A comparison of hybrid excitation solutions for single-axis and bi-axial synchronous machines

Hybrid excitation synchronous machines are a class of machines that allow to reduce PM costs while keeping high torque density and that guarantee very high constant power speed range. They come in a wide variety of topologies and not all possible solutions have been explored yet. Aim of this paper is to provide a systematic analysis of all the possible configurations that can be obtained by changing the axis along which the hybrid excitation is placed. Both single-axis and bi-axial excitations are considered. A comparative analysis is carried out with respect to performance indices like torque capability, constant power speed range, power factor and losses.