Analysis of Double-Star Modular Multilevel Topologies Applied in HVDC System for Grid Connection of Offshore Wind Power Plants

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 100 MW. 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.