A new model for the saturated synchronous machines using the intermediate-axis saturation characteristics

The effect of saturation in synchronous machines is usually represented in their two-axis frame models by using their saturated d- and q-axis synchronous reactances. These saturated d- and q-axis synchronous reactances are obtained by modifying their unsaturated values with appropriate saturation factors corresponding to the voltage behind the leakage reactance. In practice, this technique fails to give good agreement to the measured values due to the fact that the cross-magnetizing effect (magnetic coupling between the direct and quadrature axes) is ignored In this paper, an innovative model for the saturated synchronous machines using the intermediate-axis saturation characteristics is proposed and, thus, the cross-magnetizing effect will be included explicitly. To verify the accuracy of this proposed approach, experimental investigations were carried out on a number of laboratory synchronous machines of different designs. The calculated field currents and load angles of these machines by the proposed approach have been compared with the measured ones.