Transmission-Distribution Co-Simulation: Model Validation with Standalone Simulation

The ever-growing complexity of power grid is increasing the interactions between its different integrated subsystems and rendering the traditional analysis tools insufficient for high-fidelity studies. Specifically, the integration of distributed energy resources (DERs) is increasing the interactions between transmission and distribution (T&D) systems. The traditional decoupled methods for T&D system analysis cannot capture the interactions between the T&D systems thus, calling for new methods in integrated T&D analysis. Lately, several co-simulation frameworks have been developed to model T&D interactions by exchanging the power flow solutions at the point of common coupling (PCC). The existing frameworks, however, make some assumptions to reduce the complexity of co-simulation when solving a large-scale coupled T&D system. The assumptions employed to solve and couple the two models characterize the fidelity of the co-simulation platform. Therefore, it is imperative to validate the results obtained from co-simulation approach against a standalone unified model of the T&D system. This paper aims at validating an iteratively coupled T&D co-simulation approach against the standalone model in DIgSilent software. Test cases are generated using IEEE-9 node transmission system coupled with IEEE-13 bus distribution system. It is demonstrated that the proposed co-simulation tool closely approximates the power flow quantities to those obtained from the corresponding standalone model.