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

A three-phase converter configuration, with each phase consisting of a series chain of H-bridges has become a popular multilevel solution for STATCOM application. Such a configuration, however, is not suitable for HVDC transmission. A new concept, where the series chain of H-bridge cells is used to derive a multilevel voltage reinjection waveform, is described in a companion paper. Its application to HVDC transmission is discussed in this paper and extensive use is made of EMTDC simulation to verify its steady-state and dynamic behavior.

Cascaded H-Bridge Voltage Reinjection—Part II: Application to HVDC Transmission

The use of Fourier descriptors (FD) for the assessment of frequency coupling matrices (FCM) of power electronic devices is considered. After some recalls on FDs, FCM approach is discussed showing how the matrices elements can be built basing on the use of maximum two FDs under linearity hypothesis. Then, a non-linearity index that allows to check the validity of the assumed “linearity hypothesis” and to quantify the obtainable accuracy is introduced. Numerical simulations on two very simple non linear circuits are performed to show the sensitivity of the FCM elements to magnitude and phase angle variation of the background harmonic distortion using FDs and the usefulness and the behavior of the non linearity index.

/pdf/on-the-use-of-fourier-descriptors-for-the-assessment-of-1kmtn5tdoz.pdf

On the use of fourier descriptors for the assessment of frequency coupling matrices of power electronic devices

This paper addresses the problem of harmonic state estimation (HSE) of a power system whose network parameters are known to be within certain tolerance bounds. The harmonic voltage and current phasors at harmonics of interest are measured by using adequate numbers of phasor measurement units. The HSE is formulated based on the weighted least squares (WLS) criterion as a parametric interval linear system of equations. The solutions are obtained as interval numbers representing the outer bound of state variables. A method for adjusting the weight used in WLS which takes uncertain network parameters into consideration is also proposed. The proposed HSE algorithm is applied to the three-phase power systems and the results from numerical experiments show that the bounds of state variables obtained by the proposed method agree with those estimated by performing Monte Carlo simulations but with much shorter computation time.

On harmonic state estimation of power system with uncertain network parameters

This paper presents a novel maximum power point tracking (MPPT) algorithm for load protection based on output sensing control. All MPPTs are based on input sensing and there is a drawback in applications which load protection is essential. This drawback can be addressed by applying two more sensors at the output. However having two sensors at input side as well as two more at output will increase the size and cost of the controller.

A novel MPPT algorithm for load protection based on output sensing control

State estimation techniques are used as it is infeasible to monitor completely the whole electrical network. However with strategically placed measurements, estimation techniques can determine the parameters at unmonitored locations. Fundamental frequency state estimation is now a standard tool in modern power systems. Estimation techniques have been extended to Harmonic State Estimation (HSE) and this paper further extends the estimation techniques to Transient State Estimation (TSE). This technique is capable of estimating the complete system state using partial measurements and hence giving information on the fault location. It partitions the system nodes according to the type of branches that are connected to them. The algorithm is presented, which uses an efficient formulation of the network equations via a diakoptical segregation methodology, and demonstrated on the Lower South Island of the New Zealand test system.

Neville R. Watson

Papers

Cascaded H-Bridge Voltage Reinjection—Part II: Application to HVDC Transmission

On the use of fourier descriptors for the assessment of frequency coupling matrices of power electronic devices

On harmonic state estimation of power system with uncertain network parameters

A novel MPPT algorithm for load protection based on output sensing control

Transient State Estimation