The Research For On-line Voltage Stability Considering Load Characteristics

With the accidents of voltage instability have been occurred frequently and the growing demand in electricity, power system operation is more closer to its critical state, voltage stability problems become to be increasingly serious, the voltage stability problem is getting attention. Meanwhile, the voltage stability problem is also called load stability, the study of load characteristics on the impact of voltage stability problem is particularly important. In this paper, on-line voltage stability problems have been researched based on three different load models.1) Voltage stability margin, all kinds of operation state, has been calculated by continuous power flow. Then a three-layer neural network model has been designed, which establishes a mapping between the changes of node load and voltage stability margin. The input vectors of neural network model are used the method of regression analysis for feature selection, in that reduces the dimensions of input in purpose of speeding up the training and improving the training precision, which overcomes the disadvantage of online-calculation is slowing by continuous power flow.2) A local equivalent method which is based on time section is presented. For a researched node, The power grid is equivalent to a two-node system which is composed of a load and a power generation, works out the local equivalent model parameters by using PMU measured voltage and current phasors. Takes static ZIP model as load model, voltage stability index expression is derived, no need of computing the network equivalents, which will improve the accuracy and computation speed.3) Equilibrium manifold is tracked by continuous power flow, then in the obtaining equilibrium point, establish a dynamic load model which is composed of induction motor and a parallel resistance, pushs out a differential algebraic equations model of a simple power system of voltage stability analysis, analyzes the small disturbance voltage stability which is considered the dynamic characteristics of the load, and a voltage stability dynamic index is derived.