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

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

The author evaluates the state of the art in pulsewidth modulation for AC drives fed from three-phase voltage source inverters. Feedforward and feedback pulsewidth modulation schemes with relevance for industrial application are described and their respective merits and shortcomings are explained. Secondary effects such as the influence of load-current dependent switching time delay and transients in synchronized pulsewidth modulation schemes are discussed, and adequate compensation methods are presented. Recorded oscillograms illustrate the performance of the respective pulsewidth modulation principles. The author provides a guideline and quick reference for the practicing engineer to decide which methods should be considered for an application of a given power level, switching frequency, and dynamic response. >

Pulsewidth modulation-a survey

This paper presents a review of recently used direct torque and flux control (DTC) techniques for voltage inverter-fed induction and permanent-magnet synchronous motors. A variety of techniques, different in concept, are described as follows: switching-table-based hysteresis DTC, direct self control, constant-switching-frequency DTC with space-vector modulation (DTC-SVM). Also, trends in the DTC-SVM techniques based on neuro-fuzzy logic controllers are presented. Some oscillograms that illustrate properties of the presented techniques are shown.

Direct torque control of PWM inverter-fed AC motors - a survey

This paper gives an overview of medium-voltage (MV) multilevel converters with a focus on achieving minimum harmonic distortion and high efficiency at low switching frequency operation. Increasing the power rating by minimizing switching frequency while still maintaining reasonable power quality is an important requirement and a persistent challenge for the industry. Existing solutions are discussed and analyzed based on their topologies, limitations, and control techniques. As a preferred option for future research and application, an inverter configuration based on three-level building blocks to generate five-level voltage waveforms is suggested. This paper shows that such an inverter may be operated at a very low switching frequency to achieve minimum on-state and dynamic device losses for highly efficient MV drive applications while maintaining low harmonic distortion.

Medium-Voltage Multilevel Converters—State of the Art, Challenges, and Requirements in Industrial Applications

Wireless power transfer system (WPTS)-based wireless electric vehicles, classified into roadway-powered electric vehicles (RPEVs) and stationary charging electric vehicles (SCEVs), are in the spotlight as future mainstream transportations. RPEVs are free from serious battery problems such as large, heavy, and expensive battery packs and long charging time because they get power directly from the road while moving. The power transfer capacity, efficiency, lateral tolerance, electromagnetic field, air-gap, size, weight, and cost of the WPTSs have been improved by virtues of innovative semiconductor switches, better coil designs, roadway construction techniques, and higher operating frequency. Recent advances in WPTSs for RPEVs are summarized in this review paper. The fifth- and sixth-generation online electric vehicles, which reduce infrastructure cost for commercialization, and the interoperability between RPEVs and SCEVs are addressed in detail in this paper. Major milestones of the developments of other RPEVs are also summarized. The rest of this paper deals with a few important technical issues such as coil structures, power supply schemes, and segmentation switching techniques of a lumped inductive power transfer system for RPEVs.

Modern Advances in Wireless Power Transfer Systems for Roadway Powered Electric Vehicles

A pulsewidth modulation (PWM) technique is proposed, intended particularly for the reduction of the harmful effects of the harmonics in the inverter-fed drive systems. The approach is based on the minimization of the rms value of the current harmonics in the motor by a proper choice of the commutation angles. Switching patterns are calculated for a different number of commutations per period, for both single-phase and three-phase half-bridge inverters. In the case of the single-phase, an analytical procedure is developed which simplifies the computations. Comparisons are made of the results thus obtained with those given by other PWM techniques in use.

Optimal Pulsewidth Modulation for Feeding AC Motors

Wireless power transfer systems (WPTSs) with inductive coupling are advantageously used to charge the battery pack of electric vehicles. They basically consist of coil coupling, power supply circuitry connected to the transmitting side of the coil coupling, and power-conditioning circuitry connected to the receiving side of the coil coupling. This paper presents the design and implementation of a wireless power transfer (WPT) battery charger for an electric city car. A short overview on the working principles of a series–series resonant WPTS is given before describing in detail the design procedure of the power circuitry needed for its operation, i.e., an alternating-current–direct-current converter cascaded by a high-frequency inverter in the transmitting section and a diode rectifier cascaded by a chopper in the receiving section. The coil coupling with spiral coils is designed with the help of a finite-element-method code. A prototype of the WPT battery charger is built up according to the design results, and experiments that validate the design procedure are carried out.

Design and Experimentation of WPT Charger for Electric City Car

The applications of a variable-structure system (VSS) to the control of a switched reluctance motor (SRM) drive is presented. After reviewing the operation of an SRM drive, a VSS-based scheme is formulated to control the drive speed. The scheme is then designed and tested by simulation. The results show that the VSS control is effective in reducing the torque ripple of the motor, compensating for the nonlinear torque characteristics, and making the drive insensitive to parameter variations and disturbances. >

Giuseppe Buja

Papers

Direct torque control of PWM inverter-fed AC motors - a survey

Modern Advances in Wireless Power Transfer Systems for Roadway Powered Electric Vehicles

Optimal Pulsewidth Modulation for Feeding AC Motors

Design and Experimentation of WPT Charger for Electric City Car

Variable structure control of an SRM drive