Electrical machines and drives being developed within the Clean Sky programme are adopting novel, power-dense, circuit and electromagnetic topologies working close to the material limits and excited by non-conventional waveforms. This brings about requirements for increased health-monitoring and cooling demands for both motor and convertor and thus temperature and vibration monitoring are fundamental. This translates in an increase in temperature sensing requirements for correct thermal management and therefore added component count. With motor-drives going at high speeds and high frequency there are challenges for data acquisition and challenges for determining the rotor speed using resolvers. The use of such conventional sensors, for both temperature and position/speed measurements pose a significant reliability overhead.
Over the past years optical fibre sensors based on Bragg gratings have been developed for quasi-distributed temperature and strain/vibration measurements. This project therefore aimed to explore the possibility of using such technology as a replacement to conventional bulky systems prone to EMI issues whilst at the same time provide a test platform which will provide the necessary feedback on the axial the circumferential distribution of key parameters such as temperature and strain. The same applies in terms of power electronic convertors for heat sink design validation and online device temperature monitoring. Thus, the development of such a SMART self-monitoring motor drive provides a method for enhanced reliability and time-to-failure prediction.
The purpose of this project was to develop a test setup able to investigate the integration of In-fibre gratings within the electrical drive components including the machine itself and associated power electronics. Work will be done to extract temperature and strain data, this data will in turn be fed-back into lifetime models used to predict/monitor the drive’s operating conditions.
The electrical machines and drives being developed within the Clean Sky programme are adopting novel, power-dense, circuit and electromagnetic topologies working close to the material limits and excited by non-conventional waveforms. This holistic design of motor/load/power converter aims to maximize the system efficiency and minimize system weight. It is therefore desirable to equip the electrical system with advanced diagnosis and prognosis, coupled with advanced thermal management, thus, to offer improved efficiency and enhanced reliability. The conventional sensors, however, have shown limitations in terms of the insulation required for working in harsh environment with high EM interference (EMI), added weight and difficulty in coping with the space constraints and in determining the rotor speed/position when the electric machine operates with high speeds and high frequency.
This OFS-MOTOR project has demonstrated successfully an optical fibre based self-monitoring motor drive which is integrated with a novel all-in-one optical fibre sensor system, developed using a generic fibre Bragg grating (FBG) sensing platform. This is achieved by integrating four fibres, each carrying 12 sensing points (FBGs) fabricated using a laser technique, respectively into the motor stator and rotor for simultaneous measurement of a number of key parameters. This includes the real-time measurement of temperature distribution of the stator and rotor, vibration, torque, rotational speed and rotational position and the sensor data obtained enable subsequent fault diagnosis, hot-spot identification and energy efficiency analysis and preparation for next-stage integration into the motor control software.
The test bed developed includes the SMART motor drive under test, load motor and its control, together with the conventional sensors and their data logging systems. The sensor data generated from the all-in-one optical fibre sensor system have been successfully validated against the conventional sensors, confirming that the FBG technique has shown to be a promising replacement to conventional bulky systems prone to EMI issues. Such innovative test bed is now at the Topic Manager’s institution and made available to the EU aerospace industry for access to test various types of aerospace motor drives under the circumstances as the machine used in real world.
The success of this pilot project has further confirmed the effectiveness of using a transformative approach by switching sensing mechanism from electrical to optical domain, taking full advantages of the latter being insensitive to EM interference, small size and capable of multiplexing a number of sensing points within a single length of fibre, a key feature resident in the advanced FBG technique being explored.