The stator winding is known to be a key factor to enhance the performance of electrical machines in terms of efficiency, lifetime, volume and consequently the costs. Therefore, the selection of the suitable winding technology and a proper design are mandatory to fulfill the challenging requirements defined by transportation electrification. The paper deals with the comparison of stator winding technologies to be used for high speed electrical machines for propulsion applications. The most commonly used winding configurations in automotive applications such as stranded wire and hairpin are compared with an innovative winding solution featuring formed litz wires. The analysis is carried out by comparing the main figures of merit such as the phase resistance, the AC loss factor and the thermal behavior of the different winding configurations. The reference machine explicitly designed for the analysis is a 24 krpm Permanent Magnet assisted Synchronous Reluctance Machine featuring a peak power of 200 kW. The performance assessment, supported by analytical and numerical electromagnetic and thermal simulations, highlights the main features of each design solution.
A model for estimating the total eddy current losses in ring ferrite cores is proposed, which is based on a microstructure model of the electrical parameters of the material (conductivity and permittivity) and on the solution of the wave equations in the core. The presented model, combined with state of the art estimation of the hysteresis losses gives good agreement with the core loss measurements, over a wide range of frequency (10 kHz to 700 kHz).
A material model for ferrite is presented, enabling an accurate calculation of the core losses from 100 kHz to 1000 kHz with a single set of scalar parameters over a decade of excitation current. It is based on the modelling of different material effects such as quantum tunnelling conduction between ferrite grains and atomic level magnetisation. The implications of the satisfying results of this approach on core loss modelling techniques at high frequencies are discussed.
To calculate ferrite core losses based on a physical approach, non-linear material effects must be considered. To implement these effects in a fast and accurate way, a new semi-analytical model is proposed. It combines the solution of the wave equation in the core with advanced material models of ferrite into an iterative procedure. The results validate the approach, which enables a fast calculation of the core losses.
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