Systematic Decoupling Grid-Forming Control for Utility-Scale Inverter-Based Distributed Energy Resources in Weak Distribution Grids

Abstract

Existing grid-forming inverter control schemes for distributed energy resources (DERs) primarily rely on active power (P)-frequency (f) and reactive power (Q)-voltage (V) droop mechanisms that are tailored for highly inductive transmission grids. However, in weak distribution grids where P and Q are highly coupled due to their resistive network characteristics, these control schemes cannot provide independent and accurate f and V regulation. This will further deteriorate the dynamic and stability performance, potentially resulting in inverter and load tripping during disturbances. To address this challenge, this paper proposes an innovative decoupling grid-forming control scheme, which is designed based on a systematic perspective that considers the inherent coupling characteristic of the entire distribution grid. The small-signal stability of the proposed controller is analyzed by varying controller parameters and the grid strength. The effectiveness of this controller is comprehensively verified using both MATLAB and OPAL-RT platforms by comparing it with existing grid-forming control strategies. The results show that the proposed controller can effectively decouple P and Q regulation in weak distribution grids. It enables DERs to provide independent, accurate, and autonomous f and V regulation, thus improving grid stability and dynamics. The proposed control strategy is cost-effective, communication-free, and can be easily commercialized due to its straightforward and robust circuit design.