Ac vs. dc distribution for off-shore power delivery

This paper compares AC and DC transmission schemes for power delivery between land-based and off-shore installations. The comparison is focused on the loss, as well as on the technologies needed for each of these systems. The study shows that both AC and DC schemes can provide feasible solutions for off-shore applications. Specifically, it is shown through analysis and simulation, that DC distribution always results in lower loss for a given voltage level and a given transmission cable. In fact, depending on the voltage and cable parameters, the DC system loss could be as low as 15 to 50% of that of the corresponding AC system. The latter loss nonetheless could be reduced by the use of proper compensation at the expense of an increased complexity and cost. The study also shows that higher voltages are desirable for high power and long distance power distribution. This is advantageous for the AC scheme, which can readily use transformers at both sending and receiving ends, but represents a disadvantage for the DC case given that high-voltage DC-DC converters are a less mature technology. To this end, a modular converter topology is proposed that could be used for high voltage DC power delivery achieving a lower cost and size, better controllability, and higher reliability.