Controlled/uncontrolled rectifiers draw harmonic reach currents from the grid. Harmonic components of the line current affect the grid and other equipment around the point of common coupling. Therefore, so the grid current harmonic distortion levels must be kept at desired level. Multi-pulse rectifiers are commonly used in high power rectifier systems to reduce grid current harmonics and improve power factor. In this study, design, simulation and application of a 18 pulse controlled rectifier for constant DC output under varying load conditions has been introduced. The proposed system consists of 0.218 kVA rated differential star connected phase shifting autotransformer to reduce the size and cost of the system. Experimental results of 6 and 12 pulse controlled rectifier are also given for comparison reasons. Simulation and experimental results show that the grid current harmonics are reduced and kept below the acceptable levels, and the power factor is also unproved by using 18 pulse controlled rectifier.