Unified Transmission-Distribution Coordination for Secure and Economical Frequency Support From Distributed Energy Resources

Utilizing numerous distributed energy resources (DERs) for frequency regulation is a promising pathway to enhance the security and economy of future power systems. However, a fundamental challenge arises from the emergent collective behavior of these resources: their aggregated response, intended to support macro-level system frequency, can jeopardize micro-level local voltage security within distribution networks. To this end, this paper proposes a unified hierarchical framework based on the principle of synergistic co-design. The framework employs a stage-dependent architecture that systematically integrates distinct control strategies for different regulation stages. For security-critical response, it utilizes a novel stage-aware adaptive virtual synchronous generator (VSG) control method with stability formally proven by Lyapunov analysis, while for economic efficiency, it transitions to a distributed control method for cost-optimal restoration. The entire process is underpinned by a proactive voltage security management strategy that enforces micro-level safety. To enable efficient analysis of these complex dynamics, a dual time-scale information interaction mechanism is designed to accelerate the transmission-distribution (T&D) co-simulation process. Simulations on a hybrid transmission-distribution test system validate the framework's effectiveness, demonstrating that the proposed approach enables scalable, secure, and economical frequency support while effectively managing the emergent voltage challenges from collective DER control.