Design of Large Permanent Magnetized Synchronous Electric Machines: Low Speed, High Torque Machiines - Gererator for Diriect Driven Wind Turbine- Motor for Rim Driven Thruster
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- Institutt for elkraftteknikk 
This work presents the design of two prototype permanent magnetized electric machines for two different applications where large permanent magnet machines might be used. Existing technology have been used as the fundament for new design and adapted to new applications, contributing, hopefully, to the development of better and more environmental friendly energy conversion. The first application presented is represented with a prototype made in cooperation with the industry in which a PM-motor is integrated into a propeller unit. Both because of the industrial connection, and the integration between the PM-motor and the propeller, the choices made for the PM-motor are conservative trying to reduce the risk. The direct rim driven thruster prototype includes a surface mounted radial flux permanent magnet machine (SM RFPM) with fractional slot winding with a q around 1. Other engineering features were introduced to make the integration of propeller and motor feasible, but without the PM-machine the thruster would not have reached the performance demand. An important part of the project was to show that the SM RFPM enables this solution, providing high performance with a large air gap. The prototype has been tested in sea, under harsh conditions, and even though the magnets have been exposed directly to sea water and been visible corroded, the electric motor still performs well within the specifications. The second application is represented with a prototype PM-generator for wind turbines. This is an example of a new, very low speed high torque machine. The generator is built to test phenomena regarding concentrated coils, and as opposed to the first application, being a pure academic university project, its success is not connected to its performance, but with the prototype’s ability to expose the phenomena in question. The prototype, or laboratory model, of the generator for direct driven wind turbines features SM RFPM with concentrated coils (CC). An opportunity to push the limits for the design was given, and taken, choosing a relative high frequency and open slots to investigate the consequences of large reluctance variations in the air gap and distorted MMF. The main purpose of the PM generator is to explore a very low speed machine with high pole number and concentrated coils with coils wound around every other tooth. The study leading to the design included a discussion of scaling of the prototype from the full size generator, which parameters to keep, which to stress and which to forget. An investigation of the winding layout and winding factors included building a smaller table model for testing of different winding configurations, was also an important part of the work. Though the prototype has its flaws, or experimental setbacks, it successfully enhances the characteristic of the low speed, high pole number and slot geometry focusing on the harmonic content of the MMF and the consequences for the losses and reactance.