Analysis of medium-voltage direct-current collector grids in offshore wind parks

The amount of grid-connected power electronic converters rises especially due tothe increasing power generation based on renewable energy sources. Due to thefact that photovoltaics and wind turbines operate internally with dc voltages, thelossy pulse-width modulated inverter and grid filter become obsolete when a dcgrid is used instead of an ac grid for energy collection. Furthermore, investmentcosts as well as maintenance and repair expenditures can potentially be reduced.This thesis investigates design approaches for dc collector grids in offshore windparks with and without internal voltage step-up converters. The required dc-dcconverters are discussed in detail but also the investment and operational costsof the electrical infrastructure. At the end, the investigated dc collector grid iscompared with an established ac collector grid approach. It can be concluded,that depending on the system design, dc collector grids are superior against acgrid approaches