Journal of Control, Automation and Electrical Systems https://doi.org/10.1007/s40313-019-00542-2 Analysis of Double-Star Modular Multilevel Topologies Applied in HVDC System for Grid Connection of Offshore Wind Power Plants William Caires Silva Amorim 1 · Dayane do Carmo Mendonça 1 · Renata Oliveira de Sousa 1 · Allan Fagner Cupertino 1,2 · Heverton Augusto Pereira 3 Received: 3 June 2019 / Revised: 11 September 2019 / Accepted: 19 October 2019 © Brazilian Society for Automatics–SBA 2019 Abstract Reducing costs related to passive elements and ensuring ability to handle short-circuit faults are essential for a reliable and cost-effective operation of modular multilevel converters (MMCs) in high-voltage direct current (HVDC) systems. HVDC systems have emerged in offshore wind power plants (OWPP), as an attractive solution to connect OWPP to the main ac system. To address these challenges, this paper carries out a benchmarking of double-star (DS) MMC topologies applied to OWPP. In this sense, comparisons among DS topologies of the DSCC (double-star chopper cell), DSBC (double-star bridge cell) and DSHyb (double-star hybrid) types are proposed. Quantitative analyses are performed, considering an OWPP of 100MW. In the results, the topologies are compared for steady-state operation and active power dynamics. In addition, power losses and junction temperature through a one-year OWPP mission profile are analyzed. Due to dc fault tolerance and capacity to synthesize two times the converter output voltage in comparison with the DSCC, DSBC and DSHyb are best suited in HVDC systems. However, DSHyb stands out in terms of converter efficiency and capacitor energy storage. Thus, DSHyb proves to be a promising topology to connect OWPP to the ac system. Keywords Double-star topologies · Modular multilevel converter · High-voltage direct current · Offshore wind power plant. 1 Introduction Renewable energy sources have been massively applied in high-voltage direct current (HVDC) systems in recent B Heverton Augusto Pereira heverton.pereira@ufv.br William Caires Silva Amorim william.caires@ufv.br Dayane do Carmo Mendonça dayane.mendonca@ufv.br Renata Oliveira de Sousa renata.sousa@ufv.br Allan Fagner Cupertino afcupertino@ieee.org 1 Graduate Program in Electrical Engineering, Federal Center for Technological Education of Minas Gerais, Belo Horizonte, MG 30421-169, Brazil 2 Department of Materials Engineering, Federal Center for Technological Education of Minas Gerais, Belo Horizonte, MG 30421-169, Brazil 3 Department of Electrical Engineering, Universidade Federal de Viçosa, Viçosa, MG 36570-900, Brazil decades, mainly due to the long distance in transmission lines between generation systems and customers (Jung et al. 2017). In this regard, wind power plants, especially the off- shore type, allow greater energy production, compared to the onshore installation (Jung et al. 2017; Batista et al. 2017). The offshore installation expansion can be explained by its superior wind speed profiles compared with the onshore installation, besides the mitigation of noise, visual aspects, tower shading, among other aspects (Apostolaki-Iosifidou et al. 2019). Moreover, the offshore wind power plant (OWPP) in HVDC transmission system has been featured in facilities which are not less than 70 km away from the coast, compared with high-voltage alternating current (HVAC) (Batista et al. 2017). Regarding government policies, some countries have reduced the concessions for onshore installa- tion. For OWPP, voltage source converters (VSC) emerged as a topology with superior qualities compared with line com- mutated converters (LCCs) (Ghat et al. 2017). However, LCCs have been consolidated among the best converters for HVDC systems, due to their high applicability in practi- cal projects, with good operation of transmission capacities 123