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

Time-triggered protocols are recognized to have a high degree of dependability. The purpose of this paper is to analyze by experiments their application to the networking of the devices installed aboard train. The paper starts by reviewing the current standard for the train communications. Then the operating principles of the time-triggered protocols are illustrated, a possible arrangement for a time-triggered network to be applied to a train is presented, and the TTP/C protocol is introduced. Afterwards the technical data of a commercial TTP/C board are illustrated and a prototypal network is set up with these boards to control an emulated train function. At last, experimental results showing the communication characteristics of the prototypal network are reported.

Experimental Analysis of a Time-Triggered Network Designed for Train Communications

The paper is concerned with the development of the propulsion system for two Light Electric Vehicles (LEVs), namely a city scooter and an electric bicycle. The propulsion system of the city scooter consists of a wheel motor for the traction and a lithium-ion battery for the energy storage. The propulsion system of the electric bicycle utilizes a fuel cell assisted by a supercapacitor bank for the energy supply.

Propulsion systems for Light Electric Vehicles

This paper (Part II), together with a companion one (Part I), deals with the fault-tolerant operation of a 5-phase permanent magnet (PM) brushless DC (BLDC) drive. In particular, this paper takes advantage of the drive model formulated in Part I to determine automatically the motor current supply, namely scheduling and magnitude of the currents for the surviving phases, in the cases of a drive with two and three open phase faults. Maximum magnitude of the supply currents is also determined by equating the rms value of current in the most solicited phase to the nominal rms value Open faults of adjacent and non-adjacent phases are studied and for each fault location, besides determining the motor current supply, the torque developed by the motor is calculated. The results indicate that the reduction in the motor torque as well as the extent of the torque ripple is depending on the relative location of the faults.

An algebraic approach to determine the current supply in a faulty 5-phase PM BLDC drive. Part II - application to the cases of two and three open phase faults

The main objective of this paper is to demonstrate the advantages of resonant power converters (RPC) in renewable energy sources. Due to their advantages over other topologies RPCs are more often used in many applications then after an overview of applications of RPC in different areas the paper focuses on the analysis, design, simulation and experimentation of an L s C s L p C p resonant circuit for renewable energy sources. To improve the dynamic performance of the converter supplying the resonant circuit, a hybrid control scheme, which combines both PWM and frequency control, is developed. Simulation and experimental results are achieved at full and half load conditions for a 3kW prototype. The parallel inductor Lp is taken as part of the magnetizing inductance, which therefore reduces the magnetic component count.

Resonant power converters applications: L s C s L p C p circuit for renewable energy sources as case study

DD coils are one of the most used coupling arrangements for the tracks and the pickups in dynamic wireless power transfer system. They reach a higher coupling coefficient with respect to conventional coil pairs with the same dimensions and assure a more effective and efficient power transfer to the electric vehicles. On the other hand, DD coils suffer of the phenomenon known as null power point, by which the power transferred to the pickup, is zero even if it is still partially coupled to the transmitting track coil. The null power points are typically removed by installing the so-called Q coil in the pickup. The power transferred to the Q coils is added to that harvested by the DD coil by a separate power converter so that the overall architecture of the receiving side of the dynamic wireless power transfer system results rather intricate. This paper presents a different approach to the problem of the null power points, based on the switching between two different supplying modes of the track DD coils. In front of a more complex architecture of the power supply system of the track, this approach gets rid of the Q coil and of the relevant power converter. The proposed solution is at first studied analytically with an approximated model of the DD coils and then verified by means of a FEM analysis and simulation.

Giuseppe Buja

Papers

Experimental Analysis of a Time-Triggered Network Designed for Train Communications

Propulsion systems for Light Electric Vehicles

An algebraic approach to determine the current supply in a faulty 5-phase PM BLDC drive. Part II - application to the cases of two and three open phase faults

Resonant power converters applications: L s C s L p C p circuit for renewable energy sources as case study

Avoiding Null Power Point in DD coils