Offshore wind farm based on variable frequency mini-grids with multiterminal DC interconnection

This paper studies a large offshore wind farm interconnected to the grid using a multiterminal HVDC link. The 200 W wind farm consists of 100 individual 2 MW turbines connected using 25 CSI (current source inverters) to a common DC link. Since The CSI converters are in series connection, no generator transformers are needed to elevate the voltage. The transmission system converters enable regulation of the generator speed. The converters are not needed with individual generators, implying that simple permanent magnet generators can be used. The paper presents PSCAD simulation for various changes in wind speeds. The results confirm the ability to operate at optimum coefficient of performance and that there are no synchronization problems even for severe wind speed changes. The proposed concept may enable integration of large offshore wind farms at considerable distances, and using optimal number of converters.