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A three-phase converter configuration, with each phase consisting of a series chain of H-bridges has become a popular multilevel solution for STATCOM application. Such a configuration, however, is not suitable for HVDC transmission. A new concept, where the series chain of H-bridge cells is used to derive a multilevel voltage reinjection waveform, is described in a companion paper. Its application to HVDC transmission is discussed in this paper and extensive use is made of EMTDC simulation to verify its steady-state and dynamic behavior. [ABSTRACT FROM AUTHOR]

In self-commutating multi-level voltage source conversion (VSC) transmission, the reactive power contributions of the two converter terminals are interdependent. To overcome this problem, a new control scheme is proposed, applicable to high voltage direct current (HVDC) interconnections of large power ratings with more than one 12-pulse group per converter. The basis of the proposed strategy is the use of a controllable phase shift between the firings of the individual converter groups. The theory is verified by extensive EMTDC simulation. [ABSTRACT FROM AUTHOR]

A new self-commutated AC-DC converter is proposed based on the reinjection of multilevel DC pulses via the mid-point of the series double-bridge converter using a GTO-switched multitapped single-phase transformer. The ideal reinjection waveform for complete elimination of the harmonic content of the AC-side current is derived and a practical approximation proposed to increase the pulse number of double-bridge converters to any multiple of 12. A 60-pulse configuration is analysed in detail to show effectiveness on both the AC and DC sides of the converter. [ABSTRACT FROM AUTHOR]