Modelig And Algorithm Of Steady-State Control Power Flow For Pfpf Problem And Its Using In Mid-Term And Long-Term Voltage Stability Calculation

From the eighties of the twentieth century, voltage stability has been a global focus to research in power engineering and academe. But different researcher sets out from respective study aspect and has different understanding of voltage stability mechanism, so for the same problem, he is likely to educe respective different conclusion for using different study method and model. Therefore, voltage stability is still a fresh subject full of challenge and fascination.In this complicated study background, this thesis deal with problems associated with the dynamic response of power systems to severe disturbance for studying mid-term and long-term voltage stability problems using QSS method introduced in recent years. Based on the new concept of PFPF (Postfault Power Flow) which proposed by P.Kundur, this thesisproposes the modeling and algorithm of steady-state control power flow for PFPF problem and applies it to mid-term and long-term voltage stability calculation. The main contents of this thesis are as follows:One, in order to resolve the power flow calculation problem how to determine the outputs of generator units for mid-term and long-term voltage stability analysis, this thesis proposes the modeling and algorithm of steady-state control power flow for PFPF problem and use reducing dimension algorithm to solve equations. This algorithm considers active power-frequency and reactive power-voltage static characteristics of generator units and it builds up the frameless foundation of PFPF method for large-scale power system.The second takes a study on mid-term and long-term voltage stability calculation. This thesis takes a study on the basic theory analysis of voltage stability from generator characteristics, transmission characteristics and load characteristics. At the same time, a simple AC line from physical origin is used to analyze the cause of leading to voltage collapse that voltage collapse phenomena develops when load demand exceeds the ability of generation systems, transmission systems. And then, this thesis establishes corresponding mathematical models for mid-term and long-term voltage stability from generator control characteristics, OLTC tap changing and load characteristics and proposes QSS algorithm for mid-term and long-termvoltage stability simulation. Finally, the simulation program for mid-term and long-term voltage stability is introduced to solve the problem.Vast numerical simulation tests and analysis of the proposed algorithm and the formulations have been applying to test on three test systems. It's demonstrated as follows. The algorithm of steady-state control power flow for PFPF problem needs not the assumption of PQ, PV and swing buses. This algorithm impersonally and correctly describes the automatic adjusting behavior of synchronous generator following a disturbance and is a very useful tool for mid-term and long-term voltage stability analysis. In mid-term and long-term voltage stability analysis, the test results shows that OLTC tap changing, OLTC control mode, generator current limits, reactive power limit and unfavorable load characteristics have effects on mid-term and long-term voltage stability. While the essential cause contributing to loss of system operating point and leading to voltage collapse is that load demand exceeds the ability of generation systems, transmission systems. At the end of the thesis, a discussion is given on the existing problems and the prospects for steady-state control power flow algorithm for PFPF problem.