Variation of Saturated Reactances of a Salient-Pole Synchronous Motor in the Field-Weakening Region

Abstract

In this paper we present a method for calculating saturated reactances of salient-pole synchronous machines and calculate variations of reactances of a vector-controlled salient-pole synchronous motor using the method. We also consider the causes of the variations of reactances.The proposed method uses two-dimensional numerical magnetic field analysis and revised dq-axis equations in which the effect of the cross-magnetizing phenomenon is included. The values of the field currents calculated with the method show good agreement with the measured values.The method is used to calculate and analyze the reactances of the vector-controlled motor at various load points. The findings are as follows.(1) Numerical values of the mutual reactances between d- and q-axis xdq, xfq are not negligible.(2) Variations of the armature leakage reactance xl and the field leakage reactance xlf in the field-weakening region are considerable despite the small main magnetic flux.(3) The main cause of the variation of xl, xlf is saturation at the pole tips. This saturation occurs because of the difference between the armature m. m. f. distribution and the field m. m. f. distribution.