Control of DAB Converters in Series-DC Wind Farm Based on 2DOF PI Controller

Utilizing medium voltage dc transmission in offshore wind farms can address various challenges that come with traditional ac transmission systems. In a series-connected dc wind farm architecture, the dc output power of each wind turbine is combined in series to attain a higher voltage level. This eliminates the need for bulky transformers and an offshore platform. The obtained medium voltage dc could be transmitted to the shore through relatively long subsea cables. Dual active bridge converters are being implemented in many applications that require high-power dc-dc converters. This paper proposes a new voltage control method for dual active bridge converters in a series-connected dc wind farm based on two-degrees-of-freedom 2DOF PI controllers. The controller is used to control the dc bus voltage for each wind turbine separately and is designed based on the reduced-order model of the converter. Simulation results verified the effectiveness of the proposed controller under different operating conditions.