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Currently, due to the growing use of renewable energy technologies and hydrogen energy technologies, highspeed electric machines are of particular interest. High-speed electric machines have proven themselves well in compressor units and can improve the overall efficiency of the entire unit by eliminating the gearbox. However, the design and operation of these electric machines are accompanied by several difficulties, such as the resulting increased centrifugal forces, leading to increased mechanical stresses in the structure of the rotor. In this paper, a high-speed synchronous reluctance motor is considered as the object under study. The aim is to investigate the possibility of reducing mechanical stresses in the rotor steel by optimizing its topology while maintaining the output electromagnetic power.

In the present paper, a new numerical model for calculating martensite microstructure in induction surface hardening processes is introduced. The model was developed with the help of the Department of Electrotechnology and Converter Engineering (LETI). It takes into account the heating as well as the quenching process and uses the temperature history of a work piece to calculate martensite formation. The calculation is based on an empirical equation found by Koistinen and Marburger [1]. A comparison between the heat distribution within a work piece at the end of the heating process and the distribution of martensite after quenching is performed for different process parameters. Thus, it is determined, in which case the temperature distribution is sufficient to predict the hardened layer and in which case the microstructure has to be calculated to receive accurate results. The model is verified by comparing simulation results with different experiments.