Six pulse rectifiers that are used in grid interfaces of variable speed drives draws currents that include harmonic components from grid. Increasing the rectifier pulse number of the rectifier is one of the useful methods that are used to keep the harmonic in the limits of international standards. In this study, a near unity power factor 30 pulse rectifier is designed for alternating current motors that operate under heavily varying load conditions. 12 degrees phase shifted five three-phase voltage sets that are needed for 30 pulse rectification are generated by proposed star-differential autotransformer. Proposed autotransformer's power is only 20.9% of output power. So transformer size and system total cost is reduced. The designed autotransformer is modeled and simulated with MATLAB/Simulink. It is seen from simulation results that, the line current harmonics of the 30 pulse rectifier are in the limits of international standards even under the light load condition, and the nearly unity power factor is achieved.