TSO-DSO Operational Planning Coordination through Surrogate Lagrangian Relaxation

Abstract

With the proliferation of distributed energy resources (DERs), located at the Distribution System Operator (DSO) level, uncertainties propagate from Transmission System Operator (TSO) to DSOs and vice versa. Therefore, to enable interoperability, while ensuring higher flexibility and cost-efficiency, both systems need to be efficiently coordinated to operate in sync. Moreover, because of the intermittency of renewable generation, voltages exhibit fluctuations thus necessitating the inclusion of AC power flow. Difficulties behind creating such TSO-DSO coordination include the combinatorial nature of the operational planning problem involved at the transmission level as well as the nonlinearity of AC power flow within both systems. These considerations significantly increase the complexity even under the deterministic setting. In this paper, a deterministic TSO-DSO operational planning coordination problem is considered and a novel decomposition and coordination approach is developed. Within the new method, the problem is decomposed into TSO and DSO subproblems, which are efficiently coordinated by updating Lagrangian multipliers. The nonlinearities at the TSO level caused by AC power flow constraints are resolved through a novel dynamic linearization. Numerical results based on the coordination of 118-bus TSO system with 32 DSO 34-bus systems indicate that both systems benefit from the coordination.<br>