Analytical-Numerical Model for Synchronous Homopolar Machines

Synchronous homopolar machines represent a viable solution for applications requiring a robust electro-mechanical conversion system. Their diffusion is hindered by the low power density and by their complex three-dimensional magnetic behavior which requires time-consuming 3D finite element analysis for the performance prediction. This manuscript proposes a general analytical electromagnetic model able to evaluate the performance of both split and pass-through winding layouts addressing the existing methodological gap of the literature. The modelling approach - based on equivalent winding and permeance functions - reduces the resolution of the 3D electromagnetic problem to two axially coupled 2D problems considering all the mmf contributions, including the end-winding one, which cannot be neglected for the split winding configuration. The analytical model is numerically implemented and its predictions are compared with the 3D FE analysis. The comparison demonstrates the effectiveness of the proposed model in estimating the performance in different operating conditions and any rotor position. Several experimental tests are carried out on a laboratory-scale prototype to validate the analytical predictions in terms of inductances vs. rotor position and voltage waveforms. Although the experimental assessment shows the limitation of the proposed technique, i.e. the linear magnetic behaviour, this could potentially serve as a basis for the fast design optimization of this machine topology.