Monitoring of Inter-area Oscillations in Power Systems with Renewable Energy Resources Using Prony Method

In this paper, the application of the Prony method for the estimation of dominant inter-area oscillations modes in large power systems is presented. The main goal of this paper is to compare the dominant oscillations modes extracted by the Prony method with those obtained by Eigen-value analysis. In order to achieve that, two testing systems have been designed. The first system is a multimachine system consisting of 22 buses and 10 generators, and the second testing system is built on the same topology but with an integrated Fixed Speed Wind Farm (FSWF). In addition, the impact of the FSWF on interarea oscillation modes will be discussed in this paper. INTRODUCTION ith the recent increases in the number of renewable energy sources in electrical power systems, electricity power regulators now insist that these previously isolated power networks become connected to the main network to form a larger power grids. This will result in long distant power transfers between adjacent power grids. Such power transfers carry the potential risk of low frequency inter-area oscillations in a large power system. Thus, it is critically important to develop reliable and robust methods for monitoring and mitigating potentially dangerous not damped oscillations. To reduce this risk, the identification of the characteristics of the inter-area oscillations, including damping factors and frequency, is an important step before the system operator can apply corrective measures. A conventional method of the identification of oscillation modes is Eigen-value analysis. With the help of Eigenvalues, eigenvectors and participation factors, the system dynamic behaviours can be clearly predicted. The Prony method [1] has been well known for about twenty years; it is capable of extracting the oscillation modes from given signals, such as oscillating frequencies or active powers. Some power companies have utilized the Prony method for the real-time monitoring of power system oscillations in conjunction with new technologies, such as Phasor Measurement Units (PMU). The aim of this research is to compare the oscillation modes obtained from the Eigen-value analysis and Prony method. This will help to provide reliable parameters of power system oscillations for a real time Wide Area Monitoring Protection and Control (WAMPAC). COMPUTER SIMULATIONS 1) Multi-machine testisystem In this part, a test system with 10 synchronous machines, represented in Fig. 1, was analyzed. From the topology of the power system, two areas (A and B) connected over the tie-lines can be easily identified. Under steady-state conditions, approximately 500 MW of active power was transferred over two 1000 km inter-tie lines. Fig.1. The first multi-machine test power system. Under steady-state conditions, the dominant inter-area oscillation modes λ73 and λ74 are calculated by Eigenvalue analysis and presented in Tab. 1. Note that the total number of oscillation modes was 149. Table 1: inter-area oscillation modes for the system from Fig.1. Name Real part Imaginary part Period (s) Frequency (Hz) Damping λ 73 -0.11701 4.719537 1.331314 0.751138 0.11701 λ 74 -0.11701 -4.71954 1.331314 0.751138 0.11701 In order to initialize the inter-area oscillations, a single phase short circuit fault was stimulated on one of the inter-tie lines, lasting from 2-2.1 s. Consequently, the generators in the two areas started to oscillate against each other [2]. Under the above described temporary short circuit, the active power flow over the sound inter-tie line was analyzed using the Prony method. The unknown frequency and damping of the power oscillations estimated by using Prony method are presented in Figs. 2 and 3, which also present the comparisons of the interW C I R E D 20th International Conference on Electricity Distribution Prague, 8-11 June 2009