Application Research Of The Power System's External Network Equivalence

With the continuous development of power construction, in order to improve power quality and obtain high reliability, the power grids gradually become a huge interconnected system. However,various calculation and analysis under different running states on large power interconnected networks meets with the problems of computer capacity and time. In order to lessen the work and complexity, a simplified model of the external system is proposed to replace the original one.Generally, the external system equivalence consists of static and dynamic equivalence. And the static equivalence includes topological method and non-topological method according to the network topology.Compared with the non-topological method, the topological one only needs know the entire network topology and little information, so most of the current static equivalent methods are incline to topology method. In this paper, the ward static equivalence will be studied in detail. The existing shortcomings of the Ward equivalence will be found after studying the conventional and extended Ward method. And an improved method will be proposed according to the shortcomings. The new one will comply with the requirements of the project planning and the equivalent methods. Furthermore, gauss elimination will replace the original complex matrix operations while realizing the method.In addition, the dynamic equivalence based onε-coherent identification will be introduced. This method is divided into two major parts:ε-coherent identification of generators and the network simplification. In theε-coherent identification, the controllability Grammian for coherent generators are needed. The coherent generators will be gained after solving the Lyapunov equation. In the simplification part, coherent generators and external loads will be combined and simplified. This method has strict mathematical foundation. It avoids complicated calculation and this method is extremely efficient when multi-faults are analyzed at the same time, so it is widely used.Finally, this paper uses the 2006 Shandong 585-bus power system to verify the static and dynamic equivalent method. The scale of Shandong 585-bus power system is large enough and its data comes from the actual project, so it can work well to finish the verification. After comparing the arguments and flow results, the static and dynamic method has accurate results in bus and line flow. So the desired results have been achieved successfully. It keeps the real and complete points of the original system, so it has a high value in engineering use.