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Autonomous Wireless Current Sensor for Aircraft Power Lines

Periodic Reporting for period 1 - AMPWISE (Autonomous Wireless Current Sensor for Aircraft Power Lines)

Reporting period: 2018-02-01 to 2019-07-31

The objective of the project is to develop an energy autonomous wireless smart and low-cost current sensor for monitoring of electric lines in the context of the coming generation of aircrafts.

The project addresses weight reduction directly by removing the need for communication cables (wireless communications) and indirectly by supporting new electric power distribution topologies resulting from migrating to electric actuation. A secure, smart, low-cost and possibly compact autonomous current sensor will allow to measure at places that not accessible. To this aim, the consortium will develop and integrate the following components:
- A sensor architecture that balances the possible energy supply (through scavenging) with the consumption sources, sensors and electronics, in particular for communications, while meeting the temporal requirements in terms of latency and sampling frequency,
- The sensing, processing and power management electronics,
- An energy scavenger including its power conversion electronics,
- A current sensor based on an existing product adapting within possible limits its form factor to the topic manager requirements
- The wireless communication electronics in the 4.2-4.4 GHz band,
- A protocol exploiting above electronics and able to support secure, low-power and time-bounded communications in presence of interferences and coexisting networks,
Laying out the system architecture was the objective of Work Package 1. The requirements were submitted by the topic manager Safran Electrical & Power (Safran E&P) and analysed by the consortium. The overall system architecture, including wireless networking aspects, data acquisition and processing, hardware, current sensor and power supply and balance was presented in project deliverable D1.1 “Global Solution Specifications”. It also included a list of qualification tests.
The power consumption estimate resulted in an average power consumption below 1.5 mW given a 5 minutes current sensing period, which matches the energy harvesting potential estimated at 2 mW using an inductive energy scavenger, if the average AC current in the bus bar is over 3A. This figure is a starting point and it will be revised during the on-going sub-system development, with new current estimates coming from Safran E&P.

The processing and communication electronics was based on the MSP430 microcontroller from Texas Instruments and on the AT86RF233 radio from Atmel and initially presented in D1.1. During the still on-going WP2 – Wireless Communications, it was decided to move to the Nordic Semiconductor SoC NRF52840, as reported in D2.1. This more modern design allows to further reduce the power consumption and the form factor as well to benefit from the ARM Cortex MCU to drive the current sensor which design progresses in parallel and shows that it needs fast ADCs and significant data processing power.

The power management advances so far include the design of a novel power management system, including supercapacitor storage. The corresponding PCB fabrication is underway and testing along with a 2nd version of the energy harvesting transducer, which is also being fabricated is scheduled for the following few months.

Two novel harvesting prototypes have been developed, one thermoelectric and one inductive. The two prototypes have been tested, and the inductive approach has been selected as the most suitable. The final inductive energy harvesting prototype is being fabricated and a novel power management system including storage has been developed. The PCB fabrication is underway and the complete power supply is due for internal testing within the next few months.

Partner SENIS has already done two iterations on the Hall effect electrical current sensor. The latest version was sent to CSEM for interfacing with the microcontroller. The circuit can measure currents as low as 0.5 A and consumes only 7 mA when in operation, which is a remarkable result.

Partner CSEM built a demonstrator of a WAIC band 4.2-4.4 GHz transceiver using a frequency shifter coupled with an Atmel AT86RF231 radio compliant with IEEE802.15.4. The tests reported in deliverable D2.1 show that the demonstrator exhibits a packet success rate about 5% better than the radio operating without the frequency shifter. This is probably due to the higher interferences in the 2.4 GHz band. The drawback of the demonstrator is that it is bulky, and because it is not possible to miniaturise it within the project limited resources, the topic manager Safran E&P advised to focus on an optimal and well integrated sensor node prototype operating in the 2.4 GHz ISM band. CSEM also developed and measured antennas for both the 4.3 and 2.4 GHz band. The current sensing application needs were established and its duty cycle determined with the topic manager help. The application layer protocol was dimensioned and described in D1.1.
The AMPWISE project will advance over the state of art along the following 3 axes:

Energy harvesting
- state of the art: power line harvesting proof-of-concept demonstrated
- AMPWISE progress: broadband power-line harvesting from the return current structure in aircrafts. Power supply with management and storage for reliable energy autonomy

Current sensors:
- state of the art: current transformer, Rogowski Coil and through voltage measurement on a resistor.
- AMPWISE progress: open-loop, Hall-based current sensor with a slotted ferromagnetic ring. Optimised for energy consumption. Embedded data processing.

Wireless communications:
- state of the art: adaptive TDMA, coexistence and robustness based on channel hopping, security based on pre-distribution of keys
- AMPWISE progress: WAIC band demonstrator, dedicated optimal antennas and integration of the different aspects in a single solution with optimal duty cycle adapted to both the 4.2-4.4GHz and 2.4 GHz bands.

The programme of which AMPWISE takes part (Clean Sky 2) aims at further reducing energy consumption and pollution emissions. Compared to 2014, the objective is to cut by 30% fuel burned and CO2 emission and by 40% NOx emissions and noise by 75% before 2035. Weight reduction is a key objective and leads to an increase of electric equipment in particular for the taxying phase. All this results in the need for current sensors that can be installed at various locations in the aircraft including locations where wiring is not possible. The use of wireless sensors, contributes to the reduction of wiring for power and data transmission, the containment of weight increase and the reduction of electrical wiring complexity. The possibility to embed autonomous sensor in aircraft will offer considerable possibilities for the aeronautical domain. The project will allow simplification of cabling structure and weight, because of the energy autonomy and wireless features of the monitoring system. This is directly in line with the Clean Sky 2 programme. Furthermore, the project will deliver the first miniature energy-autonomous sensor at this level of maturity under the aircraft industrialization standard.

Another positive impact is the increased safety as the autonomous sensors are developed to be installed on the structural elements which are also used to carry the return current. The sensors will allow the assessment of the current flow effect on the structural elements and the detection of potential problems.