Topology Design for Collector Systems of Offshore Wind Farms With Pure DC Power Systems

This paper presents an analytical design method for the dc collector systems of offshore wind farms and proposes an improved topology to overcome the limitations of the conventional series-parallel (SP) topology. During a severe failure in the SP topology, bypassing the faulty units imposes overvoltage on fault-free units and leads to the disconnection of the series branch from the collector system. By providing auxiliary connection paths, the suggested topology reduces the overvoltage of the units and hence maintains fault-free units operational following a severe failure. Hence, the efficiency of a wind farm increases considerably upon any failure occurrence. To show the merits of the suggested topology, the captured power during a failure has been calculated and fairly compared with that of the conventional SP topology, considering the excess cost of the suggested topology due to additional connection paths. To investigate the performances of both topologies and their feasibility, a collector system including 12 wind turbine generators has been simulated in time domain software environment. Then, various failure scenarios have been investigated to evaluate the transient behavior of the dc collector system following slight and severe failures. The study results reveal the feasibility of the proposed topology as a promising structure for future dc collector systems.