A New Eigenvalue Analysis Method for Large-Scale Power Systems Including Digital Controllers

Eigenanalysis methodologies for large-scale power systems are considered to be already well-established and many methods have been proposed since the middle of the 1970s. The features of these methods are, 1) to utilize the sparsity techniques, 2) to obtain specific set of eigenvalues, 3) to have numerical robustness, etc. On the other hand, recently digital excitation controllers have been aggressively introduced in power systems and a method that can grasp the characteristics of power systems including them is strongly desired. Eigenvalue methods are suitable for identifying fundamental characteristics of power systems by using eigenvalues and eigenvectors obtained from a state matrix linearized around an equilibrium point. A digital control system includes 0-th order hold or 0-th order delay function with sampling period T, these elements can be drscribed as difference equations whose characteristic is different from differential equations. Those elements make structure of the state matrix dense, therefore, it is difficult to apply conventional sparsity technique to the state equation including difference equations. An eigenvalue method for large scale-power systems including digital controllers has not been established yet due to such reasons. In this paper, the authors propose an efficient eigenvalue method which can deal with large-scale power systems including digital controllers by using newly developed sparsity technique. To confirm the effectiveness of the proposed method, test calculations were carried out by using a 16 generator and a 64 generator systems. The results show that the proposed method was able to obtain eigenvalues with sufficient accuracy and high speed.