This work is devoted to review and analyze the most relevant characteristics of multilevel converters, to motivate possible solutions, and to show that we are in a decisive instant in which energy companies have to bet on these converters as a good solution compared with classic two-level converters. This article presents a brief overview of the actual applications of multilevel converters and provides an introduction of the modeling techniques and the most common modulation strategies. It also addresses the operational and technological issues.

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The age of multilevel converters arrives

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

Annual Energy Outlook

Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.

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Multilevel Converters: An Enabling Technology for High-Power Applications

Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorialonthistechnology,coveringtheoperatingprincipleand the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.

Multilevel Converters: An Enabling Technology for High-Power Applications Multilevel converters generate voltage and current waveforms of improved quality, that can be used to power drives for trains and other vehicles, and many other applications.

One of the most recent topics in variable-structure systems theory is represented by the second-order sliding-mode control (2-SMC) methodology. This approach guarantees the same robustness and dynamic performance of traditional first-order SMC algorithms, and, at the same time, attenuates the chattering phenomenon, which is the main drawback in the actual implementation of this technique. In the present paper, a recently-proposed 2-SMC algorithm is used to synthesize a robust dc-drive control system which does not require current feedback and demands only rough information about the actual motor parameters. Stability and performance are analyzed, and an experimental comparison with a proportional-integral-based control scheme is reported.

Second-order sliding-mode control of DC drives

An optimal energy storage system (ESS) management procedure devoted to full renewable energy sources (RESs) exploitation is presented in this paper. It consists of an appropriate scheduling procedure and a real-time control strategy, which both aim to increase the RES penetration level as much as possible. In particular, the one-day-ahead scheduling procedure synthesizes the combined RES-ESS energy production profile with the aim of minimizing the RES energy production curtailments by means of ESS energy buffering. The real-time control strategy is developed in order to track the scheduled profile as well as possible by mitigating forecasting errors, thus improving RES reliability. The worth and effectiveness of the proposed management procedure is verified through a wide simulation study, which is carried out by means of the Matlab software package.

Real-Time Control Strategy of Energy Storage Systems for Renewable Energy Sources Exploitation

This paper presents the synthesis and practical implementation of a robust digital differentiator that provides the first and second derivative of a sampled smooth signal. The robustness of the proposed digital device, based on second-order sliding-modes (2-SMs), is analyzed with respect to measurement errors. Experimental results on an induction motor (IM) drive show that fast and accurate estimates of speed and torque can be obtained in several operating conditions by double differentiation of the encoder position measurement.

Robust speed and torque estimation in electrical drives by second-order sliding modes

Islanding is known as a management procedure of the power system that is implemented at the distribution level to preserve sensible loads from outages and to guarantee the continuity in electricity supply, when a high amount of distributed generation occurs. In this paper we study islanding on the level of the transmission grid and shall show that it is a suitable measure to enhance energy security and grid resilience. We consider the German and Italian transmission grids. We remove links either randomly to mimic random failure events, or according to a topological characteristic, their so-called betweenness centrality, to mimic an intentional attack and test whether the resulting fragments are self-sustainable. We test this option via the tool of optimized DC power flow equations. When transmission lines are removed according to their betweenness centrality, the resulting islands have a higher chance of being dynamically self-sustainable than for a random removal. Less connections may even increase the grid’s stability. These facts should be taken into account in the design of future power grids.

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Islanding the power grid on the transmission level: less connections for more security

Renewable energy sources will play an increasingly central role in the power network of the future. The will to reduce the dependence on fossil sources as well as growing environmental awareness, both individually and governmentally, is forcing governments throughout the world to invest an enormous amount of capital in renewable energy sources. The European Union, through its Energy and Climate Policy, has fixed an ambitious target: to provide, 20% of electricity from renewable sources by 2020. The additional volatility introduced by renewable energy source to the grid can be compensated by energy storage systems as well as by demand control measurements and by the reinforcement of the power grid. These solutions can improve the system reliability of the electric grid and the efficiency of the energy supply and give more flexibility to the system. This study analyzes the possibilities to use electric vehicles connected to the grid as energy storage system within a Virtual Power Plant structure. Through the formulation of an optimization problem the optimal number of electric vehicles has been evaluated.

Alfonso Damiano

Papers

Second-order sliding-mode control of DC drives

Real-Time Control Strategy of Energy Storage Systems for Renewable Energy Sources Exploitation

Robust speed and torque estimation in electrical drives by second-order sliding modes

Islanding the power grid on the transmission level: less connections for more security

Vehicles to grid (V2G) concept applied to a Virtual Power Plant structure