LAUSR

A 30-pulse rectifier using passive voltage harmonic injection method at dc link is proposed in this article. The passive voltage harmonic injection circuit has a function to reduce the characteristic harmonics of the input voltage. Through injecting square wave voltage whose frequency is six times of the supply frequency into the dc link of the rectifier, some existing harmonic at the input voltage of the rectifier is reduced, so that the steps number of the rectifier increases from 18 to 30. The equivalent model of the rectifier bridges is established. The switching functions of the harmonic injection circuit and the rectifier bridges are analyzed, the operation modes of the rectifier are obtained, then the formation processes of the input voltage are analyzed, the quantitative relationship between the input voltage of the rectifier and the turn ratio of the injection transformer is obtained. The simulation and experimental results show that the total-harmonic distortion values of the input voltage and input current are reduced after using the harmonic injection circuit. In unbalanced conditions, the harmonic injection circuit still has good harmonic suppression performance.