Tapped Star Transformer-Based 72-Pulse AC-DC Converter for Power Quality Improvement

Design of a tapped star transformer based 36-pulse ac-dc converter is presented in this paper. The 36-pulse topology is obtained via two paralleled 18-pulse ac-dcconverters each of them consisting of a 9-phase (9-leg) diode bridge rectifier. A transformer is designed to supply therectifiers. The design procedure of magnetics is in a way suchthat makes it suitable for retrofit applications where a six-pulse diode bridge rectifier is being utilized. For independentoperation 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 72. The proposed structure has been implemented and simulated using Matlab/Simulink software under different load conditions. Simulation results confirmed the significantimprovement of the power quality indices (consistent with the IEEE-519 standard requirements) at the point of commoncoupling. 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.

Keywords:

AC–DC converter , tapped star transformer , power quality , 72-pulse rectifier , Pulse doubling , direct torque controlled induction motor drive (DTCIMD)