Study On Voltage Security And Preventive Control Of Power Systems In Degregualted Enviroments

Voltage instability is widely recognised as a significant threat of power system blackout. Hence, voltage security assessment (VSA) is one of the most important tasks in control centers of power systems. With the opening of large electricity markets, in many countries, more and more power transactions have been established. Moreover, power systems often operate in unforeseen conditions since transactions follow different patterns than those assumed at the planning stage. Obviously, system operation is pushed closer and closer to its limits and there is a need for appropriate tools to identify dangerous contingencies, assess security margins and suggest preventive and corrective actions. Hence, VSA becomes even more important in the open assess environment and should be performed in control centers for operating points forecasted on the each hour of the next day but also in real time, in order to face unforeseen events. The TSO should evaluate security margin with respect to credible contingencies. In case of congestion, i.e. when security margin are deemed insufficient or when the system has no margin with respect to a plausible contingency, the TSO should determine the best preventive actions to restore such margins. This thesis is only devoted to several topics on the power system voltage stability and its preventive controls under the deregulated environment. Main research works and contributions are summarized as follows:(1) Aiming at the differential algebraic mode of power system at steady-state, this paper presents a systematic and adaptive continuation method for detection of saddle node bifurcation (SNB), limit induced bifurcation (LIB) and all the device limit points (LPs). Firstly, an adaptive step size control method is introduced for tracing of equilibrium manifold and detection of the SNB point. This step size control considers the curvature of the manifold and a quadratic interpolation polynomial is introduced to predict the next continuation point. Secondly, another predictor/corrector scheme is presented to find all the LPs and identify the LIB point. A systematic method tries to combine the two continuation schemes and lead to a more effective method for SNB, LPs, and LIB detection. The proposed method is demonstrated through several numerical tests. In our numerical experiments, the method is...