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 paper presents a technology review of voltage-source-converter topologies for industrial medium-voltage drives. In this highly active area, different converter topologies and circuits have found their application in the market. This paper covers the high-power voltage-source inverter and the most used multilevel-inverter topologies, including the neutral-point-clamped, cascaded H-bridge, and flying-capacitor converters. This paper presents the operating principle of each topology and a review of the most relevant modulation methods, focused mainly on those used by industry. In addition, the latest advances and future trends of the technology are discussed. It is concluded that the topology and modulation-method selection are closely related to each particular application, leaving a space on the market for all the different solutions, depending on their unique features and limitations like power or voltage level, dynamic performance, reliability, costs, and other technical specifications.

Multilevel Voltage-Source-Converter Topologies for Industrial Medium-Voltage Drives

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

Power electronics

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.

A Survey on Cascaded Multilevel Inverters

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

In practice, a dead-time is always provided between the complementary switching instances of the inverter phase-leg devices At higher operating frequencies, the dead-time issues in wireless power transfer (WPT) systems become critical, especially as the power level increases In certain operating conditions, the dead-time effect in wireless power transfer system affects the switching characteristics Consequently, the switching losses in the power semiconductor devices increase and also impact the efficiency of the overall system In this paper, a simple control scheme is proposed to eliminate the dead-time effect (or voltage polarity reversal) in the WPT inverter The proposed control scheme monitors the inverter output voltage, and the switching frequency is auto-tuned to eliminate the undesired switching instances in the inverter voltage The proposed control scheme is validated using the closed-loop simulations in PLECS, and the experimental results on a 56 kW WPT prototype are also presented After eliminating the voltage-polarity-reversal at the inverter output, the inverter losses were reduced by ∼40%, and the overall system losses were reduced by ∼17%

A Control Scheme to Mitigate the Dead-Time Effects in a Wireless Power Transfer System

The output power of a wireless power transfer (WPT) system varies with load and coupling factor of the inductively coupled coils. This paper presents a method to control the output power of primary side LCC and secondary side series tuned WPT system using information of primary side variables. In this approach, a secondary side control system or secondary side sensors are not needed. Detailed mathematical derivations are given to identify and justify the suitable primary side variable that accomplishes the desired purpose without the need of any secondary side communications. Simulation results presented validate the proposed scheme.

Control of Output Power in Primary Side LCC and Secondary Series Tuned Wireless Power Transfer System without Secondary Side Sensors

In this article, the effect of the dead-time on a single-phase wireless power transfer (WPT) system is studied in detail. In practice, the dead-time is always placed between the complementary switching pulses of the inverter phase-leg. At higher operating frequencies, the dead-time issues in the resonant inverter become critical, especially as the power level increases. The detailed analysis of the dead-time on a WPT system is discussed for different operating conditions of the inverter duty-cycle and power factor. The switching characteristics of the WPT system inverter are analyzed, and the notch phenomenon that appears at the output of the inverter is also discussed. A notch equation based on the observations is derived to predict the notch occurrence during the system operation. Furthermore, the mathematical expressions are presented for different notch conditions. Subsequently, the effect of the notches on the sensitivity and the power transfer of the series–series compensated WPT system is analyzed. Finally, the approach is verified experimentally on an 8-kW WPT system prototype, and the results are compared with the theoretical analysis.

The Impact of Inverter Dead-Time in Single-Phase Wireless Power Transfer Systems

Overview of the Oak Ridge National Laboratory Advanced Manufacturing Integrated Energy Demonstration Project: Case Study of Additive Manufacturing as a Tool to Enable Rapid Innovation in Integrated Energy Systems


 In this technical paper, design, analysis and comparison of insulated metal substrates for high power wide-bandgap semiconductor-based power modules is discussed. The paper starts with technical description and discussion of state-of-the-art direct bonded copper substrates with different ceramic insulators such as AlN, Al2O3 and Si3N4. This is followed by introduction of insulated metal substrates, material properties and options on each layer, and design approach for high power applications. The properties of dielectric thickness, and impact on power handling capability of the substrate are discussed. Insulated metal substrate design approach for SiC MOSFET based power modules is presented. Finite element analysis-based characterization and comparison of different designs including steady-state and transient thermal response is presented. The results show that IMS is a promising alternative to DBC in high power modules with improved transient thermal performance. IMS provides flexible building structure with multi-layer stacking options and variable thicknesses at different layers.

Burak Ozpineci

Papers

A Control Scheme to Mitigate the Dead-Time Effects in a Wireless Power Transfer System

Control of Output Power in Primary Side LCC and Secondary Series Tuned Wireless Power Transfer System without Secondary Side Sensors

The Impact of Inverter Dead-Time in Single-Phase Wireless Power Transfer Systems

Overview of the Oak Ridge National Laboratory Advanced Manufacturing Integrated Energy Demonstration Project: Case Study of Additive Manufacturing as a Tool to Enable Rapid Innovation in Integrated Energy Systems

Design, Analysis and Comparison of Insulated Metal Substrates for High Power Wide-Bandgap Power Modules