Evaluation of the Rotor Eddy-Currents in High-Speed PMSMs with a Shielding Cylinder

A continuous demand for more efficient and more compact drives is pushing the popularity of high-speed permanent-magnet synchronous machines. However, high rotational speeds and extreme power densities imply that an appropriate cooling of the rotor may be difficult. This is all the more important because of the risk of demagnetization when permanent magnets are operated at high temperatures. Therefore, it is paramount to reduce the losses in the rotor of highspeed machines as much as possible. One technique to reduce the eddy-current losses is introducing a shielding cylinder, i.e. a conductive sleeve that is wrapped around the magnets. However, when badly designed, such a shielding cylinder may increase, rather than decrease, the losses. Therefore, an in-depth study of the effect of the shielding cylinder on the eddy-current losses in high-speed PMSMs is required. By studying how the eddy-current losses are affected by the shielding cylinder's thickness and its conductivity, this work aims at providing more insight in how the eddy-current losses can be reduced.