Analysis and Implementation of Multi Pulse Converters for HVDC System

It is well known that undesirable harmonic line currents may be generated during a transformer-rectifier combination. The rectification of AC power to DC power itself may in general produce undesirable current harmonics. These non-linear loads cause severe current harmonics that may not be tolerated by either a shutdown of the device or unacceptable powering of the devices. The great majority of power electronic equipment operates from an ac source but with an intermediate dc link. Thus, a significant opportunity exists to facilitate power electronics applications by using ac to dc rectifiers that produce low harmonic current in the ac source. Multi-pulse converters in general and non-isolated multi-pulse converters in particular can be applied to achieve clean power which is of major interest in higher power ratings. In general, by increasing the number of pulses in multi-pulse converters THD (total harmonic distortion) can be reduced and other associated performance parameters can be enhanced. The present work is an endeavour towards analysing the different multi-pulse AC to DC converters in solving the harmonic problem in a three-phase converter system. The effect of increasing the number of pulses on the performance of AC to DC converters is analyzed. For performance comparison the major factor considered is the total harmonic distortion (THD). Keywords— Power Quality, Harmonics, Total Harmonics Distortion