Modeling And Stability Simulation Of Distributed Generation System

Vigorous development of distributed generation techniques, especially extensive application of new energy generation techniques, has brought modern power system into a brand new era. Due to the unique dynamic characteristics of the distributed generation sources, grid-connection techniques, and three phase unbalanced network structure, dynamic features of power system have been greatly influenced by the high permeability of distributed energy sources connected to the transmission and distribution grid. This is quite different from traditional bulk power system operation mode,. In this thesis, the main work focuses on the modeling and programming of stability simulation of distributed power generation system. The major achievements are as follows:In the field of modeling techniques, the commonly used typical quasi-steady-state models and control link structures of power electronic devices are summarized in this thesis. A general quasi-steady-state modeling design method is proposed and applied in distributed generation system modeling. The proposed method and model are much beneficial to normalize modeling expression forms of distributed generation system.In the aspect of numerical algorithms, a stability simulation algorithm suitable for distributed generation system is presented in this thesis. In the proposed algorithm, a predict - correction alternate solving implicit integration algorithm is combined with, a numerical differential method to obtain the system Jacobian matrix. With this algorithm, no analytic information of Jacobian matrix elements is required in advance. The Jacobian matrix is acquired directly by numerical calculation based on the original system state equations and algebraic equations. Moreover, this method can automatically take into account the impact of system model structure mutation. Considering the existence of large amounts of discontinuous control links in distributed generation system, this feature makes the proposed method especially advantageous for the development of stability simulation programs for distributed generation system.For the software design and development, a new mesh list data structure is presented based on the sparse storage structure of cross-linked list. The application of this structure can realize highly efficient sparse data storage for DAE system Jacobian during simulation. A Mesh List-Double Layer Algorithm (MLDLA) is developed on the basis of this data structure. The outer layer is designed for explicit integration method, whereas the inner layer is designed for implicit integration method. The consolidated implementation of explicit and implicit integration algorithms is achieved by the double layer structure. For inner layer implicit integration algorithm, the application of mesh list enables a flexible and efficient processing of interface between dynamic components and control devices, as well as the interface between differential equations and algebraic equations of the DAE system. The DAE system block Jacobian matrix can be assembled arbitrarily based on modularized design. This provides a convenient solution for the addition and update of new components and new models.Furthermore, the system object-oriented design and analysis method is investigated in this thesis to carry out stability simulation of distributed generation system. The double-layer AC-DC bus-tree structure for grouping elements in distributed generation system is presented to describe grid-connection system. The interface of double-layer AC-DC bus-tree is similar to generator and its control unit in traditional power grid. It has"plug and play"feature. In the following part, design methods for modeling class and functional class are illustrated, as well as structure and function of major classes.In the end, simulation results for test cases are given to validate the correctness of the modeling and algorithm for stability simulation of distributed generation system.