DC Collection Systems for Large Scale Offshore Wind Farms

The power generated by individual offshore wind turbines requires a collection method before export to the onshore grid. At present, all grid-connected offshore wind farms use medium voltage AC as the collection method. This classical AC collection system requires a platform-supported transformer and centralized AC–DC converter which will present a significant share of the total loss and increases the capital investment. However, the use of medium voltage DC (MVdc) with Series or Series-Parallel topologies requires no centralized offshore collection platform and a high transmission voltage is obtained when summing up the individual turbine voltages. Nevertheless, reliability and capital investment are two of the major decision factors when selecting a suitable collection system configuration. This work mainly focusses on identifying a reliable-cost effective MVdc converter for offshore DC collection system. Further, it discusses possible system issues due to the deployment of power electronic rich DC collection systems.