Rotor surface ferrite magnet synchronous machine for generator use in a hybrid application — Electro-magnetic and thermal analysis

To reach a particular tangential stress in a PMSM the magnetic loading and the electric loading should have corresponding values. This means that if the magnetic loading is restricted by the characteristics of cheap and relatively weak ferrite permanent magnets, the electric loading should be increased to keep the tangential stress at desirable value. However, the latter is also limited because of the demagnetization risk of the permanent magnets by a high armature reaction. Therefore, surface ferrite PMSMs should have a low tangential stress in order to avoid the demagnetization risk, which consequently leads to a low torque density. This is one of the main drawbacks of ferrite magnets used in electric motor drives. This paper describes some possibilities for improving the torque density with surface ferrite PMSMs, describes the restrictions which one can meet while designing this type of the electric machines and observe the influence of temperature variation in the magnets on the electric machine performance. An example is done with the analytical and the FEM analyses of a 50 kW, 3000 rpm, permanent magnet generator for a series hybrid electric vehicle application.