一种基于九桥臂MMC的混合多频率变流器OA

Aiming at the interconnections requirements of power frequency(PF),low frequency(LF)and direct current(DC)brought by the offshore wind power,a hybrid multi-frequency converter was designed based on the nine-bridge-arm modular multilevel converter(9A-MMC),in which the diode-clamp sub-module was selected for upper and lower bridge-arm,and the cross-connected-double sub-module was selected for intermediate bridge-arm.The converter had fewer components than the existed hybrid 9A-MMC with the ability of blocking DC fault,and its middle arms could output a negative voltage without controlling the current direction.An improved modulation method was designed for the intermediate bridge-arm module to effectively reduce harmonics.The simulation results show that the proposed hybrid 9A-MMC could simultaneously convert PF AC and LF AC into DC,with a low harmonic distortion rate and small DC-side voltage ripple,which is of certain significance for engineering.