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

Multi-level Current Reinjection (MLCR) concept adds self commutation capability to thyristors, and produces a high quality line current waveforms and provides reactive power compensation in current source converters (CSC) Multi-level conversion is applied to generate the required optimum linear multilevel injection current which, when reinjected to the ac side, reduces the line current total harmonic distortion (THD) and forces the thyristor current to be zero In this paper a comparative study is carried out for a 3-level, 5-level, and 7-level thyristor based MLCR CSC in terms of line current THD obtained, reinjection transformer requirements, reinjection switch ratings, and reinjection control circuitry complexities Extensive PSCAD/EMTDC simulations are presented for comparing the different m-level reinjection schemes

https://ieeexplore.ieee.org/iel5/6389590/6401249/06401300.pdf

m-level thyristor based MLCR CSC: A comparative study

By setting up an identical test system, the authors have shown that the two main algorithms used for the simulation of AC/DC disturbances, namely TCS (transient converter simulation) and EMTDC, can be made to agree in their prediction of the dynamic responses. The TCS algorithm, though reputed to be less efficient, uses fewer approximations and provides automatic selection of optimal integration steps. As a result the TCS responses are very consistent. With careful selection of the integration step the EMTDC program can produce practically the same responses as the state variable technique for reasonably symmetrical conditions. However some deterioration occurs with highly asymmetrical disturbances. This has been traced to the phase advance prediction, required by the subsystem concept, thus the EMTDC algorithm provides a very efficient solution at the expense of some accuracy. It can be concluded that both the EMTDC and TCS algorithms can be used with confidence to simulate the transient response of AC/DC convertors.

http://ieeexplore.ieee.org/iel3/1210/4018/00153932.pdf

A comparison of HVDC transient simulation algorithms

Self‐Commutating Conversion

With the exceptions of a few auxiliary components, the electrical power system is a continuous system, which can be represented mathematically by a system of differential and algebraic equations. A convenient form of these equations is the state variable formulation, in which a system of n first-order linear differential equations results from an n order system. The state variable formulation is not unique and depends on the choice of state variables. The following state variable realisations have been described in this chapter: successive differentiation, controller canonical, observer canonical and diagonal canonical. Digital simulation is by nature a discrete time process and can only provide solutions for the differential and algebraic equations at discrete points in time, hence this requires the formulation of discrete systems. The discrete representation can always be expressed as a difference equation, where the output at a new time point is calculated from the output at previous time points and the inputs at the present and previous time points.

Neville R. Watson

Papers

m-level thyristor based MLCR CSC: A comparative study

A comparison of HVDC transient simulation algorithms

Self‐Commutating Conversion

Analysis of continuous and discrete systems

Multilevel Voltage Source Conversion