Application of modal estimation techniques for small signal stability assessment in distribution systems considering measurement noise

The increase of distributed generation in the global scenario has motivated the study of the electromechanical oscillation phenomenon in distribution systems with load imbalance, an intrinsic characteristic of this type of system. In this paper, after showing that typical linearization procedures cannot be applied to the assessment of the small-signal stability of unbalanced distributed generation systems, this assessment is done with the application of a modal estimation technique: the Prony method. This approach enables the calculation of oscillation frequencies and damping ratios under unbalanced conditions, as earlier works from the authors have shown. However, under realistic conditions, measurement noise patterns with different spectra may degrade the results of the proposed application. The main contribution of this paper is the evaluation of the impact of noise over the small-signal stability assessment technique proposed by the authors for unbalanced distribution generation systems, aiming at a better suited technique for practical applications. The results show that, while frequency remains mostly unaffected by the presence of noise, the identification of the damping ratio can be significantly influenced by this factor.