Review of wind farm power collection schemes

The main development trend of wind power generation systems is large offshore wind farms (OWFs) with grid connection. However offshore wind farms have grown rapidly due to much better wind conditions. Hence, several large scale offshore wind farms are planned to be built and installed at distances greater than 100 km from the coast. Traditionally, an AC collector scheme collects energy from the wind farm and step up the voltages by power transformers and transmit power via AC submarine cables to the onshore substation. However, this is suitable for shorter distances about 50 km. When the distances are greater the AC transmission of bulk power from the wind farm to the onshore grid via undersea cables is not viable due the reactive power issues. Therefore HVDC transmission is now being considered for the grid connection of wind farms. However as wind farms constitute weak systems Line commutated converter (LCC) based HVDC is not viable and newer Modular Multilevel Converter (MMC) based Voltage Source Converters(VSC) are needed for AC-DC conversion. Opting for dc systems for both power collection and transmission pose a number of technical challenges in terms of developing HVDC breakers and DC -DC converters.