The effect of high power DC-DC converter in offshore multi-terminal medium and high voltage DC networks

There is increasing interest in interconnecting individual wind turbines in offshore wind farms using DC networks rather than AC networks. As the output from each turbine/generator is normally low (less than 6 kV), DC-DC converters may be required to step-up the voltage to an intermediate level to interconnect the turbine outputs, and another DC-DC converter to step-up this intermediate voltage to a high level for transmission to the shore. As the output from the turbines varies with wind speed, the low to intermediate voltage converter are in particular needed to be able to control its output in order to maintain a constant DC level. Such converters will introduce harmonics into the DC network, potentially resulting in substantial losses in the cables.