DETERMINATION OF THE OPTIMUM ROTOR-STATOR DIAMETER RATIO OF PERMANENT-MAGNET MACHINES

Interest in permanent magnet machines has gained momentum with the int roduction of NdFeB alloys. However magnet cost is still relatively hig h and therefore design parameters have to be chosen carefully so as to minimize the volume of the magnet used for any particular application . This paper concerns the derivation of a mathematical expression that determines the optimum rotor/stator diameter ratio, known as the spli t ratio. in relation to other machine parameters. The analysis takes i nto account the demagnetizing effect of the load current on the magnet material and consequently the feasibility of the optimized design is examined. This analysis is then applied to several existing designs an d the results indicate that the appropriate choice of the split ratio would lead to a significant reduction in the magnet volume and hence i n the machine cost.