Interconnection of direct-drive wind turbines using a distributed HVDC converter station

This paper presents the concept of a ¿distributed HVDC converter station¿ for offshore wind farms. The proposed converter topology allows series interconnection of wind turbines with need of neither transformer nor offshore platform at the sending end. Each wind turbine is equipped with a 5MW permanent-magnet synchronous generator and an ac-dc-dc converter. The converter topology is a diode rectifier (ac-dc) cascaded with a single-switch step-down converter (dc-dc). The dc-dc stage allows the current to flow at all times in the dc link while regulating generator torque. The system is modeled in the PSCAD/EMTDC software package and a 150MW wind farm is simulated. Simulation demonstrates operation of the proposed configuration where each turbine is able to independently perform peak power tracking.