High-performance synchronous reluctance motors by local manipulation of the magnetic properties of electrical steel laminations during the laser cutting process

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The synchronous reluctance machine is considered as a viable alternative to typically used permanent magnet synchronous machines and induction machines. Especially the tremendous rising of rare-earth magnet prices (e.g. NdFeB) and the resulting higher costs of PM-machines led to an increased interest in this magnet-free and therefore cost-efficient motor type. However, a broader application of synchronous reluctance motors is currently still prevented by the comparatively low power factors and power densities. The highly limited saliency ratio (or synchronous inductance ratio) between the d-axis and q-axis flux can be considered as the main reason. Theoretical analyses have shown that higher saliency ratios can be achieved by reducing the width of the leakage flux guiding steel bridges. However, that leads to a decreased mechanical stability of the rotor. The planned project analyses this problem in detail and aims for a significant higher saliency ratio by local manipulation of the electrical steel lamination properties during the laser cutting process. Contouring the sheet metal by laser cutting is characterized by a high number of degrees of freedom (cutting parameter set) compared to mechanical cutting processes (e.g. punching). This opens up the opportunity for an optimal local setting of magnetic characteristics dependent on the area of the electric machine. Furthermore, using the laser allows the manufacturing of highly filigree structures that cannot be achieved with mechanical methods. The project deals with detailed analysis of the potentials by using the laser for the cutting process of the electrical steel laminations for application in synchronous reluctance motors. The resulting impact on the operational behaviour of the machine is studied in theory and experiment. The analyses can be transferred to other motor types (e.g. PM-motor) as well, even though a lower influence on the machine behaviour is expected.The main objective of the project is a considerable increase of the saliency ratio (+ 25 %) in comparison to current synchronous reluctance motors without decreasing the mechanical stability of the rotor. This leads directly to higher power densities and power factors and therefore higher efficiencies as well. An important contribution to a more widely application of synchronous reluctance machines is expected.