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.

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Recent Advances and Industrial Applications of Multilevel Converters

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

This paper presents a detailed description of finite control set model predictive control (FCS-MPC) applied to power converters Several key aspects related to this methodology are, in depth, presented and compared with traditional power converter control techniques, such as linear controllers with pulsewidth-modulation-based methods The basic concepts, operating principles, control diagrams, and results are used to provide a comparison between the different control strategies The analysis is performed on a traditional three-phase voltage source inverter, used as a simple and comprehensive reference frame However, additional topologies and power systems are addressed to highlight differences, potentialities, and challenges of FCS-MPC Among the conclusions are the feasibility and great potential of FCS-MPC due to present-day signal-processing capabilities, particularly for power systems with a reduced number of switching states and more complex operating principles, such as matrix converters In addition, the possibility to address different or additional control objectives easily in a single cost function enables a simple, flexible, and improved performance controller for power-conversion systems

Model Predictive Control—A Simple and Powerful Method to Control Power Converters

This paper addresses to some of the latest contributions on the application of Finite Control Set Model Predictive Control (FCS-MPC) in Power Electronics. In FCS-MPC , the switching states are directly applied to the power converter, without the need of an additional modulation stage. The paper shows how the use of FCS-MPC provides a simple and efficient computational realization for different control objectives in Power Electronics. Some applications of this technology in drives, active filters, power conditioning, distributed generation and renewable energy are covered. Finally, attention is paid to the discussion of new trends in this technology and to the identification of open questions and future research topics.

State of the Art of Finite Control Set Model Predictive Control in Power Electronics

Model predictive control (MPC) is a very attractive solution for controlling power electronic converters. The aim of this paper is to present and discuss the latest developments in MPC for power converters and drives, describing the current state of this control strategy and analyzing the new trends and challenges it presents when applied to power electronic systems. The paper revisits the operating principle of MPC and identifies three key elements in the MPC strategies, namely the prediction model, the cost function, and the optimization algorithm. This paper summarizes the most recent research concerning these elements, providing details about the different solutions proposed by the academic and industrial communities.

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Model Predictive Control for Power Converters and Drives: Advances and Trends

This paper presents a single-phase cascaded H-bridge converter for a grid-connected photovoltaic (PV) application The multilevel topology consists of several H-bridge cells connected in series, each one connected to a string of PV modules The adopted control scheme permits the independent control of each dc-link voltage, enabling, in this way, the tracking of the maximum power point for each string of PV panels Additionally, low-ripple sinusoidal-current waveforms are generated with almost unity power factor The topology offers other advantages such as the operation at lower switching frequency or lower current ripple compared to standard two-level topologies Simulation and experimental results are presented for different operating conditions

Control of a Single-Phase Cascaded H-Bridge Multilevel Inverter for Grid-Connected Photovoltaic Systems

This paper presents the implementation of a predictive control scheme for an indirect matrix converter. The control scheme selects the switching state that minimizes the reactive power and the error in the output currents according to their reference values. This is accomplished by using a prediction horizon of one sample time and a very intuitive control law. Experimental results with a 6.8-kVA indirect matrix converter prototype are provided in order to validate the proposed control scheme. The converter uses standard digital signal processor operating at a sampling frequency of 20 mus. It is shown that the idea of controlling this converter topology with a predictive approach can be implemented simply and input currents with unity power factor and a total harmonic distortion lower than 5% can be obtained.

Predictive control of an indirect matrix converter

This paper proposes a new modulation strategy for multilevel inverters, which selects voltage vectors that generate zero common-mode voltage in the load, working at low switching frequency. Experimental results confirm that the method is highly effective and simple to implement in a modern microprocessor. The voltage distortion (total harmonic distortion), the number of commutations, and the linearity are also studied. Finally, it is concluded that the proposed strategy is highly suited for inverters with a high number of levels.

A new modulation method to reduce common-mode voltages in multilevel inverters

Current-source rectifiers (CSRs) constitute a commonly used topology in high-power applications, featuring several advantages such as regeneration capability and high-quality currents. This paper presents a simple predictive control scheme for a CSR. The main achievements of the control scheme presented here are the simplicity in controlling the dc-link current and the generation of currents with unity displacement power factor. Experimental results are presented to validate the proposed control principle.

A Predictive Control Scheme for Current-Source Rectifiers

This paper analyzes the fault-tolerant operation of a Series Connected H-Bridge inverter topology (SCHB) supplying an induction machine. The standard approach considers a bypass of the faulty cells by means of a contactor and it carries out a reconfiguration of the modulator in order to generate balanced phase output voltages. The price that must be paid for this emergency operating mode is a reduction of the maximum voltage that the inverter can supply to the machine., therefore the limits for the torque and flux controllers must be also changed. In this work a standard stator flux oriented control strategy is modified to permit the operation the machine according to the new voltage limit. Experimental results are discussed, which validate the ideas presented in this work.

P. Correa

Papers

Control of a Single-Phase Cascaded H-Bridge Multilevel Inverter for Grid-Connected Photovoltaic Systems

Predictive control of an indirect matrix converter

A new modulation method to reduce common-mode voltages in multilevel inverters

A Predictive Control Scheme for Current-Source Rectifiers

Control Strategy Reconfiguration for a Multilevel Inverter Operating with Bypassed Cells