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Large-current, low-voltage applications such as aluminium smelters use diodesaturable reactors or thyristor-based rectification to control the DC current. Transformer on-load tap-changers are also used to minimise the steady-state reactive power requirements. This paper describes a new double-group, two-quadrant thyristor-based concept suitable for high current, where several thyristor and insulated gate bipolar transistor bridges are paralleled. By using a combination of leading and lagging firing angles, high power-factor is maintained and supplying bridges via phase shifting transformers enables continuous high-pulse operation. The theory is verified by EMTDC simulation. [ABSTRACT FROM AUTHOR]

A new multi-level VSC is proposed with highly reduced voltage and current harmonic distortion, without the need for filters or PWM. The multi-pulse waveform is achieved by means of two auxiliary reinjection bridges, which produce voltage pulses at six times the fundamental frequency. The proposed scheme simplifies the switching circuitry of present schemes for similar levels of waveform distortion and can operate in four quadrants without capacitor balancing problems. [ABSTRACT FROM AUTHOR]

A new STATCOM configuration is described in this paper that combines the advantages of the diode clamped, dc. voltage reinjection VSC and soft switching concepts. The new scheme uses asymmetrical switches instead of diodes in a common clamping switching circuit for the three-phases of the converter bridges. Detailed analysis is provided of the steady state output voltage and current waveforms. It is shown that this configuration provides very low distortion levels with greatly simplified auxiliary switching arrangements and reduced switching losses. [ABSTRACT FROM AUTHOR]