Analysis of Saturated Synchronous Machine considering d-q Axis Coupling Reactance

The present paper describes a study of small signal performance of synchronous machines connected to a large power system network through transmission line under steady-state operation by considering influence of saturation with cross-magnetizing phenomenon between d- and q-axis circuits. In the method, mutual reactance due to the cross magnetizing phenomenon can be consider on the basis of d-q axis magnetic field analysis. The quantitative accuracy requires the magnetic coupling between d- and q-axis circuits be considered. Subsequently, steady-state reactances are analyzed by considering mutual reactances due to cross magnetizing phenomenon. Synchronous machines have a nonlinear characteristic due to saturations and cross-magnetization phenomena, so that d-q axes inductances vary depending on the current amplitude and the load angle. Therefore, usually the uncoupled d-q model with constant parameters might not be suitable to represent accurately the performance of the electrical machine.