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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]

The self-commutating multilevel current reinjection (MLCR) reduces the converter current waveform to zero during the valves commutations and, thus, removes the converter dependence on line commutation. This property provides the conventional thyristor converter with the same flexibility as the self-commutating multi-level schemes in terms of reactive power control and harmonic elimination. This paper describes the structure and control of a current source HVDC transmission scheme using MLCR converters. Extensive EMTDC simulation is carried out to demonstrate the improved controllability of the proposed HVDC configuration. [ABSTRACT FROM AUTHOR]