A dual-layer distributed dispatch framework for frequency-secure unit commitment in integrated Transmission–Distribution networks

The penetration of large-scale renewable energy into power systems poses significant challenges to grid inertia and frequency stability, which have historically been maintained by synchronous generators. To address these issues, this paper proposes a Transient Frequency Security-Constrained Unit Commitment (TFSC-TDUC) model, whose objective is to allocate dispatchable resources across coupled transmission and active distribution networks. By incorporating transient frequency security constraints into the conventional unit commitment framework, the proposed model enhances grid stability by harnessing the frequency regulation capabilities of thermal units, renewable energy sources (RESs), and energy storage systems (ESSs). A coordinated optimization strategy is introduced to incentivize distributed energy resources to participate in auxiliary frequency regulation, thereby improving operational efficiency. To solve the model, the nonlinear frequency constraints are linearized using second-order Taylor expansion and the Big-M method, transforming the problem into a mixed-integer linear programming (MILP) formulation. Furthermore, the Steffensen-accelerated heterogeneous decomposition algorithm (SA-HGD) is employed to enhance computational performance. Case studies demonstrate that the TFSC-TDUC model effectively coordinates resources in coupled transmission and distribution (CTD) networks, alleviating the operational burden on thermal units while improving transient frequency response. The results confirm that our proposed model not only ensures frequency security but also achieves high economic efficiency, enabling reliable grid operation under high renewable energy penetration.