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This paper develops a real-time (RT) transmission and distribution (T&D) co-simulation platform for testing distributed energy resources management system (DERMS) algorithms. The platform consists of a transmission system modeled within a real-time transient-stability type environment interfaced to an active distribution network modeled within a fundamental frequency phasor-domain platform. The data exchange and time synchronization between the T&D models has been established via MQTT communication protocol, enabling the platform to communicate with a large number of DER models in real-time. The developed platform is generic in the sense that it can integrate an arbitrarily sized transient stability-type model of a transmission system with an arbitrarily sized fundamental frequency phasor-domain model of a distribution system. The platform does not impose an inherent limit on the size of the T&D models, and the size is limited by the computational capability of the simulation computer. This feature enables utilizing the platform for simulation studies of large-scale T&D systems. Furthermore, the developed platform enables both off-line and real-time simulations, extending its application from off-line planning-type studies to real-time operation-type and hardware-in-the-loop (HIL) studies. The paper demonstrates the application of the developed platform in a large-scale case study utilizing behind-the-meter (BTM) DERs to provide grid services when controlled by a DERMS. By including the propagation of dynamics between the simulation domains, realistic DER models, and typical communication protocols that are used in the field, the proposed platform enables the testing of DERMS algorithms in a close to real environment, replicating a wide range of power system phenomena that highlight the impact of a DERMS in an actual power system.

Modeling large-scale electric power systems for electromagnetic transient (EMT) studies in real-time simulations is challenging due to factors such as real-time constraints, computational workload, extensive modeling efforts, and model accuracy. Developing a detailed and accurate EMT model of large-scale modern transmission networks is time-consuming and requires advanced computational capabilities. This paper proposes a Plug-and-Play (PnP) regional modeling approach to address the abovementioned challenges. An entire power grid is split into multiple regions, and each region is modeled with the PnP feature. A multi-regional model can be easily formed by merging multiple regional models due to the PnP capability. The advantage of PnP regional models is that it enhances the computational efficiency of an EMT simulation. Regional EMT models enable the accurate representation of a portion of the power system, allowing for accelerated simulation of local EMT models while providing a Thevenin equivalent of the rest of the system. A comprehensive procedure to develop and maintain the PnP regional models will be presented in this paper. A case study of the New York State (NYS) power grid is taken into consideration to demonstrate how utilities can utilize the proposed approach to develop their power grid models for EMT studies. A detailed explanation of using the PnP feature to form a multi-regional model is presented to provide a solid perspective on the application of developed PnP regional models. Furthermore, a code-based automated process is developed to maintain the real-time models up-to-date, which involves automatically processing input models and generating a real-time model accommodating all the changes. The significance of this study is to provide a guideline for handling large-scale power system modeling and deliver insight into the industry to the researcher.