LOCAL STABILIZATION OF A SINGLE-MACHINE SYSTEM USING THE DIRECT NYQUIST ARRAY METHOD

There is a need to recast the results concerning the power system stab ilizer in the new language of geometric nonlinear dynamics. This will serve to give a better insight into the success of these devices, and it will also highlight their limitations. It is shown in this paper th at the power system stabilizer problem stems from a subcritical Hopf b ifurcation that occurs in a detailed model of a single machine infinit e busbar system that includes a fast exciter. As such the problem is p osed as a local stabilization problem of a nonlinear model. This expla ins the reason why a linear design works to stabilize the nonlinear mo del on the basis of Liaponov's theorem of stability. It also emphasize s the need to consider the global features of the system by considerin g the full nonlinear model. The direct Nyquist array is used as a desi gn methodology for evaluating measurable signals in the linearized mod el. We demonstrate the effectiveness of speed deviation, electrical to rque and line current for stabilizing the linear model. The line curre nt signal has not been considered in the literature previously, except that we proposed its use for stabilizing subsynchronous resonance.