Challenges in Microgrids with Medium Voltage Circuit

Hércules A. Oliveira; Luiza H. S. Santos; Luiz A. de S. Ribeiro; José G. de Matos; Lucas de P. A. Pinheiro

doi:10.18618/REP.e202511

Authors

Hércules A. Oliveira Universidade Federal do Maranhão https://orcid.org/0000-0002-7427-5694
Luiza H. S. Santos Universidade Estadual de Campinas (UNICAMP) https://orcid.org/0000-0001-5397-9871
Luiz A. de S. Ribeiro Universidade Federal do Maranhão https://orcid.org/0000-0001-8477-8546
José G. de Matos Universidade Federal do Maranhão https://orcid.org/0000-0001-5340-6459
Lucas de P. A. Pinheiro Institute of Science and Technology Grupo Equatorial https://orcid.org/0000-0002-4641-3703

DOI:

https://doi.org/10.18618/REP.e202511

Keywords:

microgrid, medium voltage, ferroresonance, ungrounded system

Abstract

This paper presents and discusses challenges in microgrids (uGrid) that arise when they operate isolated from the main grid. Specifically, these challenges occur because the system becomes an ungrounded delta configuration, and the microgrid power sources exhibit low short-circuit capacity. The important issues addressed include the failure to detect ground overcurrent during an earth fault event, voltage imbalances recorded by voltage transformers (VTs) connected between phases and earth, and the phenomenon of ferroresonance. These issues directly impact the coordination of electrical protection, component integrity, and synchronization checks between different power sources within the uGrid. Therefore, the Energy Management System (EMS) is tasked with managing protection devices and systematically responding to minimize disruptions, thereby ensuring operational security. This paper examines the protection functions within devices for both operational modes (on-grid and off-grid) and the corresponding decisions implemented as rules within the EMS. Effective coordination between protection devices and management systems ensures a rapid and selective response to faults, thereby enhancing microgrid security and facilitating efficient problem detection and resolution.

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Author Biographies

Hércules A. Oliveira, Universidade Federal do Maranhão

graduated with a bachelor's degree in mechanical engineering from the State University of Maranhão in 2015, Brazil. In the following years, he developed research in the field of automation and control, focusing on power converters, microgrids, and renewable energy sources. In 2017, he received a master's degree in electrical engineering from the Federal University of Maranhão, Brazil. In 2018, he started working on research in the area of ocean energies as a PhD student member of the Brazilian National Institute of Science & Technology of Ocean Energy. In 2019, he was a Graduate Visiting Student at the Schulich School of Engineering at the University of Calgary, Canada, developing research to identify and analyze factors that influence the efficiency of a tidal and wind power plant. In 2023, he received a PhD degree in electrical engineering from the Federal University of Maranhão, Brazil. Currently, he is a postdoctoral student at the Energy Institute of the Federal University of Maranhão and Research and Innovation Coordinator at the Equatorial Group Institute of Science and Technology.

Luiza H. S. Santos, Universidade Estadual de Campinas (UNICAMP)

graduated in Electrical Engineering from the Pontifical Catholic University of Campinas in 2019. During undergraduate studies, participated in four Scientific/Technological Initiation projects, one in the area of current sensors, two in the area of Renewable Energies, and one in Long-Range Wireless Technology (LoRa), all within the Energy Efficiency Research Group. In the master's degree program, in the Department of Systems and Energy of the State University of Campinas, conducted studies on modeling and simulation of microgrids. Currently, she is a doctoral student in the Department of Systems and Energy at the State University of Campinas, participant in the R&D project Microgrids for efficient, reliable and greener energy (MERGE), and member of the Paulista Center for Energy Transition Studies.

Luiz A. de S. Ribeiro, Universidade Federal do Maranhão

received the M.Sc. and Ph.D. degrees from the Federal University of Paraiba, Campina Grande, Brazil, in 1995 and 1998, respectively. During the period 1996–1998 and 2004–2006, he was a Visiting Scholar and Post doctor with the University of Wisconsin, Madison, WI, USA, working on parameter estimation and sensorless control of AC machines. In 2015, he was a Research Guest at Aalborg University, Denmark, working on power converters control for microgrid applications. He is currently a Full Professor with the Department of Electrical Engineering, Federal University of Maranhão, Brazil. His research interests include design and control of power electronics converters, microgrids, and renewable energy. Dr. Ribeiro received two IEEE Energy Conversion Congress and Exposition prize paper awards.

José G. de Matos, Universidade Federal do Maranhão

was born in Brazil in 1957. He received the B.S. and M.S. degrees in electrical engineering from the Federal University of Campina Grande, Paraiba, Brazil, in 1980 and 1986, respectively, and the Ph.D. degree in electrical engineering from the Federal University of Maranhão, São Luís, Brazil, in 2014. Since 1980, he has been a Professor in the Electrical Engineering Department of the Federal University of Maranhão. His research interests include microgrids, control systems, power electronics, and power generation systems based on renewable energy, particularly wind and photovoltaic sources.

Lucas de P. A. Pinheiro, Institute of Science and Technology Grupo Equatorial

received the M.Sc. in Energy and Environment from the Federal University of Maranhão, Brazil in 2019. He worked at Equatorial Energia, managing Research and Development (R&D) and Energy Efficiency (EE) projects. He coordinates Innovation Projects, managing development teams, monitoring delivery of products according to schedules and technically validating the products with the sponsors within electric energy distributors. Currently, he is an Executive at the Institute of Science and Technology Grupo Equatorial.

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