Mechanical and thermal designing aspects for a PM synchronous machine with wound rotor

In variable speed drives mechanical and thermal phenomena interfere with electromagnetic ones. When it comes to permanent magnets (PM) machines, beside the common problems related to the stator winding insulation damage at high levels of current densities, some supplementary issues are revealed at the rotor core: mechanical stress due to centrifugal forces while high speed is attempted or the irreversible demagnetization risk of the PM, since its operating point varies with the temperature. The paper presents the study of a PM synchronous machine with a supplementary field coil on the rotor. Analytical calculation and numerical computation through finite element method (FEM), accompanied by experimental tests, will reveal the behaviour of the proposed machine and will validate the applied design procedure in terms of safe operation.