The ever increasing progress of high-voltage high-power fully controlled semiconductor technology continues to have a significant impact on the development of advanced power electronic apparatus used to support optimized operations and efficient management of electrical grids, which, in many cases, are fully or partially deregulated networks. Developments advance both the HVDC power transmission and the flexible ac transmission system technologies. In this paper, an overview of the recent advances in the area of voltage-source converter (VSC) HVdc technology is provided. Selected key multilevel converter topologies are presented. Control and modeling methods are discussed. A list of VSC-based HVdc installations worldwide is included. It is confirmed that the continuous development of power electronics presents cost-effective opportunities for the utilities to exploit, and HVdc remains a key technology. In particular, VSC-HVdc can address not only conventional network issues such as bulk power transmission, asynchronous network interconnections, back-to-back ac system linking, and voltage/stability support to mention a few, but also niche markets such as the integration of large-scale renewable energy sources with the grid and most recently large onshore/offshore wind farms.

VSC-Based HVDC Power Transmission Systems: An Overview

Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

In this paper, the principle of modularity is used to derive the different multilevel voltage and current source converter topologies. The paper is primarily focused on high-power applications and specifically on high-voltage dc systems. The derived converter cells are treated as building blocks and are contributing to the modularity of the system. By combining the different building blocks, i.e., the converter cells, a variety of voltage and current source modular multilevel converter topologies are derived and thoroughly discussed. Furthermore, by applying the modularity principle at the system level, various types of high-power converters are introduced. The modularity of the multilevel converters is studied in depth, and the challenges as well as the opportunities for high-power applications are illustrated.

Modular Multilevel Converters for HVDC Applications: Review on Converter Cells and Functionalities

New regulations impose more stringent limits on current harmonics injected by power converters that are achieved with pulsewidth-modulated (PWM) rectifiers. In addition, several applications demand the capability of power regeneration to the power supply. This work presents the state of the art in the field of regenerative rectifiers with reduced input harmonics and improved power factor. Regenerative rectifiers are able to deliver energy back from the dc side to the ac power supply. Topologies for single- and three-phase power supplies are considered with their corresponding control strategies. Special attention is given to the application of voltage- and current-source PWM rectifiers in different processes with a power range from a few kilowatts up to several megawatts. This paper shows that PWM regenerative rectifiers are a highly developed and mature technology with a wide industrial acceptance.

http://www.lcda.cl/descargas/rodriguez_dixon_pont_espinoza_lezana05.pdf

PWM regenerative rectifiers: state of the art

The changing nature of residential network loads means that Power Quality is becoming a significant issue in New Zealand and internationally. Many residential appliances have electronic power converters that characteristically draw a non-sinusoidal current waveform. This results in increased harmonic voltage levels in the distribution network. The total impact depends on the number of appliances, their power ratings, and their harmonic diversity. A measurement survey has been performed of different categories of modern appliances to determine their Power Quality characteristics. In addition, computer modelling of the appliances on a typical distribution feeder shows their relative harmonic voltage impact.

http://ieeexplore.ieee.org/iel5/5706732/5710678/05710787.pdf

The effect of new residential appliances on Power Quality

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.

Multilevel current reinjection self-commutated HVDC converter

A widened harmonic power flow algorithm is described capable of determining the interaction between the fundamental, harmonic, and interharmonic frequency components. The algorithm is multiphase and can include any number of nonlinearities. The New Zealand power system is used to illustrate the ability of the algorithm to determine the harmonic interaction between an HVDC link and an aluminum smelter.

A multifrequency power flow of general applicability

There is a growing use of High Voltage Direct Current (HVDC) globally due to the many advantages of Direct Current (DC) transmission systems over Alternating Current (AC) transmission, including enabling transmission over long distances, higher transmission capacity and efficiency. Moreover, HVDC systems can be a great enabler in the transition to a low carbon electrical power system which is an important objective in today’s society. The objectives of the paper are to give a comprehensive overview of HVDC technology, its development, and present status, and to discuss its salient features, limitations and applications.

An Overview of HVDC Technology

The power system is undergoing dramatic change as deregulation occurs. Since customers have more choices power quality is becoming a bigger issue and now entering electricity supply contracts. In such cases power quality indices are important in characterizing the quality of the voltage waveform. This allows power quality to be specified in contracts and verified. Moreover this allows a quantitative comparison of the power quality between various systems, as well as the effect of various proposals on the power quality of a system. This paper introduces RMS error and normalised RMS error as global power quality indices and shows how they can be applied.

Neville R. Watson

Papers

The effect of new residential appliances on Power Quality

Multilevel current reinjection self-commutated HVDC converter

A multifrequency power flow of general applicability

An Overview of HVDC Technology

A global power quality index for aperiodic waveforms