Real-Time Substep EMT Modeling and Evaluation of Multi-Terminal HVDC Systems

Multi-terminal high-voltage direct current (MTDC) networks require accurate andcomputationally ef􀂉cient real-time electromagnetic transient (EMT) simulation forcontrol and protection validation and hardware-in-the-loop (HIL) applications. Thispaper evaluates mainstep and substep real-time EMT simulation approaches, with anadditional mainstep–substep interface con􀂉guration investigated in a simpli􀂉ed DCcable benchmark. The benchmark compares the real-time approaches to assess theeffects of time-step size and domain interfacing on DC fault transients. The 􀂉ndingsare used to develop real-time models for MTDC con􀂉gurations with two to 􀂉veterminals. A 2 GW, ±525 kV three-terminal North Sea MTDC system is selected fordetailed evaluation, including frequency-dependent DC cable models, metallic returnconductors, and an aggregated offshore wind farm. DC and AC fault responses areassessed, together with the computational and core-allocation requirements of thereal-time models. The results demonstrate the bene􀂉ts of substep modeling for fastDC transients and provide practical guidance for selecting real-time EMT modelingapproaches for MTDC and HIL applications.