Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

Multilevel inverters: a survey of topologies, controls, and applications

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.

/pdf/recent-advances-and-industrial-applications-of-multilevel-26fluutoc9.pdf

Recent Advances and Industrial Applications of Multilevel Converters

This paper reviews the current status and implementation of battery chargers, charging power levels, and infrastructure for plug-in electric vehicles and hybrids. Charger systems are categorized into off-board and on-board types with unidirectional or bidirectional power flow. Unidirectional charging limits hardware requirements and simplifies interconnection issues. Bidirectional charging supports battery energy injection back to the grid. Typical on-board chargers restrict power because of weight, space, and cost constraints. They can be integrated with the electric drive to avoid these problems. The availability of charging infrastructure reduces on-board energy storage requirements and costs. On-board charger systems can be conductive or inductive. An off-board charger can be designed for high charging rates and is less constrained by size and weight. Level 1 (convenience), Level 2 (primary), and Level 3 (fast) power levels are discussed. Future aspects such as roadbed charging are presented. Various power level chargers and infrastructure configurations are presented, compared, and evaluated based on amount of power, charging time and location, cost, equipment, and other factors.

/pdf/review-of-battery-charger-topologies-charging-power-levels-85yy2igx2w.pdf

Review of Battery Charger Topologies, Charging Power Levels, and Infrastructure for Plug-In Electric and Hybrid Vehicles

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

At present time, the most common electrical vehicle (EV) chargers employ a two-stage design, i.e., a front-end AC/DC stage + an isolated DC/DC converter. In this paper, an isolated dual-active-bridge (DAB) based single-stage AC/DC converter was proposed, which has the power-factor-correction (PFC) and zero-voltage-switching (ZVS) functions over the full-load range. By reducing one power stage and eliminating the large DC link capacitor, a high efficiency and high power density are achieved. Such topology can be used as a modular building block to scale up to 50kW by serial connecting the input terminals and paralleling output terminals. A novel energy-balanced variable switching frequency control for such input-series-output-parallel (ISPO) modular designed is proposed. A single-phase d-q transformation is implemented to achieve zero steady-state error. Simulation analysis and experimental validation are presented.

A novel energy balanced variable frequency control for input-series-output-parallel modular EV fast charging stations

As an industrial customer of the utility, electrical arc furnace (EAF) is the major flicker source that degrades the grid power quality. As a possible solution, STATCOMs with high bandwidth can be used. In this paper, the normalized model of a CMC-based STATCOM and an EAF model are introduced, and then a DQ-model based control strategy is proposed for flicker mitigation. Case studies are conducted for STATCOM applying to a 40 MVA EAF arc furnace. Simulation results verify the controllers' stability and performance. A transient network analyzer (TNA) is developed to experimentally test the developed controller.

Modelling and control of a cascade-multilevel converter-based STATCOM for electric arc furnace flicker mitigation

This work presents the design and experimental demonstration of a superior high power device, self-powered emitter turn-off thyristor (SPETO). Different from the conventional high power devices which require the external power input for their gate drivers, SPETO achieves optically controlled turn-on and turn-off, and all the internal power required is self-generated. Low loss gate drive circuit is implemented which allows the simple power-up operation. During normal switching operation, SPETO obtains power for the gate drive during its turn-on operation. SPETO also maintains the reported advantages of ETO such as the high switching frequency capability (over 2 kHz), large snubberless turn-off capability (5000 A/2800 V), low conduction and switching losses, and easy for series and parallel operation. SPETO greatly reduces the cost and increase the reliability of the power converters since no external power supply for device gate drive is required. SPETO is therefore suitable for the high power high frequency voltage source converter applications. Novel switching strategy is also introduced to minimize the gate drive power requirement.

SPETO: a superior power switch for high power, high frequency, low cost converters

Battery is one of the most important energy storage devices in high power energy storage applications. It is widely used in the plug-in hybrid electric vehicles (PHEVs) and energy storage systems for renewable power generation such as wind and PV. In conventional series-connected high capacity battery string, due to the imbalance of battery cells, there are a few issues such as the cell damage due to over charge or over discharge, reliability and safety concerns. Conventional approaches to address these issues include the battery monitor system (BMS) and cell equalizer circuits. With BMS battery pack performance is still limited by the weakest cell in the string. The cell equalizer is limited by the current rating of the circuit, the equalization speed and the additional cost and weight. In this paper, a new concept of distributed energy storage device (DESD) module is proposed. Instead of using one high power DC-DC converter which connects to the whole battery string, a few distributed high voltage gain, high frequency and high efficiency bi-directional DC-DC converters are integrated with small battery packs respectively to form DESD modules. The module outputs are connected in parallel to form a battery energy storage system. The advantages and challenges of the DESD module are presented in this paper. A 200kHz, 400V to 12.8V, 256W soft switched bi-directional DC-DC converter is demonstrated for DESD modularization.

High-frequency high-efficiency DC-DC converter for distributed energy storage modularization

A series of simulations were carried out to investigate the failure mechanism of large area silicon power diodes Static breakdown behavior of high voltage diodes is first investigated at elevated temperatures Sustain-mode dynamic avalanche is then discussed It was found that under isothermal and homogeneity condition, the reverse bias safe operation area (RBSOA) of power diodes is the same as the sustain-mode dynamic avalanche After introducing current inhomogeneity, the failure will occur at reverse power density that is much less than the RBSOA predicted by the sustain-mode dynamic avalanche The failure mechanism of power diodes is then proposed based on these findings

Alex Q. Huang

Papers

A novel energy balanced variable frequency control for input-series-output-parallel modular EV fast charging stations

Modelling and control of a cascade-multilevel converter-based STATCOM for electric arc furnace flicker mitigation

SPETO: a superior power switch for high power, high frequency, low cost converters

High-frequency high-efficiency DC-DC converter for distributed energy storage modularization

Analysis of the turn-off failure mechanism of silicon power diode