Unified Modeling and Analysis of Dynamic Power Coupling for Grid-forming Converters

Grid-forming converters, taking droop-controlled converters and virtual synchronous generators (VSGs) as typical examples, have shown great promise as the interfaces between renewable energy sources and the future power-electronics-based power system. However, the coupling between active and reactive power will adversely affect the dynamic performance and stability of grid-forming converters. In order to facilitate quantitatively analyzing and assessing the power coupling characteristics of various types of grid-forming strategies, this article develops a unified dynamic power coupling model based on a first amplification coefficient array and a relative gain array in the frequency domain. Then, by using the established unified model, a comprehensive analysis of dynamic power coupling properties for typical VSG control and droop control is presented, which reveals that droop control is helpful in weakening power coupling while VSG control is prone to amplify the coupling. Moreover, the influences of the pivotal control parameters in droop and VSG controllers on power coupling characteristics are discussed in detail, which can provide novel supplementary guidelines for parameter design of droop and VSG controllers. Finally, the experimental results verify the correctness of theoretical modeling and analysis.