Reduced-Order and Aggregated Modeling of Large-Signal Synchronization Stability for Multi-Converter Systems

During severe grid faults, grid-following converters may become unstable and experience loss of synchronization when complying with requirements for low-voltage ride-through capability. This phenomenon is well described, understood, and modeled for single-converter systems but lacks a modeling framework when extended to multiconverter systems. To fill this gap, this work presents the necessary stability conditions and aggregated reduced-order models for different multiconverter configurations, which can be used to assess the transient synchronization stability of grid-following converters under symmetrical grid faults. The necessary conditions for transient stability and the aggregated models are verified through numerous simulation studies, which verify their high accuracy for large-signal synchronization stability assessment. To that end, the Anholt wind power plant is considered as a case study where the aggregated model is compared to the full operation of a wind farm string containing nine full-order grid-following converter models. High model accuracy is obtained, and the computational burden associated with the proposed model is reduced with a factor of 100 compared with a full-order representation on the tested system. Accordingly, the presented analysis and proposed modeling are attractive as a screening tool and a convenient approach for early-stage fault analysis of system design.