Sensitivity analysis for stability region of inverter-based resources with direct method and real-time simulation setup

Inverter-based resources (IBRs) have become indispensable in power systems due to their numerous environmental and operational advantages, which can contribute to enhancing overall grid reliability and resilience. However, due to their stability limitations, IBRs commonly disconnect from the grid when a grid-side disturbance happens. Therefore, inverters’ extensive integration introduces complexities and challenges to power system stability, necessitating the adoption of sophisticated stability assessment tools. One practical approach for assessing large-signal stability involves delineating the system’s stability region. Traditionally, two primary methods have been employed for this purpose: time-domain simulation and direct methods. To tackle the stability assessment of IBRs and sensitivity analysis of stability region, this paper introduces a theoretical direct method based on the sum of squares (SOS) method. It provides a Hardware-in-the-Loop (HIL) simulation to verify the results. The SOS method offers a more precise and less conservative representation of the stability region. Through applying the SOS method, this paper endeavors to establish and investigate the stability region for grid-tied IBR while conducting sensitivity analysis of the inverter responses to grid-side disturbances. This sensitivity analysis specifically delves into the impacts of different load levels and different voltage-loop control parameters on the stability region of the IBR and inverter transit response. In other words, the study develops a theoretical approach using the nonlinear dynamic model and Lyapunov-based stability assessment to understand how a modification in the system can affect the stability region of the IBR and the dynamic response of the inverter for a grid-side fault. The SOS method is applied to construct an accurate Lyapunov function for the system, and the Lyapunov-based stability assessment is used to study system stability under a large disturbance. Besides the numerical sensitivity analysis of inverter dynamic response, the accuracy of the sensitivity analysis is validated through complementary techniques, including time-domain simulations of a grid-tied IBR and high-fidelity HIL simulations using a real-time digital simulation (RTDS) platform. The result proves the outcomes of numerical stability analysis and sensitivity assessment of the IBR using an SOS-based stability analysis.