Method to Quantify Modal Interactions Between Converter Interfaced Generators and Synchronous Generators

The aim of this paper is to quantify the interactions between the oscillation modes of Converter Interfaced Generators (CIG) and electromechanical oscillation modes of Synchronous Generators (SGs) within the realm of small-signal stability. It is difficult to quantify the modal interactions using the existing analysis such as mode sensitivity, mode loci and participation factors. This paper proposes an extension to the eigenvalue sensitivity analysis in order to determine the interactions between modes and the impacts of the interactions on the system stability. Interaction coefficients are proposed to quantify the interactions between the modes. A modified IEEE 39-bus system with CIGs is considered to carry out the analysis using proposed interaction coefficients. In this paper, results are presented considering CIG based renewable energy penetration levels of 50-70%. It is observed that the interactions between the oscillation modes of CIGs and electromechanical modes of SGs result in increased participation of SGs' states in CIG modes. This increased participation of SG states in the CIG modes results in reduced damping of oscillations in SG states. Possible applications of the proposed interaction coefficients are also identified. The impacts of PLL parameters on the interactions among the oscillation modes are investigated using proposed interaction coefficients. Results demonstrate that the impact of PLL on interactions increases with increasing CIG penetration.