Research On Calculation Method Of Critical Values Of Static Voltage Stability

In recent decades,frequent voltage instability made many scholars devote themselves to studying the problem of voltage stability and made many achievements. Especially, in the field of static voltage stability appears more achievements. In the study of static voltage stability, critical point values can calculate voltage stability margins reflecting the stability level. So efficient and precise calculation methods were paid close attention.In this paper, the voltage instability accidents were reviewed, the essence of critical point and recent calculation methods are illustrated.while Aiming at methods for calculation of static voltage stability critical parameters, this paper proposes a new changeable step integration strategy for determination of crisis parameters of static voltage stability based on load admittance model, which integrates dynamic step characteristic progress and equal continuation characteristic progress. Firstly, maximal power point closest to crisis point is calculated in the first progress quickly, namely, tracing calculation of the Thevenin's equivalent impedance during increasing the loads, then, the admittance corresponding with it is accumulated as the load admittance value for next power flow calculation. Thus, the transition from initial point to the maximal power point is with quick unequal step. The second progress successes after the first progress for transition from unequal steps to equal and exact determination of crisis parameters by equal step, namely, the maximum power point can be used as the beginning to calculate parameters of static voltage stability by equal step. DDF (directional determination factor) is created to achieve reasonable transition between two progresses. Finally examples of IEEE9, IEEE30, IEEE118 show the validity and accuracy of the strategy, which can propose a new tool supporting analysis of voltage stability.