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Novel Approach for Estimating Slot Filling Factor in FEA Based Design of Electrical Machines

A novel methodology is proposed for estimating the slot filling factor of random-wound single-layer and double-layer windings that can be easily included into Finite Element (FE) based design of electrical machines. Although several algorithms have been proposed in recent publications for maximizing slot filling factor of single-layer windings for a given conductor diameter and given slot geometry, no methodology for including these algorithms into machine design procedures has been proposed so far. Consequently, design of electrical machines, even if optimization is involved, is still often conducted under the assumption of empirically adopted constant value of the slot filling factor, resulting in suboptimal machine designs. This observation is especially relevant for metaheuristic electrical machine design optimization, where the slot geometry and number of turns per slot are constantly varied during optimization in order to maximize torque density or machine efficiency and where the assumption of constant slot filling factor is not justified. For this reason, a new approach for finding the optimal value of standard conductor diameter that yields maximum slot filling factor for each simulated machine is developed in this paper. Results of slot filling factor estimation by the developed procedure are presented for a Rotor Permanent Magnet Flux Switching (RPMFS) machine equipped with either a single-layer or a double-layer winding. It is demonstrated that the proposed approach maximizes torque density and minimizes losses for given dimensions of machine laminations, rated voltage, speed and torque.