A Simple Harmonic Reduction Method in 20-Pulse AC-DC Converter

This paper proposes a simple and passive harmonic reduction method at dc link of 20-pulse rectifier. The 20-pulse topology is obtained via two paralleled 10-pulse ac-dc converters, each of them consisting of a five-phase (five-leg) diode bridge rectifier. For independent operation of the 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 the ZSBT results in doubling the number of the output voltage pulses. The application of the pulse doubling technique with a low power rating (2% of the load power rating) results in a simpler and more economical con figuration of the whole system and increased number of pulses. The design is suitable for retro fit applications where a six-pulse diode bridge rectifier is being utilized. The proposed structure is simulated using Matlab/Simulink software under different loading conditions. The simulation results con firm the significant improvement of the power quality indices (IEEE-519 standard requirements) at the point of common coupling (PCC). Experimental results are obtained using the designed and constructed laboratory prototype of the proposed converter to validate the design procedure and the simulation results. The VA rating of the magnetic circuit is calculated to con firm the savings in space, volume, weight and cost of the proposed configuration.