Power System Static Voltage Stability Fast Assessment And Preventive Control

In recent years, the large-scale wide area interconnected electric network and deregulated market environment of power systems have driven the operation of power systems closer to their limits than ever. Thereby, issues of voltage stability become more prominent than ever. Insuring power systems voltage operating safely and stably under complicated operating conditions has become a rigorous challenge to electric utilities. Voltage stability project of Hunan power grid as the background, in this dissertation an attempt is made to implement effective online voltage stability monitoring. The contents include fast assessment methods for power system static voltage stability and its preventive control approach. The following are the main contributions of this thesis:A novel fast accurate algorithm of calculating node voltage under the N-1network topology is proposed based on branch MVA power sensitivity in this paper. The pre-contingency voltage is calculated based on Newton power flow approach. The derivative of voltage with respect to branch MVA power is calculated by using the convergent power flow equation of the base network topology. So, the post-contingency node voltage is obtained by using MVA sensitivity. The coefficient matrix for different branch outage is identical, it is not necessary to factor the coefficient matrix repeatedly; And because of good linear relation between node voltage and branch MVA power, the advantage of the proposed approach is its high speed and high accuracy.The calculation of critical point is an important issue in the field of power system static voltage stability research. A fast sensitivity based algorithm for the determination of critical point was presented. The feature of the proposed algorithm is that not need to use power flow Jacobin matrix of critical point; Base on sensitivity technology, load increments step be reduced automatically with the slope of PV curve increased; During the processing for approaching the SNB point, reactive power limits of all generators is considered, and it can be used to determine the reactive power/voltage type conversion and identify critical point. The value of critical point can be calculated accurately as local curve fitting is close to the critical point.Based on fitting equation which was used to calculate the critical point, a new method is derived to compute the sensitivity of loading margin to voltage collapse with respect to any parameters. Differing from the traditional one, this method does not not need to compute the left eigenvector associated with the zero eigenvalue of power flower flow Jacobian matrix, evaluated at critical point. What’s needed is just to the operating point is close to the critical point as possible used sensitivity guidance technique. Then, sensitivity information is obtained easily with fitting equation and information of fitting point. Avoiding the interation step to compute left eigenvector and fitting equation is only a single equation. Therefore, this method is more simple and more suitable for on-line static voltage stability analisis.An on-line prevention scheduling algorithm base on linear programming is presented. The feature of this algorithm is that Serious Contingencies and Unstable Contingencies can be solved in the same mathematical model; At the same time, virtual distribution factor is added, which low cost and no influence to state variable of base network. To increase the system static voltage stability margin, distribution factors is optimized used centralized scheduling. Under meetting the requirements of loading margin, the adjusted amount for actual parameter was reduced by this means. Especially, the adjustment about amount and frequency of active power output of the power plant was reduced, the negative impact to power plant is reduced simultaneously.Based on power systems static voltage stability fast assessment and preventive control algorithm which is mentioned in the previous paragraph, a monitoring Software of voltage stability is designed based on web. This Software in the server system is exploited by C++and Java programme language. Tests on IEEE standard bus system and Hunan power system verify the correctness and accurateness of this approach. Finally, this software is successful applied to on-line static voltage stability analysis of Hunan power system.