Austin Jin with advisor K. Haran

Because of environmental concerns about increasing use of jet fuels, there is a call for more environmentally friendly and fuel-efficient aircraft. Our project aims to address this goal by implementing high frequency, high-pole designs for high power density electric machines. Among various machine topologies, permanent magnet synchronous machines (PMSM) are chosen because of their high torque density and efficiency. However, a major concern in PMSM is demagnetization of the permanent magnets used in the machine. It is highly resource-consuming (and expensive) to restore rare-earth magnets from irreversible demagnetization.

Current work aims to quantify and characterize demagnetization in the proposed high power density design. Figure 13 gives preliminary results using finite element analysis that show the vector field distribution of the B-field in the current neodymium iron boron (NdFeB, N45UH) magnets at 120 C, with three different load conditions. Note that the demagnetization analysis is closely related to the magnitude of demagnetizing current and operating temperature. Because the current magnet selection may experience irreversible demagnetization at 150 C when magnetic flux density inside the magnets is forced to approximately 0.3 T (where its “knee” is located), the choice of material may have to be reconsidered. Specifically, an alternative may be samarium cobalt magnet (SmCo), as it is more resistant to permanent demagnetization at higher temperatures.

This work, supported by NASA, is in the process of incorporating analytical field analysis of permanent magnets and characterizing demagnetization analytically.

Figure 13: Flux density vector field distribution with usage of NdFeB magnets (N45UH) at 120 C under three electric load conditions: no-load (left), full-load (middle), fault current (right)