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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 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]

The effect of converter impedance is mostly ignored when performing harmonic analysis, as it is complicated to calculate, and a common assumption is that it has minimal effect. This paper compares the use of simplified techniques against a rigorous calculation of the converter impedance and demonstrates their effect on the frequency response of the system. [ABSTRACT FROM PUBLISHER]

Marginal pricing of harmonic injections can be shown to encourage each member of the network to independently act in such a way that the harmonic profile of the system is optimized. A problem encountered with marginal pricing is that loads can be charged complex amounts for their injections. This paper demonstrates that the real part of the amount charged for any injection reflects the "in-phase" component of that current, which will either increase or decrease the prevailing harmonic voltages. The imaginary part charged to a load reflects the quadrature component of their injections, which has no effect on the voltage magnitudes, at the margin. Each load need only be liable for the real amount they are charged, which has a direct correspondence with the total payments due. [ABSTRACT FROM PUBLISHER]