Modulation behaviours and interchangeability of modulators for electrical machines

Abstract

The authors aimed to investigate the modulation behaviours and the interchangeability of three kinds of modulators in electrical machines, which are short circuited coil, salient pole reluctance and flux barriers, to understand the evolution of the modulator and reveal their individual action mechanism based on the general airgap field modulation theory. The modulation behaviours are systematically analysed and compared, including the modulation principles of the improved short circuited coil, the relationship between salient pole reluctance and pole arc together with slot opening depth etc., based on which the key rule of interchangeable modulators is summarised. Although different modulators possess different magnetic field modulation principles and magnetic conversion capabilities, they share the similar asynchronous behaviours and modulated harmonics distribution. In addition, the detailed topological analysis of traditional brushless doubly fed machine with interchangeable and combined modulators is presented to show the effectiveness of the theoretical investigation. Electromagnetic performances comparison, such as airgap flux density distribution, cross coupling ability, general torque performances and inductance characteristics, of a brushless doubly fed machine with different modulators are provided to reveal the relation between the machine performances and magnetic field conversion capability. Theoretical predictions are verified by 2-D finite element analysis and experimental measurements.