Modular isolated high frequency medium voltage (MV) step-up resonant DC/DC converters with high-gain rectifier for wind energy systems

Conventional offshore wind farms with medium voltage (MV) AC grid require low frequency step-up transformer to boost the output voltage of the wind turbine. In order to eliminate the bulky MV step-up transformers in MVAC grid, the use of a MV step-up DC/DC converter in MVDC grid is an attractive alternative. In this paper, two modular MV step-up DC/DC converter topologies that combine multiple modules of step-up resonant circuits and high frequency high gain rectifiers are proposed for MVDC grid in wind energy system. Due to the combination of multiple step-up resonant circuits and the high gain rectifiers, the proposed converters are able to achieve high voltage gain without using large turns ratio high frequency step-up transformers. In addition, ZVS turn-on ZCS turn-off are achieved on the inverter side switches to minimize the switching losses. The switching frequency is varied to regulate the output medium voltage for different wind speed conditions. The description and the operating principles of the proposed converter are provided in this paper. Results on a 5MW, 3.3kVac/40kV wind turbine system are presented to highlight the merits of this work.