Analysis of rotor eddy current loss in fractional slot permanent magnet machine with solid rotor back-iron

摘要

This paper analyses the eddy current losses induced in the permanent magnets and rotor back-iron which is made of a solid piece of mild steel. Time-stepping finite element method (FEM) is employed for simulation of fractional slot surface-mounted permanent magnet brushless machine having 12 slots / 10 poles and concentrated windings when the magnets are isolated / non-isolated and magnetized / unmagnetized. For the prototype machine the eddy current density analysis shows that eddy currents in the magnets are resistance limited and in the rotor back-iron they are non resistance limited. One of the major new findings is that eddy currents in the rotor back-iron are very sensitive to the changes in operation point of the BH curve of mild steel, and hence the machines with solid rotor of mild steel have to be analyzed with magnetized permanent magnets.