sustainability Article Low Inertia Systems Frequency Variation Reduction with Fine-Tuned Smart Energy Controllers Minas Patsalides * , Christina N. Papadimitriou and Venizelos Efthymiou   Citation: Patsalides, M.; Papadimitriou, C.N.; Efthymiou, V. Low Inertia Systems Frequency Variation Reduction with Fine-Tuned Smart Energy Controllers. Sustainability 2021, 13, 2979. https://doi.org/10.3390/su13052979 Received: 25 December 2020 Accepted: 1 March 2021 Published: 9 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). FOSS Research Centre for Sustainable Energy, University of Cyprus, 1678 Nicosia, Cyprus; papadimitriou.n.christina@ucy.ac.cy (C.N.P.); efthymiou.venizelos@ucy.ac.cy (V.E.) * Correspondence: patsalides.minas@ucy.ac.cy Abstract: The distributed and stochastic nature of Renewable Power Sources is certainly forming considerable challenges for the operation of the power system. Specifically, the stability of the system can be jeopardized when the penetration of inverter-based systems is high. Storage and the proper design of controllers is seen as part of the solution for supporting the future expansion of distributed systems. Thus, control strategies need to be designed to provide the appropriate support to the system and be capable of keeping the variation of the frequency within limits to keep the reliability of the system as high as possible. The main challenge is the appropriate parameterization of these distributed controllers and their coordination under the integrated grid approach in securing the stability of the system at all times. In this paper, a smart energy controller is utilized and incorporated into the projection case study for Cyprus’ real distribution grid for the year 2050 to evaluate its behavior and identify possible weaknesses in its usage. It was found that the parameterization and not only the architecture of such controllers is crucial in coping with the frequency variation and stability problem. From the simulation work and recorded results, it was observed that the smart energy controllers can maintain frequency variation within the desirable range when the parametrization of the controllers is chosen appropriately. This specific observation highlights the need to evaluate and configure the smart controllers while operating in the field, and possibly further research is required to provide the advanced capability to such systems to adjust dynamically during field operation, thereby achieving better response during abnormal conditions. Keywords: frequency variation; low inertia systems; distributed power resources; smart energy controllers; system stability; distribution grid 1. Introduction 1.1. Problem Formulation Renewable energy sources (RES) are considered a valuable energy production technol- ogy solution targeted to benefit the environment by reducing greenhouse gas emissions. The distributed and volatile nature of RES, though, imposes great challenges to grid system operators, while performing the needed integration and management activities [1,2]. To handle these inherent problems, and to harvest huge amounts of renewable energy by successfully integrating low carbon technologies, supporting technologies, including means of storage, are required to facilitate security of supply throughout the day and year. Various research projects and studies are underway to define the best options, setup, mix of technologies and grid structure to cope with the mandatory and unavoidable reforming of the power grid, which will have the ability to host high penetrations of RES [3–6]. A fundamental problem caused by the usage of inverter-based, low-inertia RES sys- tems is their inability to directly support system frequency during the occurrence of abnormal power events due to a lack of additional renewable energy resource. The “re- newable” fuel cannot be increased in any way as is done with diesel and other machines in order to provide additional power input when needed. Sustainability 2021, 13, 2979. https://doi.org/10.3390/su13052979 https://www.mdpi.com/journal/sustainability