EVALUATION OF STEADY-STATE STABILITY OF DUAL-EXCITED SYNCHRONOUS MACHINES

Dual-excited synchronous machines have, in comparison with the conventional ones, the main advantage that it is possible to decouple their excited magnetic field axis from their physical pole-axis. By adjusting the excitation of the two field windings of these machines, their rotor angles can be regulated and, as a result, their damping torque can be increased to achieve the optimal steady-state stability performance. In this thesis, a generalized mathematical model for the dual-excited (d- and q-axis) synchronous machines is derived. Based on this model, a reduced-order model, which can be used with an acceptable accuracy to determine the swing mode eigenvalue of these machines and to calculate their damping torque coefficients, is developed. Using this reduced-order model, the steady-state stability performance of a dualexcited synchronous generator connected to an infinite bus as a function of both the rotor angle and the output power has been investigated applying both the eigenvalue and damping torque techniques. In this context, the cases with and without excitation controllers using a terminal voltage signal have been considered. These investigations have allowed the identification of the operating rotor angle ranges for the optimal steady-state stability performance of these generators. Moreover, a sensitivity approach has been applied to explore the effect of the change in some of the generator and excitation controller parameters on the steady-state performance of dual-excited synchronous generators when they are operating within these optimal rotor angle ranges