Tentative Study On The Influence Of Non-Differential Components To Power System Small Signal Stability

Under deregulation environment, power systems are operated even more close to its stability limit to obtain more profits, so power system stability and security are paid more and more attention. Power system is a typical nonlinear dynamic system, there exist many non-differential components, such as hard-limit of the exciter, dead band, hysteresis, tap changing of the OLTC, etc. It is an important task to make study on influence of the non-differential components to power system stability. In this thesis, we mainly discussed the impact of exciter limit on power system small signal stability and small signal stability region.Firstly, a unified expression method is introduced to describe the piecewise, continuous function. All non-differential points are converted into the poles of its derivative function. And the left-hand derivative limit and the right-hand derivative limit can be used to approximate the derivatives at such points according to the requirement.Secondly, based on the proposed method and a simple three-bus system, the impact of the exciter limit to power system small signal stability and small signal stability region is deeply discussed. We find that the exciter limit can change elements of the system Jacobian matrix so as to cause jump of the system critical eigenvalue. New Hopf bifurcation and new oscillation mode can also be triggered when exciter voltage hits its limit. In additional, exciter limit can cause significant topological changes to the power system small signal stability region. e.g. Exciter limit can cause new instability hole in the small signal stability region and make the region boundaries more complex.Finally, the proposed method is compared with the polynomial fitting and Fourier fitting methods to reveal its effectiveness.There are so many non-differential components in power systems, they should be correctly considered in various stability studies.