Design of IPM Machines for Traction using Rare-Earth-free Iron-Nitride Magnets

For automotive applications, permanent magnet synchronous motors are the most common and usually contain rare-earth permanent magnets, such as neodymium magnets. The use of this type of magnet guarantees high efficiencies, torques and power densities. However, rare earth elements have a high cost and there is concern about the stability of supply and environmental damage caused by their extraction. For this reason, efforts are now being made to find an alternative to the use of rare-earth magnets, i.e. rare-earth-free magnets, in all sectors that require permanent magnets, including the automotive industry. During this thesis work, carried out in collaboration with the company Volvo Cars, a synchronous motor with internal permanent magnets was designed using rare-earth-free magnets, mainly composed of iron and nitrogen, elements that are among the most abundant magnetic materials on Earth. After designing a benchmark motor with classic neodymium magnets, I moved on to design a motor that would be able to exploit rare-earth-free magnets in the best possible way, overcoming the main problems that these new materials have presented so far, namely their low resistance to demagnetization. To do this, I used the open-source software \mbox{SyR-e} and its function syrmDesign, which in the course of this work was enhanced with a function that allows demagnetization to be taken into account even during the preliminary design process. Once the final design was defined, the geometry was optimized using JMAG software. The aim was to achieve the desired targets by minimizing the materials used and improving the behaviour of the magnets against demagnetization as much as possible. Two different optimizations were carried out and finally, the results were reported for each design and a comparison was made to highlight the pros and cons of these new materials.