Impact of Increasing the Number of Type-3 Wind Turbines on Stability of Power-system Dynamics

This paper outlines an approach to perform small-signal stability analysis of a power network with conventional synchronous generators and a wind farm composed of Type-3 wind turbines as the number of turbines in the farm is varied. An enabling ingredient to perform this analysis is a dynamic reduced-order aggregate model for a wind farm that preserves the model order and structure of individual wind turbines. This facilitates stability analysis since the number of wind turbines can be varied with ease and small-signal stability of the mixed machine and inverter-interfaced turbines can be examined systematically. Although there is a vast body of literature on small-signal stability of wind farms, penetration level of wind farms is significantly less studied in this context; this paper introduces a systematic approach for such an analysis. Case studies for a modified Kundur two-area system with an integrated wind farm indicate that as the number of wind turbines is increased to a point that the penetration level is approximately 25%, there is a loss of small-signal stability. We validate this with time-domain simulations for the nonlinear system dynamics and also propose a redesign strategy grounded in a system-theoretic analysis of the dynamical models.