Reactive Power Characteristics and FRT Strategy for Grid-Forming Converters With Virtual Impedance-Based Current Limiting

Abstract

Grid-forming (GFM) converter is a promising interface for integrating renewable energy sources. During grid faults, GFM converters inherently contribute to reactive power support, while current limiting can significantly affect the reactive power characteristics and pose challenges for grid code compliance. In this study, the impacts of virtual impedance (VI)-based current limiting on reactive power characteristics of GFM control are investigated. It reveals that the VI may cause phase offset and deterioration of the natural and instant reactive power support capability, and the subsequent reactive power response faces a coupling with the active power control due to the current magnitude limitation. Leveraging these characteristics, an enhanced fault ride-through (FRT) strategy is proposed. Firstly, the VI impedance angle is recommended to match the equivalent connection impedance, which inherits the natural power support capability of GFM converters and improves instant voltage support capability. Secondly, an FRT strategy based on dynamic active power limitation is proposed for fulfilling the grid code and enhancing the subsequent reactive power support. The effectiveness of the proposed strategy is validated through comparative time-domain simulations.