In this paper a scaling approach for the solution of 2D FE models of electric machines is proposed. This allows a geometrical and stator and rotor resistance scaling as well as a rewinding of a squirrel cage induction machine enabling an efficient numerical optimization. The 2D FEM solutions of a reference machine are calculated by a model based hybrid numeric induction machine simulation approach. In contrast to already known scaling procedures for synchronous machines the FEM solutions of the induction machine are scaled in the stator-current-rotor-frequency-plane and then transformed to the torque- speed-map. This gives the possibility to use a new time scaling factor that is necessary to keep a constant field distribution. The scaling procedure is validated by the finite element method and used in a numerical optimization process for the sizing of an electric vehicle traction drive considering the gear ratio. The results show that the scaling procedure is very accurate, computational very efficient and suitable for the use in machine design optimization.

Gapped magnetic components are inherent to applications where conversion of power would force magnetic flux density beyond the saturation point of magnetic materials. A physical discontinuity in a magnetic path, which an air gap represents, signifies a drastic change in its reluctance to magnetic flux. This gives rise to a phenomenon referred to as the fringing effect, which impacts the performance of magnetic components. The fringing flux also affects the physical properties of magnetic components, such as magnetic reluctance and inductance. Since inductance of gapped magnetic components is a function of the size of the air gap, a relatively simple change to the configuration of the air gap or splitting a single gap into a plurality of gaps entails, frequently, a radical change to the magnetic circuit of the component. This paper examines the way the air-gap configuration affects the distribution of the fringing flux and, by extension, magnetic reluctance and inductance. A method to aid the design of multigap inductors is presented based on 3-D electromagnetic modelling as well as measurements. An analytic expression, which closely approximates the required length of quasi-distributed gaps substituting a single gap, is developed.