Study Of Electromagnetic Transients Simulation And Equivalence Of Power Systems

With the development of the power system automation and the popularization of AC/DC hybrid transmission technology, there are more and more kinds of power electronic equipments in systems, which leads to more and more scenes and tasks needing electromagnetic transient simulation calculation and analysis. It is time-consuming to performe electromagnetic transient simulation for the actual large-scale systems. To accelerate the speed of simulation, one approach is to transform the large system into small ones by simplification or equivalence processing. So, the network equivalence process is an important issue in electromagnetic transient research. To focus on the deficit and problem of simulation and equivalent methods in electromagnetic transient, a thoroughly exploration and study have been done in this thesis and many satisfactory achievements are obtained. The main achievements and research contents are listed as followed.Firstly, a parasitic switch model and a new interpolation algorithm is presented, which considers the action of multiple switches. The new parasitic switch model is obtained by combining the switch element with its adjacent series component,and unified difference processing of the electromagnetic transient model of the whole component. By this model, it might reduce the node number in the system, and speed up the simulation speed. After finding the accurate switching time by interpolation technology first, and then using the trying and testing integral strategy of backward Euler to process the multiple switches, in addition to extrapolation and back-push technology of backward Euler integral with 1% step length, the numerical oscillation and non-characteristic harmonics could be eliminated by the new interpolation considering multiple switches. The results of the samples demonstrate the effectiveness and validity of above methods.Then, a new frequency-dependent equivalent method of external systems for power system electromagnetic transient simulation is presented in the paper, which reduces large system into small ones and to accelerate electromagnetic transient simulation calculation speed. In the method, an effective algorithm is designed to directly transfer the port admittance determinant of mixing matrix of external system into admittance polynomial function; and the step by step strategy for large system is put forward, which further reduces the calculation quantities and speed up the solution procedure of the port admittance polynomial function of practical large system. Moreover, the study of root characteristics of admittance transfer function of two-port network is performed and the proposition is achieved; based on the proposition and the residue theorem, the polynomial function is further transferred into admittance rational function, and a simple equivalent system for external system is obtained by the rational function. The computational complexity of the step by step equivalence method is about o ( ?? n / n p?? ?T) ( ?? ?? is the upper integral, n is the total node number of external system, n p is the node number of single step equivalent network, T is single step equivalent time), which indicates that the computational complexity of the method has nearly linear relationship with the node number of external system, and has a faster computation speed than others. Since the mixing matrix of external system includes all the information of external system, therefore, port admittance rational function can reflect its full frequency characteristic and the equivalent network based on it has high equivalent precision; besides, the rational function is gained for the external system without resource, which equals to be stable passive network, thus, there is no unstable pole.The new simulation and equivalent methods for electromagnetic transient simulation presented in this thesis, promote the development of simulation and equivalent technology study. The methods proposed in this thesis and the software developed based on it own the potential to be applied for practical power system application.