Reinjection Concept Research Articles

Firing thyristors with negative firing angle using multilevel current reinjection concept: an experimental evaluation

Thyristor based multilevel current reinjection (MLCR) current source converter (CSC) provides self-commutation capability to thyristors. It also has high quality line current waveform by accurately shaping the DC bus current using an auxiliary reinjection bridge. However the theoretical and PSCAD/ETDC simulation analysis do not take into account the inevitable stray capacitances and inductances which may influence the thyristor turn-on/off and the simulation switching model may not represent the switching characteristics of the main bridge thyristors fully or accurately. Questions have been raised about the ability to achieve self-commutation with thyristors and the possibility of operating thyristors with negative firing angles. Therefore, it is necessary to experimentally verify whether neglecting the real-world artefacts actually impedes the performance of thyristor based MLCR CSC. The experimental results presented in this paper prove that the auxiliary reinjection circuit can force the thyristor to commutate independently from their respective line-to-line voltages and thyristor converter can operate with a negative firing angle.

DC Ripple Reinjection: A Review

This paper presents a comprehensive review of power quality improvements made by applying the concept of DC ripple reinjection in current source series connected AC-DC rectifier for HVDC transmission. Recent advances in applying the reinjection concept, their suitability and selection is discussed. The main aim is to present a state of the art on the DC ripple reinjection technique over the years.

Derivation of a Four-Quadrant Control System for MLCR-HVDC Conversion

Although the multilevel current reinjection concept has been presented as a possible self-commutating alternative to line-commutated conversion for large power HVDC transmission, in its present form, the lack of independent reactive power control at the two converter terminals constitutes a severe limitation to its eventual acceptability. For very large power ratings, the use of double-group converter terminals has been shown theoretically to overcome the reactive power interdependence; however, the high nonlinearities involved make it difficult to design a practical control system, which is the main purpose of this paper. Comprehensive PSCAD/EMTDC simulation is used to verify that the dynamic and steady-state response of the proposed control system design are perfectly satisfactory.

Reinjection concept: a new option for large power and high-quality AC–DC conversion

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.

Application of the multi-level current reinjection concept to HVDC transmission

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.

Application of the DC-Ripple Reinjection Concept to Forced-Commutated Conversion

A dc-ripple reinjection concept, described in the literature with reference to the line-commutated current source converter, is applied in this paper to the self-commutated current source converter. This is achieved by means of a reinjection converter fed, via a single-phase transformer, from the triple frequency ripple signal. It is shown that the three-phase bridge can be made to operate effectively at any multiple of the six-pulse number and, thus, presents an effective alternative to the use of ac and dc side filters.

Pulse Multiplication in the Self-Commutating Parallel Converter by Means of Multi-Level DC Voltage Reinjection

A multi-level dc voltage reinjection concept is described that multiplies the pulse number of the twelve-pulse dual parallel converter. The ideal reinjection waveform for complete elimination of the harmonic content is first derived, and a practical approximation is proposed which converts the standard dual converter into a sixty-pulse scheme, thus meeting the strictest harmonic standards without the assistance of filters or Pulse Width Modulation.

Multi-level voltage reinjection-a new concept in high voltage source conversion

A voltage source converter is proposed, in which the multi-step output voltage waveform is achieved by the reinjection of different DC voltage levels via the common neutral point of the converter bridges. The number of clamping switches are substantially reduced, permitting the use of higher level numbers to achieve very low distortion without the assistance of PWM. The reinjection concept causes the voltage across the main bridges to vary in step waveforms and the commutations in the main valves to occur at zero voltage, with considerably reduced dynamic voltage stress and switching losses.