Towards the Holy Grail? A Novel, Power Dense, Low Noise Permanent Magnet Motor

Abstract

High power, high efficiency propulsion equipment with a high shock resilience capability that occupies the minimum volume, with a low weight and a very low noise signature is a “holy grail” of naval propulsion. Significant steps towards this goal have been made in the area of naval electric propulsion in the last 30 years, but it is hard to combine all these features in a single design since some features tend to militate against others. Solutions, therefore, require a balance between the thermal challenges of high power in a low volume and the requirement for shock proof, low signature machines. A permanent magnet propulsion motor with a patented novel cooling system designed for power density and low structureborne noise is being developed, manufactured and tested as a technology demonstrator. It is part of a programme part funded by InnovateUK under the Optimised Electric System Architecture project in partnership with the University of Nottingham and the University of Warwick. The primary market for the motor is envisaged to be naval and marine research vessels where power density and low noise is important. The motor is low speed and designed for direct mechanical coupling in the shaft line to the propeller and will be suitable for full electric or hybrid propulsion since the design is inherently scalable from relatively low powers up to those required for full electric warship propulsion. This paper describes the principles of the design and the approaches used to achieve the combination of high power density, high efficiency, high torque and low noise. It describes the thermal management approach and how the thermal behaviour of the different elements of the motor have been modelled. It also shows how advanced modelling techniques, combined with laboratory based and simple, practical testing have been used to develop the design and the manufacturing techniques required by this innovative solution. The paper also describes the testing approach used to validate the machine and its integration into a wider Direct Current or Alternating Current distribution system that could include energy storage elements. Finally, the performance of the motor is discussed along with the probable next stages in its development.