A review on MVdc collection systems for high-power offshore wind farms

Recently, offshore renewable technologies have shown a rapid growth with the advancement in technology together with reduction of capital investment per unit size. This movement is further catalyzed by various government policy decisions and new set targets on renewable energy (RE) production. Due to higher wind speed, limited land availability and flexibility of transporting very large structures (with the increased size of a single wind turbine) offshore wind power plants provide commendable benefits over onshore wind plants. At present, only medium voltage ac is used in the offshore wind collection systems. However, the use of medium voltage direct current (MVdc) at the collection level is becoming more attractive due to advantages like lower systems losses, zero reactive power compensation and flexibility of power flow control compared to traditional ac collection systems. This paper intends to review opportunities and key challenges associated with the emerging MVdc technology for offshore wind collection systems. Attention is given to the DC wind turbine concept and selecting a suitable MVdc collection system topology with appropriate control modes