An Improved Model for Saturated Salient Pole Synchronous Motors

An improved model for the transient analysis of saturated salient pole synchronous motors is presented. With the aid of saturation factors obtained by means of test or finite elements, Park´s equations for a synchronous machine are modified to independently account for the saturation of the d and q-axis magnetizing flux linkages in the region of the stator teeth and rotor pole fact as well as saturation of the total flux linking the stator core. The model is used to calculate the starting performance for a direct on line start as well as the transient performance during a load change. Both transients are correlated with both test results and the results predicted by a traditional model employing only d-axis main flux saturation. The new model demonstrates an improvement over more traditional models indicating that an appropriate representation of the main flux and core saturation effects are important for synchronous machine analysis. Figure 1 shows the complete equivalent d-q circuit model developed in the full paper. The inductance Lsa represents the reluctance of flux lines which are primarily in air. Lsc represents the magnetic reluctance of the stator core, Lsb accounts for the leakage inductances which are primarily iron related, i.e., slot leakage, tooth top and harmonic leakage. Lmd, Lmq account for the magnetizing flux linkages representing the MMF drop in the stator tooth top and field pole. In general, all of these inductances except Lsa can saturate.