Concept study of 20 MW high-speed permanent magnet synchronous motor for marine propulsion

High-speed permanent magnet synchronous machines are of great interest in the applications where high utilization factor and efficiency are required. Depending on application, power requirements change from kilowatts to megawatts. To investigate power limits of high-speed machines, the present feasibility study focuses on a 20 megawatt (MW) electric drive for marine propulsion. However, in addition alternative propulsion systems, ranging 100 kW to 20 MW, have been considered in an attempt to highlight some of the scaling rules that are apparent to high-speed machine considering their specific power level. In marine propulsion, the electric drive has to provide high torque at low speed to the propeller, however at different levels due to pole towing or open water operation. For electric drives, this tends to require high frequencies (large number of poles) as well as high currents. In general, ocean-going ships exist to provide affordable transport for cargo or passengers. In this respect, there exists a range of speeds within which virtually all ocean-going ships have operated and still operate. Within this range of speeds, roughly 10-30 knots, ship propulsion speed, in revolutions-per-minute (rpm), lie within a certain range, up to a couple of hundred rpm. The horsepower range coupled with propulsion rpm makes ship propulsion motor applications a high-torque, slow-speed electric drive. To deliver 20 MW propulsion power at a rotational speed of 150 rpm requires almost 1,300,000 newton meter (Nm) of torque. Emerging ship designs that employ different propulsion, e.g. water jets, may change this. However, in the following decades, ship propulsion motors will remain to be dominated by high torque, slow-speed motors, which are likely to remain for quite some time yet. In this respect, state-of-the-art ship propulsion motors are almost entirely alternating current (AC) synchronous wound field water cooled motors, or AC asynchronous induction motors. This report aims to give a general introduction to the concept of electrically-propelled vessels and presents specifically a feasibility study to a 20 MW high-speed permanent magnet synchronous motor (PMSM) to be used for ship propulsion. Although that also an initial attempt is documented to provide scaling laws for high-speed PM motor ranging from 100 kW to 20 MW. The purpose of this report constitutes a concept study and not an in-depth system analysis that would be required when implementing this technology for an electrical drive in future propulsion systems, such as ships or large vehicles. However, special attention is given to the apparent design challenges for these large high speed electric drives and their possible solutions