Hybrid, multi-megawatt HVDC transformer for future offshore wind farms

As the offshore wind industry moves further offshore HVDC transmission is becoming increasingly popular. HVDC transformer substations are not optimised for offshore industry however, increasing costs and reducing redundancy. A suggested modular hybrid HVDC transformer located within each wind turbine nacelle could mitigate these problems however, careful design is required to minimise losses. For example converter topology will influence the semi-conductor and magnetic transformer losses. In this paper several hybrid transformer configurations comprising combinations of the H-Bridge and Modular Multilevel Converter topologies are modelled in the Matlab/Simulink environment. The configurations are evaluated for use in the suggested medium frequency HVDC transformer based on their contribution to total losses, their stability and range of real and reactive power control.