Single-stage three-phase AC/DC step-up medium voltage resonant converter for offshore wind power systems

Conventional offshore wind farms with AC power transmission require multiple line frequency step-up transformers to boost the output voltage of the wind turbine generator for High Voltage AC (HVAC) transmission. In order to eliminate the bulky AC transformers, DC power transmission has been suggested in literatures for wind farms by utilizing medium voltage step-up DC/DC converter to boost the output voltage of the wind turbine to the medium voltage DC grid. To improve the overall system efficiency and reduce the number of conversion stages in DC transmission, a new single-stage AC/DC step-up resonant converter with softswitching is proposed in this paper. The proposed converter combines the three-phase boost rectifier and a high voltage gain CL resonant converter into a single-stage converter. Two strings of switch pairs are connected in series in the proposed converter so that the voltage stress across each power transistor is only half of the DC-link voltage. Results are given on a 3MW, 3.3kV_rms/30kV wind turbine system to highlight the merits of the proposed circuit.