report (too long to be written here).
The list below provides a status by work package for POCOL project

WP1 - Management - KOM held 21st Dec 2015; Project coordination & management on going.
WP2 - Product Description - Completed. First releases of required documents were produced by UNOTT and TFE.
WP3 - Preliminary Design - Completed. This preliminary design activity were achieved mainly by UNOTT and resulted in a mock up manufacturing and validation test activities. At the end of this phase (Feb 2017), conclusions from industrial partners (namely TFE) with the support of end user (AH) stated the academic optimal topology for DC-DC bidirectional converter proposed by UNOTT was not the best choice when all implementation and industrial constraints are evaluated.
WP4 - Critical Design - BeginninCompleted. Because of the conclusions of previous phase, an updated preliminary design activity had to be performed, led by TFE, including: architecture choice updating, design analysis, simulation activities including control stage design. Then a 3D CAD model was produced. An updated PDR occurred leading to a reject status, mainly because of weight and dimensions issues. A design optimization was conducted, focused on cooling optimization, volume and weight savings. In parallel, safety and reliability aspects were analysed and included in design requirements. A CDR was conducted in two phases : first phase in June 2018 in order to launch B1 manufacturing. Second phase in November 2018 to review all documentation linked to this milestone. All documents are up to date. CDR activity is closed
WP5 - B1 models - Completed. First power sub-assembly has been tested in both Buck and Boost mode, in open loop. The only weakness detected is the overheating of the power transformer. This power transformer will be improved for B2 model. A temperature sensor near the transformer has been added on first model in order to avoid damage due to this over-heating phenomenon. This model was delivered to AIRBUS after a Prototype Inspection in July 2019.
WP6 - TRL5 maturity testing - Started. Functional validation and verification versus specification was performed including thermal validation. EMC derisk was also performed
WP7 - AH Integration tests - Started. Model B1 has been delivered. Buck mode has been tested on Airbus test bench.
WP8 - Critical Design update - Completed. Main modification was the redesign of the power transformer for which a new design, fully proprietary, were studied. The purpose of this transformer was to reduce losses to improve thermal behavior using a planar technology
WP9 - B2 models - Started. Testing activity started with the new power transformer showing a 20°C improvement in temperature behavior, then a first power module was assembled and tested confirming the good results and non regression on other parameters. B2 model was fully assembled and tested.
WP10 - Flight clearance testing - Started with the test of firmware of complex component (FPGA). Equipment test procedure and associated report were released. The qualification test plan applicable for flight clearance has been agreed with AIRBUS.
The present progress of the project is yet able to confirm that the following research areas are addressed:
• Use of silicon carbide (SiC) semiconductors on high voltage side.
• Parallel association of switching cells organised around highly integrated magnetic devices.
• Higher switching frequencies. Optimization takes into account the reduction of allowed emission limits with the increase of the frequency and that high band gap components are generating very high level of common mode parasitic switching current.
• Operating safety with high level of operational availability as a design target. A failure mode and effect analysis will be performed during the conceptual phase to ensure converter architectures allow privileged operational degraded mode (mission continuity).
• Smart air-cooling is at the heart of the integration study as the compact specified outline does not allow multiple air flow exchanges and make internal thermal exchanges limited. The use of high temperature components help for that.

The impact of this project so far can also be assessed as a proven advantage for TFE company on its market. Since its beginning, TFE has been committed to the development and supply of power conversion solutions for aerospace stakeholders. Thus, TFE has continuously been active in R&D projects allowing experimenting and mastering of state of the art, power electronics technologies applicable to the aerospace industry. These include high frequency switching, digital control and algorithm development, software and firmware development and certification, numerical simulation etc…

Thus, in order to maintain its present position as a leading supplier of power conversion solutions for aircraft, TFE must be able to propose to its customer’s mature and proven alternative solutions to the soon-obsolete transformer-based solutions (HVAC to LVDC). This indicates advanced converters technologies (HVDC to LVDC). A project such as POCOL falls directly into TFE’s technological strategy and will be a step forward towards this objective. This anticipated story has now started and POCOL allows TFE to get closer to the helicopter business.

For TFE, this project allows to maintain and reinforce (with new competencies) a team of engineers and technicians in the R&D department, which is an important part of the headcount of the company. In a short term perspective, the industrial nature of this product will help the growth and development of the company while creating the jobs necessary to fulfill its task. On a long term basis, the objective is to have a manufacturing area and team dedicated to this activity. The number of jobs available will go increasingly as the activity grows.
Test board current capability @ 100kHz
Dimensions 162x100mm, Measurement board designed