Transient Stability Analysis of a Hybrid Grid-Forming and Grid-Following RES System Considering Multi-Mode Control Switching

TL;DR

This paper analyzes the complex transient stability behavior of hybrid renewable energy systems with grid-forming and grid-following controls, revealing new instability modes and dynamic interactions through theoretical modeling and simulations.

Contribution

It introduces a comprehensive switching system model for hybrid RES, identifying new instability modes and quantifying GFM-RES effects on GFL-RES dynamics.

Findings

Identified two distinct instability modes in hybrid RES systems.

Uncovered the two-dimensional damping characteristics of GFL-RES.

Validated the analysis with high-fidelity electromagnetic transient simulations.

Abstract

The inherent control switching of renewable energy sources (RESs) during intricate transient processes introduces complexity to the dynamic behavior of modern power systems. This paper reveals the dynamic coupling between grid-forming (GFM)/grid-following (GFL)-based RES and dominant instability modes of the hybrid system. First, six control combinations are systematically investigated by pairing the two GFM-RES modes, normal control (NC) and current saturation (CS), with the three GFL-RES modes: normal control, low voltage ride-through (LVRT), and high voltage ride-through (HVRT). Based on switching system theory, the coupled power flow and dynamic motion models are developed considering multi-mode switching characteristics. It is revealed that the hybrid system exhibits two distinct instability modes when the GFM-RES and GFL-RES exceed their P-f and V-f desynchronization boundaries, respectively. The two-dimensional spatiotemporal damping characteristics of GFL-RES induced by GFM-RES are also uncovered for the first time. A novel criterion is proposed to quantify the impact of GFM-RES on GFL-RES dynamics, capturing both its stabilizing and destabilizing effects under different control combinations. High-fidelity electromagnetic transient simulations validate the correctness of the analysis framework.