Marcelo A. Perez

Recent Advances and Industrial Applications of Multilevel Converters

Multilevel converters have been under research and development for more than three decades and have found successful industrial application. However, this is still a technology under development, and many new contributions and new commercial topologies have been reported in the last few years. The aim of this paper is to group and review these recent contributions, in order to establish the current state of the art and trends of the technology, to provide readers with a comprehensive and insightful review of where multilevel converter technology stands and is heading. This paper first presents a brief overview of well-established multilevel converters strongly oriented to their current state in industrial applications to then center the discussion on the new converters that have made their way into the industry. In addition, new promising topologies are discussed. Recent advances made in modulation and control of multilevel converters are also addressed. A great part of this paper is devoted to show nontraditional applications powered by multilevel converters and how multilevel converters are becoming an enabling technology in many industrial sectors. Finally, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

A Survey on Cascaded Multilevel Inverters

Cascaded multilevel inverters synthesize a medium-voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltages and input currents and also outstanding availability due to their intrinsic component redundancy. Due to these features, the cascaded multilevel inverter has been recognized as an important alternative in the medium-voltage inverter market. This paper presents a survey of different topologies, control strategies and modulation techniques used by these inverters. Regenerative and advanced topologies are also discussed. Applications where the mentioned features play a key role are shown. Finally, future developments are addressed.

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 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.

Circuit Topologies, Modeling, Control Schemes, and Applications of Modular Multilevel Converters

Modular multilevel converters have several attractive features such as a modular structure, the capability of transformer-less operation, easy scalability in terms of voltage and current, low expense for redundancy and fault tolerant operation, high availability, utilization of standard components, and excellent quality of the output waveforms. These features have increased the interest of industry and research in this topology, resulting in the development of new circuit configurations, converter models, control schemes, and modulation strategies. This paper presents a review of the latest achievements of modular multilevel converters regarding the mentioned research topics, new applications, and future trends.

Predictive Control of AC–AC Modular Multilevel Converters

Multilevel converters can reach medium-voltage operation increasing the efficiency of high-power applications. Among the existing multilevel converter topologies, the modular multilevel converter (MMC) provides the advantages of high modularity, availability, and high power quality. Moreover, the main advantage compared to cascaded multilevel converters is the lack of an input transformer which results in a reduction of cooling requirements, size, and cost. One of the drawbacks of this topology when used as an ac-ac converter is the input and output frequency components in the control loop, resulting in a more complex controller design. In this paper, a single-phase ac-ac MMC predictive control approach is proposed. The controller minimizes the input, output, and circulating current errors and balances the dc voltages. Experimental results show the performance of the proposed predictive control scheme.

Predictive Control Algorithm Technique for Multilevel Asymmetric Cascaded H-Bridge Inverters

Predictive control algorithms have been proposed for power electronic converters, featuring a high performance in terms of dynamic behavior. This is true due mainly to the accurate modeling and the finite set of inputs or possible switching combinations. However, when it is used in multilevel converters, the dynamic performance is degraded, because the optimization algorithm needs to evaluate and search over a large number of possible switching combinations. In this paper, a predictive control algorithm, which exhibits high dynamic performance for multilevel converters, is proposed. The algorithm reduces the complexity of calculations and the number of possible combinations, allowing the use of predictive control with a large number of switching states. Experimental results on a 27-level asymmetric multicell converter, which validate the proposed algorithm, are presented.

Model Predictive Control of an AFE Rectifier With Dynamic References

In this paper, a finite control set model predictive controller for closed-loop control of an active front-end rectifier is presented. The proposed method operates in discrete time and does not require additional modulators. The key novelty of the control algorithm presented lies in the way dynamic references are handled. The control strategy is capable of providing suitable references for the source active power and the rectified voltage, without requiring additional control loops. Experimental results show that fast and accurate tracking of dynamic dc voltage and reactive power references can be achieved, while respecting the restrictions on maximum power levels of the rectifier.

Powering the Future of Industry: High-Power Adjustable Speed Drive Topologies

The HP-ASD technology has experienced a huge development in the last decade. This can be appreciated by the large number of recently introduced drive configurations on the market. In addition, many industrial applications are reaching MV operation and megawatt range or have experienced changes in requirements on efficiency, performance, and power quality, making the use of HP-ASDs more attractive. It can be concluded that, HP-ASDs is an enabling technology ready to continue powering the future of industry for the decades to come.

High-Performance Motor Drives

This article reviews the present state and trends in the development of key parts of controlled induction motor drive systems: converter topologies, modulation methods, as well as control and estimation techniques. Two- and multilevel voltage-source converters, current-source converters, and direct converters are described. The main part of all the produced electric energy is used to feed electric motors, and the conversion of electrical power into mechanical power involves motors ranges from less than 1 W up to several dozen megawatts.

A Robust Phase-Locked Loop Algorithm to Synchronize Static-Power Converters With Polluted AC Systems

In this paper, a phase-locked loop algorithm appropriated for digital-signal-processor-based control implementations, where the operation of a static-power converter needs to be synchronized with an ac network, is presented. The proposed algorithm includes a multiplier, a filter, a feedback closed loop, and a numerically controlled oscillator stage. As a result, a discrete sine (and cosine) signal is generated in synchronism with the fundamental component of an external-reference (ER) signal. Moreover, the sampling period of the algorithm is adjusted at each sampling instant such that an integer number of sampling periods per period of the ER signal is ensured. This is the main feature, and it is achieved by using a discrete rectangular window filter and a discrete controller. The proposed algorithm code is simple, stable, and presents high noise rejection. A comprehensive theoretical justification and various rigorous experimental tests are included.