Normal Mode Analysis of Inter-Area Oscillations

In this paper, a linear normal mode-based formulation for analyzing inter-area oscillations is presented. The method is based on the property of invariance of the modal subspaces and can be used to represent complex power system modal behavior by a set of uncoupled linear oscillators. Using the theory of modal subspaces, a new approach is outlined, for determining the linear normal modes (NMs) of motion of a general n-degree of freedom linear system. Within this framework, techniques to characterize modal behavior in terms of the linear NMs are explored, and procedures to compute the speed and displacement of the normal modes are proposed. A mechanical interpretation of NMs in terms of velocities and displacements is also provided. Numerical and symbolic examples are presented to illustrate the effectiveness and applicability of the proposed analysis technique. Specifically, we demonstrate and discuss the use of normal mode analysis as a basis for identifying modal parameters, including natural frequencies and damping ratios of general, linear systems with n degrees of freedom