Reduced-Order Modeling and Stability Analysis of Grid-Following and Grid-Forming Hybrid Renewable Energy Plants

The control methods of energy systems can be categorized into grid-following and grid-forming types. The grid-following control method relies on grid synchronization and is prone to stability issues in weak grid conditions. By contrast, the grid-forming control method exhibits synchronous machine characteristics, providing voltage support to the system, but potentially introducing stability risks under strong grid conditions. Constructing a grid-following and grid-forming hybrid renewable energy plant can effectively enhance the system’s support capability and ensure reliable operation. However, the interactions among multiple inverters are complex, and traditional modeling methods are inadequate to meet the modeling requirements for such systems. To effectively address this problem, this paper presents a reduced-order modeling method that simplifies the complex system into a simple system consisting of an equivalent grid-following, an equivalent grid-forming, and grid impedance through frequency decoupling and the aggregation of similar inverters. Furthermore, this study employs both the Nyquist stability criterion and the harmonic characteristic analysis method to elucidate how the capacity ratio between grid-following and grid-forming affects system stability.