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

Electric spring (ES) as a new effective way to solve the power quality issues caused by the uncertainty of wind and photovoltaic (PV) power, has the advantages of small volume, flexible configuration and low cost. Aiming at improving the dynamic responses of the existing power control for ES-2, a new control with in-depth analysis on the decoupling of the active and reactive powers is proposed in this paper. By introducing second order generalized integrator phase locked loop (SOGI-PLL) and fictitious-axis emulator (FAE) into the control algorithm, the virtual orthogonal voltage and current signals were constructed and the mathematic model of ES-2 in the dq axis synchronous rotating reference frame was established. Then, the control system consisting of three closed loops, namely active power loop, current loop and ES voltage loop, is arranged. Among the three loops, a damped proportional resonance (PR) controller is adopted in the ES voltage loop to ensure the accurate control of the output voltage of ES-2. Instead, traditional PI controllers are used for the current and power loops. Finally, the effectiveness of the proposed decoupled power control is validated by both simulation and experimental results.

/pdf/decoupled-power-control-with-indepth-analysis-of-single-3wc5x7er8w.pdf

Decoupled Power Control With Indepth Analysis of Single-Phase Electric Springs

Electric Spring (ES) is an emerging technology intended to stabilize the voltage across the critical load (CL) of an end-user in the presence of fluctuations of the grid power. The most advanced way of controlling the so-called second generation of ES relies on the handling of both active and reactive power. However, the strategies used to implement such a control suffer from either the need of an a-priori knowledge of circuit parameters or a slow response to the grid power fluctuations. In this paper, a control strategy is proposed that overcomes these inconveniences. It relies on two problem-solving solutions, namely the closed-loop control of the dq components of the current drawn by the end-user and a feedback of the ES output current into the ES command. The setup of the proposed power decoupling control has just the features of being no affected by the circuit parameters and exhibiting an enhanced dynamic behavior. The features are validated by both simulation and experimental results.

/pdf/a-parameter-exempted-high-performance-power-decoupling-1y8s7zjvi5.pdf

A Parameter-Exempted, High-Performance Power Decoupling Control of Single-Phase Electric Springs

From 1 to 3 October 2008 the Formula Electric and Hybrid Italy took place in the Safety Testing Center of Fiat Group Automobiles in Orbassano (TO), Italy. This fourth edition of Formula EHI, an international competitive demonstration of research outcomes from university student teams, has brought to the attention of the public and of the industry new technologies and innovative applications in the area of the systems addressing the ecological mobility. Teams from five European countries were the protagonists of the event. Several projects, components, systems and concept have been presented, related to advanced technologies for battery electric, hybrid and fuel cell vehicles. New technology hybrid, fuel cell and electric vehicles took part to the dynamic test on track for the evaluation of energy efficiency performance and dynamic behaviour. The 2008 event was a further step of the editions of Formula TECH held in the previous years and offered a benchmarking overview of the progress of the technology in the field of electrically propelled vehicles.

/pdf/new-technologies-demonstrated-at-formula-electric-and-hybrid-18mc1o3pfu.pdf

New technologies demonstrated at Formula Electric and Hybrid Italy 2008

The application of a variable structure system (VSS) to the control of a switched reluctance motor (SRM) drive is presented. The operation of an SRM drive is reviewed, and a VSS-based scheme is formulated to control the drive speed. The scheme is then 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. >

http://ieeexplore.ieee.org/iel2/637/6472/00254509.pdf

Giuseppe Buja

Papers

Decoupled Power Control With Indepth Analysis of Single-Phase Electric Springs

A Parameter-Exempted, High-Performance Power Decoupling Control of Single-Phase Electric Springs

New technologies demonstrated at Formula Electric and Hybrid Italy 2008

Variable structure control of a SRM drive

Design and analysis of genetic algorithm and BP neural network based PID control for boost converter applied in renewable power generations