| Back in the fifties of last century, Soviet scholars Zhdanov had proposed voltage stability problems. But until the seventies of last century, there has been many cases of voltage stability problems around the world, especially, the 814 United States and Canada blackout. The problem of voltage stability has been emphasis in the study of power system.Nowadays, our country is carrying out many major projects, such as:network interconnection all over the country, transport the power from west to east. The power system is developing to the direction of big unit, great power, high voltage and long-distance transmission. At the same time, our country is reforming the power system, gradually establish and improve electricity market. Because of the restraint of the economic and environmental, the demand of power will increase gradually in the future, the power system will more and more close to the limit. So the voltage stability will still be a problem that we must confront and solve.Thevenin equivalent, as a simple, intuition and practical method in the study of voltage stability, has been favor in many scholars. But there has not been a perfect theory or a simple method to solve this problem. so we focus on this defect try to find the correct way to solve the thevenin equivalent.This paper based on Thevenin equivalent, we made a lot of theoretical proof and formula, finally, we got the New Extended Thevenin Equivalent Dynamical Fundamentals. This paper creates a effective method to solve the difficult of Thevenin equivalent. As the equivalent potential and the equivalent impedance are coupling together, we based on the voltage is Analytic functions of current, to make sure that the voltage can be derivatived by the current in all over the complex plane. By this approach, we prove that if the load node wants to get the maximized power, it must follow this principle:the modulus of internal impedance should be equal to the modulus of external impedance. We study the New Extended Thevenin Equivalent Dynamical Fundamentals by a clever idea to transform the PQ bus and the PV bus. We found out the Physical meaning of the Thevenin equivalent by the idea of how to change the PQ bus and the PV bus. In the multi-machine system, the impedance model of the New Extended Thevenin Equivalent Dynamical Fundamentals, can analysis the voltage stability and the angle stability of the power system at the same time. This is the most important theoretical contribution of this method. We made this method and its advantage is clear, such as computing speed, accurate calculation, efficient. The results proved that the impedance modulus margin can be clearly reveals the weak point of the system. in particular, comparison on the results of CPF, this method can be proved very correct. This theory provides a effective method to study and analysis the voltage stability of the power system. |
