Influence of the Lamination Material and Rotor Pole Geometry on Performance of a Wound Field Synchronous Machine

This thesis investigates the influence of different lamination materials along with rotor pole geometry on the performance of a Wound Field Synchronous Machine. Both Non-Oriented (NO) and Grain-Oriented (GO) laminations are analyzed with the original and modified rotor structure to recognize how generator operation is affected. In the first part of this work, the state-of-the-art of NO and GO steel sheets is examined and nine materials from different manufacturers are selected on the basis of their permeability and power loss figure. Due to an incomplete characterization of the selected materials, i.e., low field measurements of magnetization curves, several methods for extrapolation to high field values are evaluated. Such an analysis demonstrates that an inaccurate modeling of macroscopic magnetic properties strongly affects the accuracy of electromagnetic simulation results, providing significant research value. An exponential law of extrapolation is validated as the most effective when it comes to extending low field measurements data up to saturation. A review of different iron loss models for electrical machine applications is carried out afterward. An approach capable of calculating the loss figure under nonsinusoidal flux density waveform, considering power loss separation into hysteresis, classical and excess components, is chosen for the investigations. In the second part, the 2D CAD model of the benchmark machine is built based on measurements received from the lab. Its behavior is studied through the Finite-Element Analysis using Altair Flux 2D software package. Several machine models are evaluated keeping the same stator laminations and rotor pole geometry. A comprehensive assessment of some technical parameters such as output power, torque ripple, power factor and iron losses, allows to investigate the influence of NO and GO rotor lamination materials on machine performance. The use of a GO steel sheet provides minor advantages. However, more investigation is needed to quantify the iron loss figure and to compare it with the benchmark machine. Considering NO laminations, the highest increase in terms of output power around 1% is obtained with a high–loss NO steel (M700 50A); this variation lies within the experimental uncertainty band. As a consequence, another machine model, with both stator and rotor M700 50A laminations is evaluated in an attempt to achieve a better performance improvement. Such a model is able to reach an output power improvement around 4%. In the third part of this thesis, the latter machine model is compared to the benchmark at constant output power. By modifying its rotor pole geometry with three different strategies (pole–arc radius adjustment, pole–neck width adjustment and d-axis air-gap adjustment), it is possible to reach the reference output power obtaining lower torque ripple and a reduction of rotor mass.