Design of a Tapped delta autotransformer based 20-pulse ac-dc converter is presented in this paper. The 20-pulse topology is obtained via two paralleled ten-pulse ac-dc converters each of them consisting of a five-phase (five-leg) diode bridge rectifier. For independent operation of paralleled diode-bridge rectifiers, a zero sequence blocking transformer (ZSBT) is designed and implemented. Connection of a tapped inter-phase transformer (IPT) at the output of ZSBT results in doubling the number of output voltage pulses to 40. The proposed structure has been implemented and simulated using Matlab/Simulink software under different load conditions. Simulation results confirmed the significant improvement of the power quality indices (consistent with the IEEE-519 standard requirements) at the point of common coupling. Results show that input current total harmonic distortion (THD) is less than 3% for the proposed topology at variable loads. Furthermore, near unity power factor is obtained for a wide range of DTCIMD operation.