Rotordynamic analysis of different rotor structures for high-speed permanent-magnet electrical machines

A rotordynamic analysis of two different high-speed permanent-magnet electrical machines has been performed. Their rotors are analysed separately and for each of them the analysis is performed for three different types of constructions depending on the type of the retaining sleeve. The first type of rotor construction has a carbon-fibre sleeve for retaining the magnets against the centrifugal forces and an aluminium shield for eddy currents. The retaining sleeve of the second construction is made from the titanium alloy Ti-6%Al-6%V-2%Sn and the sleeve of the third type of construction is made from the titanium alloy Ti-2.5-Cu. The last two constructions are examined without additional eddy-current shields. A numerical, finite-element, rotordynamic analysis for each type of rotor construction is performed. The numerical model is successfully compared with measured results for the natural frequencies. The analysis in this study shows that the rotor constructions retained with the titanium alloy Ti-6%Al-6%V-2%Snsleeve provide better rotordynamic properties than the other types of rotor constructions.