High voltage high power DC/DC modular multilevel converter for offshore windfarm DC collection point

摘要

This paper presents a new high voltage high power DC/DC converter suitable for off-shore windfarm application. The proposed converter functions as a DC collection point and boosts the wind generators' voltages to facilitate the employment of high voltage direct current (HVDC) transmission lines. The proposed converter utilizes the modular multilevel converter (MMC) structure and combined converter linked by the medium frequency transformer, which leads to lower voltage and current stresses of diode bridge rectifier compared to the conventional DC/DC converters while using relatively smaller transformer. This topology features modularity, which significantly improves system's reliability and implementation. A new control method is also derived for the proposed converter and the effectiveness of the system is demonstrated with various operating conditions.