Multi-level Current Reinjection Current Source Converter

A new concept of Multi-Level Current Reinjection (MLCR) AC/DC conversion is described in this thesis. It is a combination of the multi-level conversion, soft switching and reinjection conversion. It is an attempt to reduce the harmonic content, to balance the voltages of the direct series connected power switches and to improve the efficiency and reliability of high power AC/DC converters.To achieve the ideal AC/DC conversion, the ideal reinjection waveforms are first derived for perfect harmonic cancellation and then fully symmetrical approximations are made to reduce the complexity for practical implementations. This is followed by a description and comparison of the reinjection circuits required for generating of the multi-level symmetrical reinjection waveforms.Two types of the MLCR Current Source Converters (series and parallel) are proposed. In the series configuration a reinjection circuit and reinjection transformers are added into the standard 12-pulse converter; the multi-tapped reactor and a set of forced-commutated switches connected with the reactor are used to divide the DC current to the two main bridges periodically in the parallel configuration. For each configuration the firing sequences, waveform analysis, conversion performances and control strategies are presented.The high quality waveforms of the proposed converters are verified by EMTDC simulations. As an application example, a 48-pulse equivalent MLCR-CSC use as STATCOM is simulated. The simulation results show that the converter produces high quality output waveforms,provides flexible controllability of inductive and capacitive powers and quick dynamic response, operates properly under symmetrical and asymmetrical even abnormal source conditions.