Power Quality Analysis Of Six- And Twelve-Pulse Rectifiers As Series Cascaded Topologies Of The Three-Pulse Rectifier

Multipulse rectifier topologies comprise power diodes and are essentially three-phase unidirectional ac-dc converters. The pulse number (n) of a rectifier, defined as the number of dc voltage notches corresponding to a time period of the ac source is an important index that influences several power quality parameters associated with rectification. The parameters used to assess the efficacy of ac to dc conversion encompass characteristic harmonics including the least order harmonic (LOH) and the total harmonic distortion (THD) of the input ac line currents, number of commutations undergone by the rectifier in a cycle of the ac source voltage, power factor, distortion factor, fundamental power factor (displacement factor), transformer utilization factor (TUF) on the ac side; and voltage regulation, ripple frequency, voltage harmonics, crest factor (CF), form factor (FF), ripple factor (RF), rectification factor on the dc side. The six- and twelve-pulse rectifiers are deployed extensively in many applications. While the six-pulse bridge topology is ubiquitous in ac and dc drives, welding, electroplating, electrolysis, electric vehicles etc. The twelve-pulse topology that can be obtained as a series cascade of two six-pulse bridge topologies is used in high voltage dc transmission (HVDC). In this paper, the three-pulse rectifier is analyzed from the power quality perspective and the performance parameters of the six-pulse bridge topology are derived from the series cascade of two three-pulse rectifiers. The analysis is extended to the twelve-pulse topology as well. The analyses is validated by experimental results from the three-, six-, and twelve-pulse topologies.