Abstract
A new self-commutated current source converter is proposed, based on the reinjection of multi-level dc current pulses via a GTO-switched multi-tapped interphase reactor. The ideal reinjection waveform for complete elimination of the harmonic content of the ac system side current is derived and a practical approximation proposed to increase the pulse number of the double-bridge converter to any multiple of twelve. A 48-pulse configuration is analyzed in detail to show the new concept effectiveness on both the ac and dc sides of the converter.
Highlights
A COMMON alternative to the use of filters to limit the harmonic content produced by current source ac/dc converters is increasing the pulse number, i.e., the number of dc-ripple pulses per cycle of the fundamental frequency
This is normally achieved by multi-bridge configurations with appropriately phase-shifted converter transformers, a solution that has not been found economical for high voltage application beyond the twelve-pulse configuration
A simpler multi-level concept was proposed a quarter of a century ago for the line-commutated ac/dc converter under the name of dc-ripple reinjection [6], that produces the same effect as converter transformer phase-shifts, i.e., it increases the number of pulses of the dc voltage and the number of steps of the ac current waveforms
Summary
A COMMON alternative to the use of filters to limit the harmonic content produced by current source ac/dc converters is increasing the pulse number, i.e., the number of dc-ripple pulses per cycle of the fundamental frequency. This is normally achieved by multi-bridge configurations with appropriately phase-shifted converter transformers, a solution that has not been found economical for high voltage application beyond the twelve-pulse configuration. When the ripple reinjection concept is applied to the parallel double bridge configuration, the interface reactor (acting as an autotransformer) is provided with multiple thyristor-controlled taps [7], which are switched sequentially at six times the fundamental frequency. In this paper the naturally commutated thyristor switches of the original current source conversion scheme [7] are replaced by fully controllable symmetrical devices (either GTOs or IGCTs) and the dc reinjection concept is revisited
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