Dynamic Voltage Stability Study Considering STATCOM

As the inter-connection of large regional power systems will be put into a new stage with the rapid development of power systems in our country, the modern systems becomes a super large nonlinear dynamic system, including large capacity units, extra high voltage, long distance transmission, heavy load demand, inter-area connection and AC-DC power system parallel, etc.. With the advantages of inter connections among different areas, power exchange becomes more effective, optimal allocation of power resources is beneficial, and reliability of system increases.To maintain the security and the stable operation of power system is vital to the national economy and people's normal life. Voltage instability is widely recognized as a potential of power system blackout with the inter-connection environments. Although so much efforts and achievements to improve stability of power system have been made, it is still an important security issue that must to be considered in power system security operation. Flexible AC Transimission System(FACTS) technology bring a novel control means and application in system, the dynamic of power system with FACTS equipments and the control strategies of FACTS attracts significant interests of research.The thesis explores the negative influence of induction motor loads on voltage stability and presents the compensation effect of STATCOM. Aim at considering the dynamic process in voltage stability during voltage stability evaluation, a novel method based on Quasi Steady State (QSS) analysis and point estimate method (PEM) is proposed for voltage stability analysis in dynamic system considering STATCOM applications. To enhance transient stability control of power system, STATCOM control in multi-machine power system and the coordinated design strategies of STATCOM and generator excitation system are further studied as well.The main contributions of the thesis are as follows:(1) The effect of induction motor load on voltage stability and the compensation of STATCOM are studied. ZIP loads model is also been considered in comparison with induction motors about the performance in voltage stability. Detailed models of aggregated induction motor loads, STATCOM, generator and ZIP loads are presented, and time-domain simulation method is applied to assess the effects. The influence of induction motors parameters, e.g. mechanical inertia is also studied. Simulations show that STATCOM plays a notable role in voltage stability support for power system, especially for the system with large amount of induction motors.(2) Aim at considering dynamic process in voltage stability probabilistic assessment algorithm, a novel method based on Quasi Steady State (QSS) analysis and Point Estimate Method (PEM) is presented in this thesis for voltage stability analysis considering system dynamic action. QSS analysis may avoid large amounts of differential equations in the mid-long term,and a few deterministic computations are computed with the use of PEM to obtain the probabilistic distributions and probability of concerned bus voltage sags concerned. Uncertainties, such as random branch outages and nodal power injections may be conveniently considered. The effect of relativity among random variables can be also analyzed with the help of principal components analysis. The dynamic reactive power compensation effect of STATCOM in the system is also studied. Numerical analysis verifies the accuracy of this algorithm.(3) Considering that most power system models are Nonlinear Differential-Algebraic Systems, the Hamilton system theory is applied to design the control strategy of STATCOM. The model of STATCOM is presented first and the constrains including the control variables are built. Furthermor, the power injection based STATCOM model in multi-machine power system is formed for the Hamilton theory analysis. And the STATCOM controller in multi-machine power system is obtained. The case study of a 3-machine and 9-node system is used to validate its correctness and effectiveness of the method proposed.(4) The thesis presents a novel design of the coordinated control strategy of excitation system and STATCOM to improve power system transient stability and voltage stability. Based on the controllable reactive current source model, the third order state space modle including STATCOM is estabilished for a single-machine infinite system with nonlinear loads. By the use of generalized Hamilton theory, the control law of STATCOM output current I sand the excitation output voltage E f are proposed. Simulation results validate the coordinated control scheme.(5) The network of Shanghai 2010 is investigated for the var compensator equipment of Shanghai power system, and the dynamic voltage support ability of STATCOM in the security during operation and contingenciy is presented. Different allocations of STATCOM in different districts are examined. The simulation results by NETOMAC program show that STATCOM can improve the dynamic stability. The effect of STATCOM equipment capacity is also studied in the thesis.