Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Periodic Report Summary 1 - ALEA (Accelerated Life tests for Electric drives in Aircrafts)

Project Context and Objectives:
The concept behind the More Electric Aircraft (MEA) is the progressive electrification of on-board actuators and services. It is a way to reduce or eliminate the dependence on hydraulic, mechanical and the bleed air/pneumatic systems and pursue efficiency, reliability and maintainability.
Reliability in electronics is nowadays one of the most important subjects of study, as the range of its application is very wide.
At the moment, the lifetime problems of electromechanical actuators, adopted in MEA, have been addressed by analyzing separately the causes of failures, and accelerated tests were proposed for the single components. This project aims at realizing a test bed able to apply multiple age accelerating stresses and to realize the on-line test of the electric machine and drive, under different operating conditions.
The main failure in electric drives is due to electric faults resulting from the damage in the motor winding insulation system. In this work the main stress factors affecting the lifespan of insulation materials in aerospace applications will be analyzed. A special test rig will be also proposed, to assess insulation lifespan modelling under various stress conditions, especially investigating the interaction between ageing factors. The test rig will allow to characterize insulation degradation under variable ambient and power supply parameters for simple models, such as twisted pairs, up to coil form and complete machine operated at rated load. The results of the work that will be carried out will allow to identify the most influential factors affecting insulation lifetime and the interactions between them.
The test rig comprises a Thermal vacuum chamber, an embedded dynamometer/brake system and a custom inverter based on SiC devices capable to apply PWM commutation of different dv/dt ratio.
The test rig will embed an environmental chamber able to replicate the ambient conditions at 50000ft, moreover, a custom converter able to vary the voltage stress at the motor’s terminal will be developed, in order to test the reliability of the motor with the converters of the future, that will employ always faster devices.
The test rig would allow an all-in-one approach for multi-parameter measurement, thus minimizing the required test runs.
The test set-up will thus provide a means to confirm, experimentally validate, and also fine-tune insulation degradation lifetime models. In particular a lifetime model, based on the physic Of Failure (PoF) method, that considers the impact of the different stress factors on the system, is expected to be developed during the project.
The ultimate goal is to foster the development and adoption of electric drives for aerospace applications, resulting from more reliable procedures that allow accurate estimation of a system lifetime from the design stage (design reliability work flow).

Project Results:
The work performed since the beginning of the project is related to WP 1 to WP 7 and WP 14, as detailed in the following sections:
WP1 - A detailed literature review of the electric drive systems for aerospace applications was performed with particular attention to reliability study of the electric machines failure mechanisms, and the proper accelerated test procedures. At the same time a review of the diagnostic/prognostic techniques that gives an indication of the life consumption of the electric drive system was performed.
WP2 - The test bench brake and DAQ systems were defined. After the preliminary design study, the components needed to realize the system were defined, according to the parameters and specifications for the electrical, thermal and mechanical quantities to be monitored, together with the sampling rates and acquisition policies agreed with the Topic Manager. For the sake of test rig flexibility, sensible overload margins were considered.
WP3- The MUT converter components and architecture were drafted, in order to meet the general specifications of the MUT drive given in the call for proposal and discussed with the Topic Manager. The appropriate drive system (component devices, architecture) has been selected be selected, together with the interface and safety requirements for the MUT inverter.
WP4 - After the preliminary design study, the components needed to realize the system were investigated, according to the specifications decided in the negotiation process.
The vacuum thermal chamber features a custom high speed seal for the MUT shaft that allows to change the MUT in a fast way while guaranteeing the thermal insulation and the airtight seal for the other components housed outside of the test chamber. Several Thermal Vacuum chamber manufacturers were contacted to assess the feasibility of the required customizations and to identify a standardized set of mating ports to interface with the rest of the test rig components.
WP5 - The complete test bench for the motor under test (MUT) was be designed after the relative standardized mating ports with the Thermal Vacuum Chamber were identified: suitable shaft seals were employed to allow the installation of the motor under test inside the chamber, while keeping the rest of the equipment outside at ambient pressure and temperature. Test bench brake/dynamometer and converter were selected, together with the required transducers (torque meter, accelerometers, etc...). Airtight feed-trough for transducers and power supply to MUT were designed to allow experimental setup flexibility
WP6 - The power converter supplying the Motor Under Test was designed and a selection of the power devices employed was performed. SiC Mosfet was selected as power modules, as up to now they represent the more mature implementation of wide-bandgap semiconductors, and several manufacturers are selling discrete devices or power modules.
A programmable gate driver able to select different resistors (corresponding to different calibration of the dv/dt) was designed. Special care was taken to guarantee the protection from destructive events, i.e. loss of gate driver signal, spurious turn-on, overheating and overcurrent.
WP7 - In this WP the work of WP5 and WP6 were thoroughly reviewed by the partners, the designs underwent a search for weak points, and the risks associated with each choice was analysed, and appropriate design/architecture modifications or countermeasures was taken to minimize these risks.
The final validation and critical design review was carried out together with the Topic Manager.
WP14 – A detailed literature review of existing lifetime prediction models for electric drives, mainly focused on the electrical insulation of the motor windings, was performed. The possibility to realize a complete lifetime degradation model of an electrical drive was investigated according to the specifications identified in WP1.

Potential Impact:
ALEA project aims at achieving complete and accurate life time models for electrical drives and the realisation of a test bed that is able to validate these models by applying multiple age accelerating stresses and to realize the on-line tests of the machine drive under different operating conditions.
Regarding the short-term impacts, the initial technology review will thoroughly analyse the state of the art regarding lifetime models and reliability of drives. Such studies, which today have never been conducted in too much detail or applied to generic life models (applicable for a wide range of electrical machines) represent a considerable improvement in terms of progress beyond the state of the art. Designers and manufacturers of electrical machines would benefit greatly from such models.
The results from this investigation are predicted to give also a higher level understanding of these phenomena and will also result in the current design, manufacturing and assembly procedures to be improved.
The main output in terms of lifetime modelling of electrical drives will be the creation of an accurate combined life model. This will result in considerable improvement on the understanding of the mechanisms of failures of electrical drives. This is projected to have a huge impact on the design of electrical drives. The application of comprehensive lifetime model to the design procedures of electrical drives will improve reliability of electrical drives, which for the aerospace sector has always been a main limiting factor.
In fact, this project will enable highly improved design methodologies that will reduce the risk of insulation degradation. One expected outcome will be the improvement of geometrical positioning of impregnation compounds in order to reduce insulation degradation including degradation due to PDs. The project will also have impact on the industrial process for realizing motors. As a matter a fact, the capability of motors to avoid PD effects is greatly affected by the industrial process of automated winding. Such improvements in reliability will result in a considerable help for European motor and drive manufacturers to improve their products and thus become more competitive world-wide.
Having more reliable and higher performing motor drives could aid European institutions in the race against the ever-increasing Asian market.
The procedures to realize the test bed, the data acquisition software and the post-processing software that will be developed during the project will be helpful to further push the limits of testing of electrical drives. Moreover, the test of actual motors and the data acquired will constitute a database that will improve the existing knowledge of life time models.
The ability to modify the actual voltage waveform characteristics of the converter driving the motor under test, in conjunction with the other test facilities, constitutes a great improvement on the existing testing methodology, that usually imply off-line accelerated testing of the twisted pairs. The ability of the test set-up to look at different technologies of motors is also an asset that will improve the understanding of failure mechanisms related to specific motor technologies.
The long-term impacts of the project are related to the new power devices that are being researched and tested by the inverters’ manufacturers. In fact, the constant pursuit of the maximum efficiency and power density, in addition to the increasing requirements of the control system, have forced the designer to increase the power devices’ switching frequencies. In this framework, the machines are subjected to extremely high voltage stresses, whose effects in real operating conditions have not been assessed yet. As a matter of fact, the impact of the work from this proposal will be critical for motor manufacturers that can optimize their design workflow depending on the expected lifetime of the machine.


Stefano Selleri, (Head of Department of Information Engineering, FSIGN)
Tel.: +39 0521 905763
Fax: +39 0521 905758
Datensatznummer: 183998 / Zuletzt geändert am: 2016-06-09
Informationsquelle: SESAM