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A new concept referred to as reinjection AC/DC conversion is described, applicable to both self-commutating voltage source and current source conversions. It combines all the benefits of the multi-level, soft switching and ripple reinjection concepts. The aim is to achieve high-quality waveforms, simplify the structural configuration and the interface with the grid, improve the conversion efficiency, limit the dv/dt and provide flexible active and reactive power controllability. [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]

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]

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]

Previous work conducted in the unified harmonic domain has been primarily focused on HVDC systems. The paper outlines the extension of this technique to a hard switched FACTS device. A unified harmonic domain model is developed for a STATCOM and solved using a Newton solution based on DC side current mismatches alone. This generic formulation maintains modularity, allowing the interaction between multiple STATCOMs to be studied. The model has been verified against a time domain solution using PSCAD/EMTDC. The proposed technique provides practically identical results, without the time domain's inherent problems with respect to steady-state 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]

Electromagnetic transient simulation can be used to model complex non-linearities that are very difficult to represent adequately in the frequency domain. After reaching the steady state the voltage and current waveforms, represented by sets of discrete values at equally spaced intervals (corresponding with the integration steps), are subjected to fast Fourier transform processing to derive the harmonic spectra. However, the accuracy of the EMTP approach is limited by the restricted frequency dependence representation of the AC system components. It is shown that this problem is greatly reduced with the use of frequency-dependent network equivalents for the linear part of the system. [ABSTRACT FROM AUTHOR]

Presents the formulation for developing a 1- and 2-port frequency-dependent equivalent of AC system using z-domain rational function fitting of the frequency response. Key motivation for investigating z-domain fitting; Indication of the robustness and accuracy of 1- and 2-port frequency-dependent network equivalent (FDNE) for electromagnetic transient simulation; Discussion on issues of developing a 1- and 2-port frequency-dependent equivalent of the AC system.