Design and optimization of an IPMSM with fixed outer dimensions for application in HEVs

Permanent magnet excited synchronous machines (PMSM) are finding more and more applications nowadays. They are particularly well adapted when a high power to volume ratio or a high overall efficiency are required. This is in particular the case for hybrid electric vehicles (HEV), due to the limited space available in drive trains and the severe constraints on fuel consumption. PM-motors are therefore the most widespread machine type in parallel HEVs. This paper presents the design and optimization of an internal PM-motor (IPMSM) under the constraint that the outer dimensions of the machine are fixed. The optimal rotor radius and the appropriate pole pair number of the machine are determined by means of analytical calculations and finite element (FE) simulations. A geometry optimization is performed, considering all losses (i.e. copper-, iron- and eddy-current losses), as well as the demagnetization resistance and the effect of centrifugal forces at high rotational speeds. In order to determine the field weakening capability and to generate the speed-torque as well as the speed-power characteristics, the direct- and quadrature-axis inductances are calculated in function of the load current and the field weakening angle.