Analysis Of Steady Voltage Stability In AC/DC Power System

The power system is a nonlinear dynamic system, whose stability is paid much attention to by the electric power engineers all along. These years as HVDC lines are put into operation, it calls much influence to the character of power system and makes the stability of the system is faced with more challenge. This paper researches on the static stability of the AC/DC power system.On the base of analyzing the advantage and disadvantage of several continuation methods in common use, for example, the local parameterized continuation method and the arc length parameterized continuation method, an improved continuation method is brought forward. Based on the character that the step has much influence on the iterative times and the convergence, the optimization precept of the step is raised and then through the calculation of the New England 39 Bus system testify that this method advances the calculating speed in the meanwhile of maintaining the precision.After the research on the calculation of the worst parameter direction and the closest voltage collapse point which are the problems the running personnel mainly concern, an intuitionistic definition of the closest voltage collapse point is proposed, and the relationship between the normal direction of the voltage collapse boundary surface and the left singular vector of the Jacobian matrix at the closest voltage collapse point is argued. And then a method for attaining the worst parameter direction and the minimal load margin quickly with the improved continuation method is put forward. In this method, the initial load increasing direction is appointed at discretion, then the voltage collapse point in this direction is calculated. Then repeat the calculation with the left singular vector of the Jacobian matrix at the voltage collapse point as the next parameter direction until the superposition of the two occurs.This paper decompounds the AC system equation and the DC system equation, takes the coupling relationship of the AC/DC system into account through the relation equations between the state variables of the DC system and the ac bus voltage of the converter station and the presented DC parameters, and then generalizes this method to AC/DC power system, forms a kind of methods for calculating the worst parameter direction and the minimal load margin in AC/DC power system.In the end, this paper researches on the confirming method of the optimum controlling direction and the measures to improve the steady voltage stability in the AC/DC power system.