The rapid deployment of offshore wind energy is essential for decarbonizing the power grid and achieving net-zero emission targets by 2050. However, integrating large-scale offshore wind farms (OWFs) into AC power networks presents significant stability and interoperability challenges. These challenges arise from the increasing complexity of offshore systems, which are characterized by the widespread use of power electronic converters, long AC transmission distances, and multi-vendor component interactions. Such conditions can degrade grid dynamic performance and lead to undesirable oscillatory instabilities. Existing stability assessment methods often rely on centralized models and detailed global system information, complicating compliance testing and limiting scalability. This underscores the critical need for decentralized, impedance-based stability criteria to support secure and reliable OWF integration.

To address these challenges, this paper proposes a novel framework for the decentralized and scalable integration of OWFs into AC networks, based on frequency-domain stability analysis. The key idea is to formulate impedance-based stability criteria that can be verified locally at each wind turbine or cluster connection point, thereby ensuring system-wide small-signal stability. This is achieved by modelling wind turbine and network elements as feedback-interconnected subsystems and applying a decentralized Nyquist-type condition. This approach eliminates the need for global system models, making it well-suited for multi-vendor environments and facilitating compliance assessment.

The main contribution of this work lies in the decentralized nature of the stability framework. In contrast to centralized approaches that necessitate full-network models and extensive EMT simulations, the proposed method enables local stability assessment using only nearby subsystem dynamics. Moreover, the frequency-domain formulation allows for the evaluation of black-box models, effectively addressing intellectual property concerns in multi-vendor systems. The framework enhances existing grid codes by improving plug-and-play capability and interoperability, thereby enabling scalable integration of offshore wind assets while preserving system-wide stability.

The effectiveness of the framework is demonstrated through a case study involving the integration of multi-vendor OWFs into an AC grid. A high-order model of a grid-forming permanent magnet synchronous generator (PMSG)-based wind farm is developed, capturing both mechanical and electrical dynamics. The study focuses on scenarios where additional wind farms or subsystems are added to an IEEE 9-bus network. The proposed decentralized criteria are applied locally to assess subsystem stability, with results validated through time-domain simulations in MATLAB/Simscape.