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A new self-commutated current source converter is proposed, based on the reinjection of multi-level dc current pulses via a GTO-switched multi-tapped interphase reactor. The ideal reinjection waveform for complete elimination of the harmonic content of the ac system side current is derived and a practical approximation proposed to increase the pulse number of the double-bridge converter to any multiple of twelve. A 48-pulse configuration is analyzed in detail to show the new concept effectiveness on both the ac and dc sides of the converter. Index Terms--AC-DC conversion, current source conversion, harmonics, multilevel.

The proposed converter is based on the reinjection of a series of dc voltage pulses, at a frequency multiple of the fundamental, that shape the output voltage waveforms into a multilevel scheme. The reinjection ratio and frequency are chosen to convert the standard 12-pulse into 36-pulse configuration without the assistance of filters or PWM. Thus, the switching losses are greatly reduced. The harmonic current injection can be kept within present standards by an appropriate choice of the interface transformer leakage reactance. Index Terms--Voltage source converter, multi-level voltage reinjection, fundamental switching.

The high-power self-commutated voltage-source converter (VSC) and current-source converter (CSC) are the key control devices in high-voltage direct current, flexible ac transmission systems, and distribution flexible ac transmission systems. To achieve the expected control objectives, suitable control strategies must be implemented based on the available devices, system models, and control techniques. The self-commutated ac/dc converters control the electrical power by generating controllable ac fundamental and dc average outputs. These controllable outputs are controlled by the conducting state combinations of the converter switching devices, driven by their gate signals. The gate signals are specified by fundamental parameters of frequency, amplitude, and phase angle. The converter system model for describing the relation between the system-state variables and the gate signal parameters is essential for the converter system control strategies. The companion paper (Part I) derives the state variable equations for the transmission systems using voltage-source-type converters. Part II is for the transmission systems using current-source-type converters. The self-commutated converter systems provide control flexibility of active and reactive powers, but their nonlinearity makes their control difficult. The linearized state equations using feedback linearization are presented to enable the controller design by using linear control theory. [ABSTRACT FROM PUBLISHER]