A Multilevel Step-Up DC-DC Converter for Interfacing Offshore Wind Turbines with DC grids

This paper presents a promising multilevel step-up DC-DC converter architecture for interfacing offshore wind turbines to HVDC grid. The converter employs multi-primary, single common secondary novel adder transformer configuration. The multiple primaries are individually fed with high frequency resonant inverters and the secondary ’added’ or step-up voltage is subsequently rectified by a voltage doubler rectifier. Half-bridge modular multilevel converter modules (MMC) are used to implement the voltage doubler, thereby enabling the converter to be suitable for HVDC applications. The proposed converter architecture is designed to generate 160kV at 1 - 10MW from a rectified output of a variable speed wind turbine generator. Soft-switching transition is maintained for all switches for all operating conditions. A scaled experimental prototype with a power range 0.15 - 0.4kW, at input voltage range of 37 - 80V with peak efficiency of 97.66% is built as a proof of concept.