TAPPED DELTA AUTOTRANSFORMER-BASED 40-PULSE AC-DC CONVERTER WITH REDUCED KILOVOLT-AMPERE (KVA) RATING FOR POWER QUALITY IMPROVEMENT

ABSTRACT-Design of a Tapped delta autotransformer based 20-pulse ac-dc converter with reduced kilovolt-ampere (kVA) rating 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 topology is basically constructed from a 20-pulse converter. The use of pulse doubling technique with a low rating (2% of the load power) results in increased number of pulses to 40. The circuit has been designed for retrofit applications, a tapped delta-connected autotransformer platform is also included to the converter. 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.

AC–DC converter, Tapped delta autotransformer, power quality, 40-pulse rectifier, Pulse doubling, direct torque controlled induction motor drive (DTCIMD).