**Preface to "Advancements in Real-Time Simulation of Power and Energy Systems"**

Modern power and energy systems are characterized by the wide integration of distributed generation, storage and electric vehicles, adoption of ICT solutions, and interconnection of different energy carriers and consumer engagement, posing new challenges and creating new opportunities. Advanced testing and validation methods are needed to efficiently validate power equipment and controls in the contemporary complex environment and support the transition to a cleaner and sustainable energy system. Real-time hardware-in-the-loop (HIL) simulation has proven to be an effective method for validating and de-risking power system equipment in highly realistic, flexible, and repeatable conditions. Controller hardware-in-the-loop (CHIL) and power hardware-in-the-loop (PHIL) are the two main HIL simulation methods used in industry and academia that contribute to system-level testing enhancement by exploiting the flexibility of digital simulations in testing actual controllers and power equipment. This Special Issue aims to address recent advances in real-time HIL simulation in several domains (also in new and promising areas), including technique improvements, to promote its wider use.

The Special Issue is composed of 14 papers submitted from Europe, North America, and Asia, covering the following areas:


K. Sidwall et al. summarize various recent advancements in real-time digital simulation, which have been enabled by the growth in high-performance processing space and the emerging availability of high-end processors for embedded designs. These include predictive switching of power electronic converters, streaming GOOSE and Sampled Values (IEC 61850-90-5), FPGA-based data streaming, and improved models of synchronous machines, transformers, and transmission lines. The second paper by M. Mirz et al. describes recent improvements to the open-source real-time simulator DPsim to study important use cases that involve grid-connected power electronics. It is shown that dynamic phasors, which result from shifted frequency analysis, allow the user to efficiently combine the characteristics of conventional phasor and electromagnetic transient simulation. A real-time hybrid simulator for dynamic performance testing of power electronic replica controllers in large power systems was developed and tested by J. Song et al. The hybrid simulator is a co-simulation tool that synthesizes a real-time simulator with a transient stability program to perform real-time dynamic simulation of a large power system. F. D'Agostino et al. illustrate in detail the development of a multiphysics real-time simulation framework, able to mimic the behavior of a DC electric ship equipped with electric propulsion, rotating generators, and battery energy storage systems. This section is concluded by L. Estrada et al. that present a systematic methodology for HIL simulation of power converters using LabVIEW software and FPGA.

CHIL simulation is addressed in the next set of papers. D. Sodin et al. developed and tested an under-frequency load shedding (UFLS) protection scheme in a CHIL setup. The under-frequency technology was implemented in an intelligent electronic device (IED) and it was shown that locally measured RoCoF can be effectively used for bringing a high level of flexibility to a system-wide scheme. J. Song et al. present industrial experiences of the first thyristor controlled series compensator (TCSC) replica controller installed in Korea (in 2019) through a review of its configuration, test platform, and practical application. The control performance was accurately verified under the entire Korean power system. L. Pellegrino et al. introduce the Joint Test Facility for Smart Energy Networks with Distributed Energy Resources (JaNDER) that allows users to exchange data in real time between two or more laboratory infrastructures and create a virtual infrastructure combining resources installed in different locations. Remote CHIL test cases are reported.

PHIL simulation is addressed at the last set of papers. A comparison of DER voltage regulation technologies using real-time simulations is performed by A. Summers et al. A novel state estimation-based particle swarm optimization for distribution voltage regulation was developed and tested in a PHIL setup. M. Barragan-Villarejo et al. propose a power system hardware-in-the-loop ´ (PSHIL) concept, which widens the focus from device-oriented to system-oriented testing in order to evaluate, in a holistic way, the impact of a given technology on the power system, considering all of its power and control components. Geographically distributed PHIL tests by re-purposing existing grid-forming converters as a power interface and using the internet are reported by S. Vogel et al. M. Syed et al. present a non-intrusive add-on controller for DER inverters and establish its practical real-world relevance via a rigorous performance evaluation utilizing a high-fidelity HIL test bed. B. Guo et al. developed a variable speed hydro-electric plant PHIL setup, which is dedicated to different hydraulic operation scheme testing and control validation, while using reduced-scale models.

Finally, J. Montoya and members of the Smart Grid International Research Facility Network (SIRFN) present a comprehensive review of methods, test procedures, studies, and experiences by employing advanced real-time laboratory techniques for the validation of a range of research and development prototypes and novel power system solutions.

> **Panos Kotsampopoulos , Md Omar Faruque** *Editors*
