Transverse flux motors for electric propulsion of ships

Electric propulsion is steadily becoming an established technology for many types of commercial ship including passenger liners, ferries and coastal icebreakers. Major advantages of electric propulsion include low noise, reduced operating cost, increased flexibility of operation and improved naval architecture. Future generations of naval surface ships will be propelled by directly coupled electric motors at around 20 MW 200 rpm per shaft. The naval application is a very challenging one, requiring an efficient motor, with high volumetric power and torque density, high reliability and durability. Permanent magnet motors offer a number of benefits for this application and many of the world's navies are now looking to introduce electric propulsion technology using one or other form of permanent magnet synchronous motor driven from a PWM voltage source inverter. Rolls-Royce International Research and Development (IRD) have been concentrating on one particular form of permanent magnet synchronous motor, known as the transverse flux motor (TFM). This offers particularly good torque density in addition to low vibration signature and high reliability. Development of the TFM at IRD has progressed from initial feasibility appraisal through to detailed design studies, experimental rigs and materials investigations and work is now commencing on a 3 MW demonstrator motor which is being built under funding from the UK Ministry of Defence.