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 harmonic levels in a distribution system are becoming more important as many new power electronic based devices are being deployed. In order to manage the harmonic levels, it is important to know them. Direct measurement of harmonics at all locations is too costly, yet obtaining a system-wide view is important. Harmonic State Estimation (HSE) is a cost-effective alternative to direct monitoring of all the harmonics. To date, it has been applied mostly to transmission systems but in this paper, it is applied to a model of an actual distribution system. An actual distribution feeder, which is typical of many other feeders in the system is modelled in Open Distribution System Simulator (OpenDSS) and harmonic penetration study performed. Voltage and current harmonics at selected locations are then used as the measurements. Using these measurements and electrical network data, HSE is performed based on a robust mathematical technique, Singular Value Decomposition (SVD). The estimated results are compared with those obtained from harmonic penetration simulations performed in OpenDSS to assess the accuracy of the estimation. Locations and number of measurements that can give maximum observability with reasonable accuracy are also identified.

Application of harmonic state estimation to a distribution system

This paper has proposed a power quality monitoring system on the detection of power disturbance in real-time by using an embedded system. It can be controlled and monitored by its function via Ethernet network. This system has been developed to monitor and detect any disturbance signals in power lines. If any phase in the power lines has disturbance, the monitoring system will store the fault data into the chosen memory card. This developed system can allow users to control and receive data from the remote hardware via Ethernet network by using UDP and TCP/IP protocol. To transfer the disturbance file that has been stored in the memory card to PC, the embedded TFTP server is applied in this step. There are some advantages of using the developed application software: it can control the power quality monitoring hardware which being installed at the remote sites; can display the detected fault data in the waveform; and also can connect to the various number of the monitoring hardware.

	 

	Key words:  Power quality, UDP, TCP/IP, TFTP, ethernet network.

https://www.academicjournals.org/article/article1380793462_Yingkayun et al.pdf

Power quality monitoring system based on embedded system with network monitoring

This paper reports the issues and challenges behind the proposal to include interharmonic limits in the next revision of the IEEE Standard 519 as discussed within the interharmonic distortion sub-group formed in the framework of the Harmonics WG (519) of the IEEE PES Transmission & Distribution Committee.

Issues and Challenges Related to Interharmonic Distortion Limits

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.

DC Ripple Reinjection: A Review

The frequency of the power system experiences variations due to various factors including intermittent renewable and distributed generators, and imbalance between generated and consumed power. This frequency variation may affect the operation of grid connected converters. For example, in case of repetitive control of grid connected converters, the grid electrical signal acts a reference signal and repetitive control requires exact knowledge of the reference signal. This paper contributes to the performance analysis of conventional repetitive controllers when the frequency of the reference signal is not fixed but is rather subjected to variations. It also proposes a novel method for making the repetitive controllers frequency adaptive i.e. the performance of the controller is not affected in variable frequency reference signal environments. The proposed scheme includes a Taylor Series expansion based fractional delay filter along with a typical repetitive controller. The proposed frequency-adaptive scheme enables the repetitive controller to maintain its good performance in both, fixed and variable frequency, environments. The novel frequency-adaptive controller offers fast on-line tuning and update of the controller when the frequency of the reference signal varies.

Neville R. Watson

Papers

Application of harmonic state estimation to a distribution system

Power quality monitoring system based on embedded system with network monitoring

Issues and Challenges Related to Interharmonic Distortion Limits

DC Ripple Reinjection: A Review

An adaptive repetitive controller for three-phase PWM regenerative rectifiers