A Co-Simulation Framework for Steady-State Analyses of Multiple Droop-Based MTdc Grids in Continental-Scale Systems

Abstract

The growing scale and complexity of planning continental hybrid ac and multi-terminal dc (MTdc) systems require scalable steady-state modeling and analysis approaches not currently available in commercial tools. In particular, widely used planning and commercial power-flow environments typically offer limited support for multiple meshed MTdc grids, and do not natively represent droop-based control and converter current-limiting strategies in a manner that scales to continental studies. As a result, planners often rely on simplified representations that obscure key ac–dc coupling effects. This paper presents a comprehensive multi-fidelity model-conversion framework that enables the efficient transition of MTdc grid models from production cost modeling (PCM) and approximated ac power flow to detailed ac–MTdc power flow for large-scale planning studies. The core of this framework is a scalable co-simulation approach that, for the first time, enables power flow analysis in continental-scale ac–MTdc systems. It seamlessly couples commercial ac solvers with a detailed MTdc grid model that incorporates droop-based control and current-limiting strategies of multiple meshed MTdc grids. Leveraging this capability, an evaluation framework to systematically assess and compare different MTdc power redispatch strategies under ac and dc contingencies is introduced. The proposed framework and algorithm are evaluated using both a combined IEEE 39-bus system with a 3-terminal MTdc grid and a large-scale system integrating the Western and Eastern Interconnections with 11 MTdc grids of varying sizes. The results demonstrate a coherent transition from PCM to detailed ac–MTdc power flow analysis, robust power flow convergence under diverse operating conditions, and enhanced system performance in voltage regulation and transmission line overload mitigation following representative contingencies.