New challenges for the Active and Isolated Rectifier Units (High performance TRUs) to support the MEA concept are demanding deep changes compared with the conventional TRUs. INDRA and CEI-UPM, the consortium that is presenting this proposal, has a wide experience in the area of high performance TRUs for the new aircraft requirements
The basic architecture that allows for these high performance TRUs has three stages:
- EMI filter to meet the EMI standards;
- Active Three-Phase rectifier to control the demanded sinusoidal current (THD and PFC) as well as control the output dc voltage (VBUS DC);
- Isolated dc/dc converter that provides galvanic isolation, adapts the voltage and power to the specifications (28V) and it can be in charged of some control capabilities (battery charge mode, voltage source mode, current source mode, some protections).
Within this project, this basic architecture will be considered and compared with the multiphase solution (several converters shifted and operating in parallel) as well as some active and isolated rectifiers proposed in the state of the art. For the isolated dc/dc stage, advanced topology solutions with soft transitions will be analysed since they allow to operate at higher frequencies, reducing the weight of the final unit. A topology recently proposed by UPM-CEI  is really appropriate for this application since it presents almost zero switching losses.
A review of the state of the art has been done and the consortium is proposing to meet about 1.5kW/kg for the whole EMI + AC/DC + isolated DC/DC. This objective is based on the experience in a previous project, and it is a goal beyond of the state of the art (about +20% or +25% higher power/weight ratio). It is doable thanks to the use of high frequencies combined with soft switching techniques. Besides, the use of new SiC and GaN semiconductors will be analysed and considered in the design since they allow for higher temperature operation as well as higher frequencies.
Final Report Summary - AIR (Active and Isolated Rectifier unit for more electric aircraft: Design and Manufacturing of a 10KW AC-DC Converter Unit (AIR))
As the periodic scientific reports have been done in a historic and summary way, the complete executive summary of the project is equivalent to the final period-3 scientific report.
So, please check this document to see complete details of project execution, objectives, results, deliverables, milestones, dissemination, coordination and management and use of resources.
Project Context and Objectives:
This project was proposed in three main phases:
- Initial details matching analysis between power AC/DC converter in passive topologies (transformer-rectifier) and AC/DC regulated converter based in previous and new topologies. This study shows in a first step the benefits of use converter regulated vs. passive ones. Even with enhanced input transformer design the passive AC/DC's (or TRUs) have important limitations in the power quality, especially in input distortion, output ripple and output voltage stability as function of the input voltage and output load. Although the passive topologies have the advantages of their maturity, robustness, simplicity and competitive power/volume-weight ratio, the new topologies show a drastic improvement in the power quality parameters and a challenge in the volume and weight target, especially when the objective is to achieve the same level of robustness and safety than in a passive and non-regulated converter (TRU). This aspect is more important when the advance through a "More Electrical Aircraft" is more and more necessary, requesting more power and making more and more important the quality of the electrical parameters due to the increase of the limitations between power sources and electrical loads and requirements of the loads, especially when in this scope, the use of COTS products as loads is trying to introduce at high scale.
Thinking in this approach through the aeronautical future and linked to the R&T nature of this project, the second step of this analysis was focusing on the selection of the best AC/DC active topology as substitute of traditional ones, getting the best electrical behaviour, keeping the same performances in robustness and safety requirements and allowing to be as close as possible in the target of weight and volume requirements.
After a long analysis and several loop of rework, two main topologies were preselected (Buck rectifier + Full bridge and Vienna rectifier + Full bridge).
- Detail design of an AC/DC regulated converter.
Preliminary design and details simulations of both topologies was done to analyse all the steady stat, transients, and fault cases in both preselected topologies. Moreover, predesign of magnetic components was done to take into account main volume and weight of the topologies for the final matching and selection. So, due to bidirectional aspects, fail-safe behaviour up to with double high failures, number of components and expected weight/dimensions, the Buck rectifier topology+Full bridge was selected. This topology is the safest against aeronautical requirements and with a good robustness level and allowing output voltage regulation and input distortion control.
Following this, a detail design and a manufacturing dossier was done.
- Manufacturing and tests of the AC/DC regulated converter prototype.
In this final phase, several activities were done in parallel, such as manufacturing of some components as PCBs and magnetic components, mechanical parts, control and SW and preparation of the laboratory. After testing phase was done step by step, from subassembly debugging and tests, main stages in open and close loop tests, power stages and control integration and final testing at converter level.
Although the weight/volume was higher than initially expected, part of this was due to the mechanical design used, to allow more visibility and operability over this prototype. Also, additional design margin was included to limit the risks of a complete testing. So, the final design and testing have confirmed a good behaviour and a margin to improve in the weight/volume for a future redesign more integrated and with higher TRL. But relating to power capability, efficiency, and electrical performances the current design has showed a big competiveness of the selected topology and design. And due to this, Indra will continue working over this design thinking in a future product.
Although the use of an AC/DC Buck rectifier topology combined with a DC/DC full bridge otology is already used in the industry, this one has not been used, to our knowledge, for power converters of 10-20kW with critical safety requirements in aeronautical environment. Moreover, in the prototype has been included last generation power components and customized design of magnetics.
For the controls part, also last advantages in PLL control have been included and customized to achieve a highly efficient power input for reducing input distortion.
Although the design has been done taking into account air cooling, future liquid cooling could reduce even more the weight and dimensions.
And of course, the main results of the project are the validation of the design through the physical manufacturing of the prototype and its tests result at complete equipment level.
Linked to the satisfactory results obtained from this project, it is expected to continue in three working lines:
- PhD line focus in the AC/DC control used in this project and future enhancement.
- Development of a new AC/DC prototype with bigger TRL, optimized weight/volume and including materials and process in accordance with aeronautical standards.
- Develop two new designs and prototypes derivate of this topology and in the same power range, by updating the power input and power output to other electrical aeronautical standards (i.e. power input from 230Vac to 115vac and power output from 28Vdc to 270Vdc).
Associated to these new working lines, direct workload will be immediately generated. But the final idea is to achieve introduction of these new products in the current aircrafts and also in future ones. The inspection over some commercial opportunities have been initiated and derivate of this, the process of redesign, qualification and certification could be accelerated. And if these objectives are achieved in the closer future, additional workload associated to serial production will be generated in Europe, where Indra has installed all its production facilities.
And thinking in the future maturity of these designs and future certification and introduction in legacy and future aircrafts, this technology will contribute to the objectives of the Clean Sky programs for the development of a "More Electrical Aircraft" that is aligned with main objectives of fuel, COx/NOx emission and noise reduction.
To note that in parallel to the redesign, commercial and industrial activities, additional activities of disseminations will be done by the University and by Indra. Although the present design is not patented but protected by IPRs over the concrete and critical design, general aspect over the benefits of this technology will be transmitted to the scientific forum for getting synergies in other fields of application. Benefits of the European projects and results will also be presented to the general public (especially in secondary schools) to motivate youths to continue with studies and increase the joint and collaboration European Spirit.
List of Websites:
In addition to the initial and concrete websites generated for this project in both entities (Indra and UPM), a dedicated website for the project was generated and it has been kept up to date. This website showed things like technical information (scope of the work, summary of the activities done, and results obtained, including figures) and management information (news, meeting and dissemination events) and the contact point for more information.
This website is:
and the focal point is Luis Verdugo (PM): email@example.com
More details of website information have been included in the "PUBLISHABLE SUMMARY REPORT.pdf" file.