Salient-pole rotor optimisations for synchronous generators using FEA software

This paper describes the influence of the graded air gap on the performance of a salient pole synchronous generator in terms of total harmonic distortion and air gap flux density waveform. Feasibility of redesigning an existing product to include the feature is also briefly discussed. The main focus of this investigation is the THD improvement for a skewless machine and the required increase in the excitation current due to the increased equivalent air gap when a salient pole machine is designed with graded air gap. In order to reduce the design time an optimisation solution was chosen to deal with this problem using 2D FEM. The optimisation produces theoretically sound outputs which provide a good understanding into the potential overall benefits in using a graded rotor pole design for salient pole synchronous machines. It is shown that the THD is reduced by a significant percentage with a small increase in rotor field current.