This thesis presents the introduction, analysis and experimental verification of the six-pulse SCR rectifier and multi-pulse SCR rectifiers. As a fundamental three-phase controllable ac-dc converter, the six-pulse SCR rectifier is widely used in industry. However, it generates high Total Harmonic Distortion (THD) in the line current. One of the solutions is to use multi-pulse rectifiers. Multi-pulse rectifiers could be classified into the 12-, 18-, and 24-pulse configurations. Application examples include high voltage direct current transmission systems, high power battery chargers and load commutated current source inverter powered motor drives. In this thesis, the six-, 12-, 18- and 24-pulse SCR rectifiers with inductive and capacitive loads are introduced. The line current THD and the input PF of various rectifiers are investigated. The principle of the harmonic elimination through phase-shifting transforms is analyzed by Fourer analysis and positive/negative sequence analysis. The experimental verification is accomplished on a prototype of the 12-pulse SCR recitifier.