A front-to-front (FTF) system consisting of two modular multilevel cascade converters based on double-star chopper-cells

This paper presents a medium-voltage high-power dc-dc converter using two modular multilevel cascade converters based on double-star chopper-cells (MMCC-DSCC) for power collection. The system configuration is applicable to multi-terminal dc power networks such as off-shore wind farms. The system can be extended to use several MMCC-DSCCs at the power-collecting side (lower dc voltage side) which connected together at the ac side of the converters via a galvanic isolation. Furthermore, the system can handle dc faults inherently and existing ac circuit breakers can be used instead of dc circuit breakers for fault protection. The circuit configuration and the control method are described along with simulated results that verify the proposed front-to-front system.