Isolated Cascaded DAB DC-DC Converter to Boost Medium DC Voltage to HVDC

Abstract

The offshore wind farms typically use ac system to collect power from each generator, with the voltage increased by means of high, heavy step-up transformers. DC collection grids have also recently been taken into consideration as a solution to simplify and minimize offshore wind farm platforms. DC collection grids offer an additional method to reduce the complexity of offshore wind farms. However, increasing the DC voltage for HVDC transmission requires the  development  of  high-power  and  high-voltage  converters,  which  presents  a  technical  challenge.  This  research makes  use  of  an  isolated  cascaded  dual  active  bridge  (DAB)  DC-DC  converter  to  boost  medium  DC  voltage  to HVDC. Isolated  Cascaded  DAB  DC-DC  Converters  are  connected  in  series  on  the  output  side  and  in parallel  on  the input side to obtain a high transformation ratio and high power. The bidirectional DAB DC-DC converters cab be designed with power densities in the variability of tens to hundreds of kilowatts, depending on the components used and the switching frequency at which the converters function most effectively. The input parallel output series (IPOS) topology, 225 kV HVDC can be generated from a 5 kV MVDC input by cascading DAB DC-DC up to 30 stages. This converter family is useful due to its scalability and flexibility since the power and voltage ratings can be increased while still using the same cells. MATLAB Simulink simulations are performed and verify the elementary operating characteristics of the system.