Techno-economic assessment of a low-frequency AC transmission interconnection for an offshore wind farm in Colombia

Cristian Bernal; Valentina Fragozo; Iván Ortega; Rafael Castillo-Sierra; Mauricio Restrepo; Juan Diego Pulgarín Rivera

doi:10.32397/tesea.vol7.n1.970

Authors

Cristian Bernal Universidad del Norte , Universidad del Norte , Universidad del Norte https://orcid.org/0009-0005-9291-2254
Valentina Fragozo Universidad del Norte , Universidad del Norte , Universidad del Norte https://orcid.org/0009-0008-7747-004X
Iván Ortega Universidad del Norte , Universidad del Norte , Universidad del Norte https://orcid.org/0009-0009-3708-6219
Rafael Castillo-Sierra Universidad del Norte , Universidad del Norte , Universidad del Norte https://orcid.org/0000-0002-2648-4096
Mauricio Restrepo Universidad del Norte , Universidad del Norte , Universidad del Norte https://orcid.org/0000-0002-2856-4559
Juan Diego Pulgarín Rivera Francisco José de Caldas District University https://orcid.org/0000-0003-2326-7907

DOI:

https://doi.org/10.32397/tesea.vol7.n1.970

Keywords:

Low-Frequency AC Transmission (LFAC), Modular Multilevel Converter (MMC), Offshore Wind Integration, Renewable Energy Grid Connection, Techno-Economic Analysis

Abstract

Colombia’s Caribbean coast has substantial offshore wind potential but lacks dedicated transmission infrastructure. Although high-voltage AC (HVAC) and high-voltage DC (HVDC) are established solutions, low-frequency AC (LFAC)—the transmission of power at frequencies below the standard 50 or 60 Hz—offers a cost-effective alternative for medium-distance applications. This study assesses an LFAC system to connect a 960 MW offshore wind farm to the national 60 Hz grid under Colombian regulatory and geographic conditions. The proposed LFAC link operates at 20 Hz and includes a 75 km submarine cable, a 34 km overhead line, and a back-to-back modular multilevel converter working as a frequency conversion station. The design meets national limits on voltage regulation and unbalance, and considers efficiency, shunt currents, and transfer capability. Performance was validated using MATLAB/Simulink simulations under variable load. The economic analysis compares capital expenditure (CAPEX) and loss-related costs with HVAC and HVDC. The system achieved over 93% efficiency and complied with all voltage standards. Compared to 60 Hz HVAC, the 20 Hz LFAC enabled roughly 200% more transfer capacity and reduced shunt currents by 66%, improving stability. LFAC’s CAPEX was 9.4% higher than HVAC but 8.1% lower than HVDC. LFAC is technically and economically viable for offshore wind integration in Colombia, bridging HVAC’s reactive limitations and HVDC’s high costs, and is scalable for similar renewable projects worldwide.

Downloads

Download data is not yet available.

References

Congreso de Colombia. Ley 1715 de 2014, 2014.

The Renewables Consulting Group and ERM. Hoja de ruta para el despliegue de la energía eólica costa afuera en colombia. Technical report, Ministerio de Minas y Energía, Colombia, 2022. Prepared in collaboration with the World Bank.

X. Xiang, M. M. C. Merlin, and T. C. Green. Cost analysis and comparison of hvac, lfac and hvdc for offshore wind power connection. In 12th IET International Conference on AC and DC Power Transmission (ACDC 2016), pages 1–6, 2016.

Yongqing Meng, Shuhao Yan, Kang Wu, Lianhui Ning, Xuan Li, Xiuli Wang, and Xifan Wang. Comparative economic analysis of low frequency ac transmission system for the integration of large offshore wind farms. Renewable Energy, 179:1955–1968, 2021.

Jonathan Ruddy, Ronan Meere, and Terence O’Donnell. Low frequency ac transmission for offshore wind power: A review. Renewable and Sustainable Energy Reviews, 56:75–86, 2016.

P. B. Wyllie, Y. Tang, L. Ran, T. Yang, and J. Yu. Low frequency ac transmission - elements of a design for wind farm connection. In 11th IET International Conference on AC and DC Power Transmission, pages 1–5, 2015.

Sakis A. P. Meliopoulos, Dionysios Aliprantis, Yongnam Cho, Dongbo Zhao, Anupama Keeli, and Hao Chen. Low frequency transmission: Final project report. Technical Report 12-28, Power Systems Engineering Research Center (PSERC), Georgia Institute of Technology and Iowa State University, October 2012. PSERC Publication 12-28.

Xin Xiang, Shiyuan Fan, Yunjie Gu, Wenlong Ming, Jianzhong Wu, Wuhua Li, Xiangning He, and Timothy C. Green. Comparison of cost-effective distances for lfac with hvac and hvdc in their connections for offshore and remote onshore wind energy. CSEE Journal of Power and Energy Systems, 7(5):954–975, 2021.

Byeonghyeon An, Jeongsik Oh, and Taesik Park. Economic analysis of critical distance based on frequency in low frequency ac for offshore wind farms. IEEE Access, pages 1–1, 2025.

C Nguyen Mau, K Rudion, A Orths, PB Eriksen, H Abildgaard, and ZA Styczynski. Grid connection of offshore wind farm based dfig with low frequency ac transmission system. In 2012 IEEE power and energy society general meeting, pages 1–7. IEEE, 2012.

Nan Qin, Shi You, Zhao Xu, and Vladislav Akhmatov. Offshore Wind Farm Connection with Low Frequency AC Transmission Technology. In 2009 IEEE Power & Energy Society General Meeting, pages 1–8. IEEE, 2009.

I Erlich, F Shewarega, H Wrede, and W Fischer. Low frequency AC for offshore wind power transmission – prospects and challenges. In -, pages 1–7. IET, 2015.

Xin Xiang, Shiyuan Fan, Yunjie Gu, Wenlong Ming, Jianzhong Wu, Wuhua Li, Xiangning He, and Timothy Green. Comparison of cost-effective distances for LFAC with HVAC and HVDC in their connections for offshore and remote onshore wind energy. CSEE JOURNAL OF POWER AND ENERGY SYSTEMS, 7(5):1–22, 2021.

Ming Hu, Shuhong Xie, Jianmin Zhang, and Zhijin Ma. Desing selection of dc and ac submarine power cable for offshore wind mill. In 2014 China International Conference on Electricity Distribution (CICED), pages 1675–1679, 2014.

CIGRÉ. Power cable rating examples for calculation tool verification. Technical Brochure 880, CIGRÉ, 2022. Case Study 8, 220kV 3-core submarine export cable.

International Electrotechnical Commission. IEC 60287-1-1: Electric cables - Calculation of the current rating - Part 1-1: Current rating equations and calculation of losses, 2006. Norma para evaluación térmica de cables XLPE.

AIEE Committee. Soil thermal characteristics in relation to underground power cables aiee committee report. Transactions of the American Institute of Electrical Engineers. Part III: Power Apparatus and Systems, 79(3):792–844, 1960.

Copernicus marine service - ocean data portal. https://data.marine.copernicus.eu, 2025. Accessed: 2025-05-16.

Lionel Carter, Douglas Burnett, and Tara Davenport. The relationship between submarine cables and the marine environment. In Douglas R. Burnett, Lionel Carter, and Tara Davenport, editors, Submarine Cables: The Handbook of Law and Policy, chapter 7, pages XXX–XXX. Brill Nijhoff, Leiden, The Netherlands, 2020.

International Cable Protection Committee. ICPC Recommendation No. 10: Industry Standards for Consultation, Coordination, and Spatial Separation. Technical Recommendation, n.d. Recommends parallel submarine cables maintain a separation distance of the lesser of 3 times the depth of water, or 2 times with agreement.

T. Kvarts, A. C. Garolera, Z. Huang, and O. Thyrvin. Sequence impedance of submarine cables. In CIGRÉ Session, number 10693, Paris, France, 2022. CIGRÉ.

Electric Power Research Institute. EPRI AC Transmission Line Reference Book—200 kV and Above, 2005.

IEEE Power Engineering Society. IEEE Std-738-2006: Standard for Calculating the Current-Temperature Relationship of Bare Overhead Conductors, 2007. IEEE Standard.

Ministerio de Minas y Energía de Colombia. RETIE 2024: Reglamento Técnico de Instalaciones Eléctricas, 2024. Resolución 40117 del 2 de abril de 2024.

UNIVERSIDAD NACIONAL DE COLOMBIA. Metodología para Selección de Cable de Guarda en Líneas Aéreas de Alta Tensión, 2021.

International Electrotechnical Commission. Iec 60071: International standard — insulation co-ordination, 2019.

International Electrotechnical Commission. Iec 60038: International standard — iec standard voltages, 2009.

International Electrotechnical Commission. Iec 60099: International standard — surge arresters, 1991.

International Electrotechnical Commission. Iec 60815: International standard — selection and dimensioning of high-voltage insulators intended for service in polluted conditions, 2013.

R. Marquardt and A. Lesnicar. A new modular voltage source inverter topology. Conf. Rec. EPE 2003, 2003.

Rafael Castillo-Sierra and Jinia Roy. Active power decoupling to minimize submodule capacitance and circulating currents in modular multilevel converters. In 2024 IEEE Energy Conversion Congress and Exposition (ECCE), pages 57–64, 2024.

David Sehloff and Line A. Roald. Low frequency ac transmission upgrades with optimal frequency selection. IEEE Transactions on Power Systems, 37(2):1437–1448, 2022.

David Sehloff and Line Roald. Steady state modeling for variable frequency ac power flow. In 2020 52nd North American Power Symposium (NAPS), pages 1–6, 2021.

Ronan Meere, Jonathan Ruddy, Paul McNamara, and Terence O’Donnell. Variable ac transmission frequencies for offshore wind farm interconnection. Renewable Energy, 103:321–332, 2017.

Byeonghyeon An, Junsoo Che, Taehun Kim, and Taesik Park. Selection of an optimal frequency for offshore wind farms. Energies, 17(10), 2024.

Peng Qiu, Xiaojun Ni, Feng Xu, Chengyu Lu, Kaijun Wang, and Wulue Pan. Optimal transmission frequency of low frequency ac system for offshore wind farm integration. In 2021 International Conference on Power System Technology (POWERCON), pages 1556–1560, 2021.

Rafael Castillo-Sierra and Giri Venkataramanan. A comparative evaluation of power converter circuits to increase the power transfer capability of high voltage transmission lines. In 2020 52nd North American Power Symposium (NAPS), pages 1–6, 2021.

Rafael Castillo-Sierra, Giri Venkataramanan, and Dionisio Ramirez. Control design guidelines for current-mode modular multilevel matrix converters based on dynamic modeling and stability analysis. In 2025 IEEE Workshop on Power Electronics and Power Quality Applications (PEPQA), pages 1–8, 2025.

Rafael Castillo-Sierra, Giri Venkataramanan, and Dionisio Ramirez. Small-signal stability analysis of droop-controlled point-to-point low-frequency ac transmission lines. In 2023 IEEE Energy Conversion Congress and Exposition (ECCE), pages 2301–2308, Nashville, TN, USA, 2023. IEEE.

CREG. Resolución creg 025 de 1995: Por la cual se establece el reglamento de calidad del servicio de energía eléctrica, 1995.

ICONTEC. NTC 5001: Código Eléctrico Colombiano, 2011. Norma Técnica Colombiana.

ABB Semiconductors Ltd. Reverse Conducting Integrated Gate-Commutated Thyristor (RC-IGCT) 5SHX 36L4521 – Preliminary Data Sheet. ABB Switzerland Ltd, Semiconductors, Lenzburg, Switzerland, 2020. Preliminary data sheet.

Jovana Dakica, Marc Cheah-Manea, Oriol Gomis-Bellmunt, and Eduardo Prieto-Araujo. Low frequency ac transmission systems for offshore wind power plants: Design, optimization and comparison to hvac and hvdc. CITCEA-UPC, Department of Electrical Engineering, Universitat Politècnica de Catalunya, 2021. Technical report.

Jian Liu, Dong Dong, and Di Zhang. A hybrid modular multilevel converter family with higher power density and efficiency. IEEE Transactions on Power Electronics, 36(8):9001–9014, 2021.

Government of India, Ministry of Power, and MNRE. India roadmap for offshore wind power evacuation and grid integration. Technical report, Accelerating Smart Power and Renewable Energy (ASPIRE) Programme, 2023. Offshore wind transmission planning and evacuation framework study.

Nicolo Stevanato, Valeria Baiocco, and Emanuela Colombo. Calliope africa: Modeling the role of storage and transmission for renewable energy integration. Energy for Sustainable Development, 88, 06 2025.

Global Wind Energy Council, Rebecca Williams, Feng Zhao, Nina Melkonyan, Mark Hutchinson, and Janice Cheong. Global offshore wind report 2025, June 2025.