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.

/pdf/a-review-of-single-phase-improved-power-quality-ac-dc-2pm6h4zjxq.pdf

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

Subject Definition and Objectives

The technical and economic advantages of HVDC transmission using self-commutated voltage source conversion, (VSC) otherwise known as HVDC Light, has seen a rapid uptake of this technology. This paper presents a method of incorporating self-commutated voltage source conversion into power-flow analysis by formulating the dc equations and Jacobian matrix to represent VSC. This new ac/dc power-flow algorithm is then demonstrated on a test system consisting of an HVDC link interconnecting two otherwise separate power systems.

http://ieeexplore.ieee.org/iel5/4494446/4509990/04510102.pdf

Incorporation of VSC transmission in power-flow simulation

A multi-level voltage reinjection concept, already shown to provide acceptable harmonic reduction with fewer switching components than the conventional multi-level schemes, is described in this paper with reference to its performance when operated as a STATCOM. EMTDC-PSCAD is used to illustrate the steady state and fast dynamic response to system changes, both under symmetrical and asymmetrical terminal voltage conditions

STATCOM Performance of A Multi-Level Voltage Reinjection Converter

High and increasing voltage Total Harmonic Distortion (THD) and 5th harmonic voltage levels have been measured in recent years on Orion NZ Ltd's rural 11 kV distribution network in Canterbury, New Zealand. On occasion, at Points of Common Coupling (PCC), the THD has exceeded the 5% limit and the 5th harmonic has exceeded the 4% limit. It has been suspected that these summer season high harmonic levels are due to the large existing and increasing density of farm irrigation deep well pump loads. It is likely that adverse effects on the network and neighbouring loads would become apparent if the increasing harmonic levels are left unchecked. A practical and theoretical investigation was conducted by the Electric Power Engineering Centre (EPECentre), University of Canterbury, on behalf of Orion to determine what are the primary causes of the high harmonic levels and provide mitigation options. Several farms with installed irrigation pumps were visited and the harmonic current and voltage levels were measured when the pumps were operating. Substation measurements were also simultaneously taken. A computer harmonic model of the local 11 kV network and loads was created that provided an accurate description of actual network conditions. An examination of Orion's system from the view of harmonic management was performed. The investigation revealed that the most significant cause of high harmonics levels is the comparatively large harmonic current injections by local irrigation pumps using Variable Speed Drives. A secondary cause is resonances in the network, often dynamically created by Power Factor (PF) capacitors switching online at various farms. To keep the rural network infrastructure in an effective and sustainable operating condition, mitigation measures are needed. Options researched included simulations of harmonic filters placed at various network points, and the use of alternate vector group transformers. Suggestions are made regarding objectives for harmonic limits at different network voltage levels, so as to determine harmonic limits for load installations.

An Investigation of Excessive Rural Network Harmonic Levels Caused by Particular Irrigation Pumps

In recent years, many countries have started to integrate the power system with more advanced information and communication technologies With transforming the electrical data to useful information, the stability and reliability of power system operation can be secured By observing this world-wide trend, it is believed that the development of smart grid would be the vital strategy for energy saving, integration of renewable energy resources, and improvement of power quality Meanwhile, the related measuring and control equipments are necessary to redesign based on information and communication technologies (ICT), which are key factors to the success of the smart grid implementation This paper gives an overview of some important issues and techniques for the enhancement of power quality monitoring and analysis when deploying the smart grid

Neville R. Watson

Papers

Subject Definition and Objectives

Incorporation of VSC transmission in power-flow simulation

STATCOM Performance of A Multi-Level Voltage Reinjection Converter

An Investigation of Excessive Rural Network Harmonic Levels Caused by Particular Irrigation Pumps

Monitoring issues and analysis techniques-smart grid aspect of power quality