Frequency dependent network equivalents for electromagnetic transient studies

In electromagnetic transient studies, only a small part of an AC power syst em can be modeled in detail. The remaining parts of the system should be re duced to equivalent model. Different methods were developed to generate fre quency dependent network equivalents. This paper presents a novel approach for obtaining network equivalents for ac power systems using the QZ algorit hm. The proposed method obtains accurate resonant frequencies directly from the system equations to be used in finding the network equivalent paramete rs. Also, the proposed method is a good tool to predict the system response . The use of the QZ algorithm in the creation of the network equivalent mod e! gives the following advantages: 1. Improved accuracy: as compared to the direct frequency response method. 2. Less complexity: because it obtains the minima and maxima frequencies di rectly from the system equations. 3. Reliable prediction: it gives the complete information about the behavio r of the test system and its peaks and troughs before calculating its frequ ency response. 4. Good evaluation of network's resistance: the proposed method determines the resistors of the network equivalent model as the real part of the imped ance function magnitude at the minima frequency points. In this article, a general algorithm is developed to determine the frequenc y dependent network equivalent model parameters for any given system. Final ly a four-bus test system is introduced to show the accuracy and the valida tion of the proposed method. For simplicity and convenience a comparison be tween the direct frequency response method and the proposed method, a two-b us system, is also studied in this work. Good results were obtained for net work equivalent models for both the frequency and time domains. (C) 1999 El sevier Science Ltd. All rights reserved.