Identification of the technical potential of permanent magnet Flux-Switching-Machines compared to rotor-excited PM synchronous machines

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In conventional permanent magnet synchronous machines, the magnets (e.g. neodymium-iron-boron-(NdFeB)-magnets) are on the rotating part (rotor), where only a limited cooling of the magnets is possible. Thus, typical continuous operating temperatures in the magnets are at 150 °C - 180 °C. So high continuous temperatures are only possible with NdFeB-magnets with additives (e.g. dysprosium) or samarium-cobalt (SmCo) must be used. SmCo-magnets have a lower remanence flux density and are more expensive than NdFeB-magnets, but also the dysprosium increases the cost of NdFeB-magnets significantly. Alternatively, the magnets of the machine can be mounted in the stationary part (stator). Due to this, the magnets are close to the stator cooling circuit and the temperature in the magnets can in general be kept below 100 °C. Therefore, cheap and highly remanent magnets with less or even without dysprosium can be used. The rotor of those machines is winding- and magnet-free and robust. In the stator, inexpensive tooth coils can be used, but the constructive fixation of the magnets must be designed rationally. Three different topologies with stator mounted magnets have gained increased attention in recent years: Doubly-Salient-Permanent-Magnet-(DSPM)-Machine, Flux-Reversal-Machine (FRM) and Flux-Switching-Permanent-Magnet-(FSPM)-Machine. Existing investigations suggest that the FSPM-Machine achieves the highest torque densities at the same thermal utilization. A goal of this project is the comparison of the three machines for a given performance requirement and to document quantitatively the expected advantages of the FSPM-Machine. Another aim of the project is to develop a methodological approach for the design of Flux-Switching-Machines in the power range up to 150 kW as high-torque drives for the lower and medium speed range up to 3000 /min. The electromagnetic, thermal, mechanical and constructive design criteria should be worked out in coordinated steps and validated by measurements using a prototype machine. A prototype of the Flux-Switching-Machine should be compared with a comparable, at the Institut für Elektrische Energiewandlung available, conventional PM synchronous machine with regard to the achievable electromagnetic utilization, efficiency, converter utilization and the performance in case of a failure (such as a short circuit).From that, general applicable design rules for Flux-Switching-Machines should be derived and the advantages and disadvantages of this type of machine should be emphasized compared to conventional machines.