This paper discusses the impact of using 3-phase and multipules converter circuit commonly found in unity power factor at

input AC mains and regulates output voltage.3-phase thyristor rectifiers have been used in industries for obtaining a variable DC

voltage, but they have a problem of including large lower-order harmonics in the input currents. For high-power applications, a 12-

pulse, 18-pulse and 24-pulse configuration is useful for reducing the harmonics, but it still includes the (np±1) th (n: integer, p: pulse)

harmonics. In this paper present the rectifiers are using the MATLAB/SIMULINK simulation model and several common conditions

will be simulated to compare their harmonic levels.