Dynamic Interaction Modeling and Stability Analysis for Grid-Connected Renewable Energy Systems With High Inertia Energy Storage Synchronous Condenser

The high inertia energy storage synchronous condenser (HIESSC), which integrates the doubly-fed machine technology with flywheel energy storage, has recently emerged as a promising means to support both frequency and voltage regulation in renewable energy sources (RESs). Despite its novelty, the impact of the HIESSC on system oscillations and the interactions among the control loops of RES stations remains unclear. This paper examines a grid-connected system comprising the HIESSC and a grid-connected converter with grid-following control (GCC-GFL). Firstly, a single-input-single-output interaction model is developed through equivalent block diagram transformations. By incorporating the grid-side coupling impedance and transfer functions of interacting subsystems, the proposed model reveals how the HIESSC modifies the dynamic characteristics of GCC-GFL through a feedback control perspective. Subsequently, the impact of HIESSC operating modes and operating points on the small-signal stability is analyzed. Finally, the effectiveness of the proposed methods and analyses is validated by the experiments.